Acute weakness

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8.4 Acute weakness

Richard Lennon

Essentials

1 The fact that a child has acute weakness may be obscured by an inability to communicate and a smaller repertoire of activities. The possibility of a neuromuscular problem must be consciously considered by the clinician.
2 Conversely a small child may not move a limb because of pain rather than weakness. A history and examination for evidence of trauma should be performed and appropriate diagnostic imaging considered.
3 Respiratory insufficiency due to weakness, may occur with surprising rapidity and may be compounded by aspiration. Careful assessment and close monitoring for this complication must be made.
4 Abnormal reflexes are important in localising the cause of acute weakness. If some are absent especially distally it suggests a lower motor neurone dysfunction. If all are present it suggests muscle dysfunction and if they are increased it suggests an upper motor neurone weakness.
5 The presence of a sensory level indicates a spinal cord lesion. One should consider investigating this with an urgent MRI to determine whether or not urgent surgery is needed.

Introduction

The acutely weak child is challenging to the emergency physician because she/he can present in many different ways with many different diagnoses. In particular, the preverbal child may present with only regression in motor milestones or bruising on the face from increased frequency of falls. The diagnosis in such children can range from a tick bite to Duchenne pseudohypertrophic muscular dystrophy.

Presentation

In infants of less than three months, parents are usually quite sensitive to abnormalities of the infant’s behaviour. They may bring a baby in complaining of poor feeding, decreased activity or being ‘floppy’. The older infant may be noted to lose milestones such as ceasing to crawl or walk. ‘Ataxia’ may be the predominant feature in preschool and school-age children. Sometimes children may present with an associated feature of illness, such as the rash of dermatomyositis or an obvious engorged tick. In general, the older the child is, the more typical the presentation. However, even in this group, as in adults, there is a wide range of presentations, e.g. cranial nerve palsies in the Miller–Fisher variant of Guillain–Barré syndrome.

Trauma masquerading as weakness

Trauma is dealt with in detail in other chapters of the book. However, it should noted that non-accidental injury (NAI) can present as ‘acute weakness’ in the infant and young child. Shaken baby syndrome may present as a lethargic irritable child with little or no bruising. The apparent focal weakness may be due to an underlying fracture. Likewise, emotional and nutritional neglect may also lead to weakness. Hence, NAI must be considered in the differential diagnosis of the acutely weak child (see Chapter 18.2).

Primary survey approach

General inspection

This is done by looking for both cause and effect of the weakness. An abnormality of the primary survey severe enough to cause generalised weakness (e.g. respiratory distress) is usually the obvious presenting problem. Hypoglycaemia in a child can, in rare circumstances, present with focal weakness. It is important in the ‘weak’, floppy infant to consider the possibility of intussusception or other intra-abdominal pathology. In an infant with intussusception, prostration mimicking severe ‘weakness’ and lethargy may be the only presenting sign. When one comes to exposure in the primary survey of the weak child a thorough search has to take place for ticks (don’t forget to look in deep skin folds), possible venomous bites and stings, and rashes, such as those caused by enteroviruses. Enteroviral rashes are usually scattered maculopapular but may be petechial. A close inspection should be made for bruises and other suggestive signs of NAI. A quick assessment of the child’s nutritional state and the appropriateness of weight for age should be estimated. The size of the child’s head and its proportion to the body should be noted and centiles should be plotted later in the detailed examination phase.

ABC

The effects of weakness may include airway compromise from bulbar palsy (e.g. hoarse voice, stridor, and aspiration of secretions). Severely impaired ventilation will be clinically apparent. However, mild or moderate impairment can be subtle and can rapidly progress to cause respiratory embarrassment. Therefore, if possible, respiratory function tests should be serially performed on all children presenting with neuromuscular weakness. Arterial or venous blood gases should also be considered in this assessment. (Table 8.4.1 for predictors of needing intubation and mechanical ventilation.) Circulatory defects may arise from disturbance of the autonomic nervous system. This is characterised by labile blood pressure, heart rate and postural hypotension.

Table 8.4.1 Predictors of the necessity for ICU/HDU admission

Bulbar palsy Vital capacity <20 mL kg–1 >30%reduction in vital capacity from baseline Flaccid quadriparesis Rapidly progressive weakness Autonomic cardiovascular instability

Disability

The neurological part of the primary survey can give early hints as to the site of the lesion(s) involved. The classic description of peripheral neuromuscular weakness is an alert, but anxious looking, child that has a paucity of limb movements. If respiratory failure or facial weakness have intervened this appearance will not be present. Conversely, intracranial causes of weakness are usually associated with some degree of obtundation.

The weak infant classically lies in a frog leg posture with all limbs lying on the bed, abducted at the hips and flexed at the knees. Asymmetry may be apparent in those with a focal weakness. With central causes of weakness (e.g. acute hydrocephalus) hypertonic posturing may be seen, with scissoring adduction of lower limbs. Autonomic dysfunction may lead to associated fever or hypothermia. In any child with weakness one needs to consider whether the findings could be caused by a toxidrome (e.g. organophosphate poisoning).

Once the primary survey has been completed, and any abnormalities corrected, then a detailed history and examination should be performed.

History

If, on questioning, the weakness has been chronic then the list of possible diagnoses is extensive and is beyond the scope of this text. Such children should be stabilised and referred to the appropriate paediatric service for diagnosis. However, it is possible that a child with chronic weakness could undergo an acute deterioration, such as influenza in a child with a Duchenne muscular dystrophy. In infants the distinction between acute and chronic weakness is less relevant. In those children with conditions covered by this chapter, the history needs to focus initially on finding treatable causes. Detailed enquiry should be made about any possible tick bites or other venomous bites or stings. Enquiry should also be made about the availability of various medications and poisons around the house.

A precise time course for the illness should be obtained, along with the pattern of evolution of the weakness. Whether it is ascending from lower limbs up, whether it is lateralised and whether it has progressed or not. A sudden onset may suggest a vascular or epileptic event. Rapid onset weakness may follow an intoxication or envenomation. Other causes are more subacute and may have progressed over weeks. The family history should be reviewed, and whether there is consanguinity. A history of recent infectious illnesses may be relevant. Immunisation history regarding polio vaccination is important and diphtheria is still a common cause of weakness in third world countries. Any overseas travel should be noted.

Examination

A detailed but focused examination is then performed, that attempts to establish the level and the nature of the lesion. The following lists the important distinguishing features of the different levels of the neuromuscular system which may present with weakness.

Muscular:

• usually proximal more than distal weakness;
• reflexes preserved until very late;
• may have tender muscles;
• these children often have a positive Gower’s sign (see below).

Neuromuscular junction:

• fatigability;
• reflexes are preserved if the muscle is not fatigued or the disease is not severe.

Lower motor neuron weakness:

• more peripheral than proximal weakness;
• reflexes are lost early in the illness.

Upper motor neuron weakness:

• apart from an initial flaccid phase, tone and reflexes are usually increased;
• spinal cord lesions are usually associated with a sensory level;
• intracranial problems are associated with features of encephalopathy, decreased level of consciousness, speech dysfunction, ataxia, and bulbar dysfunction.

It may be difficult to perform a formal neurological examination in an unco-operative infant or small child. Often in these situations, one can get a lot of information just by watching the child play. Another useful test is known as Gower’s sign. The child is laid on their back on a firm surface and encouraged to stand. A child with proximal muscle weakness will not be able to sit up but will have to roll on to its abdomen get up on all fours and then ‘climb up its legs’ using its hands. Although reflexes are a good guide they are by no means foolproof. Upper motor lesions will usually have increased reflexes with increased tone. However, immediately after a spinal cord insult there may be a flaccid paralysis below the level of the lesion with absence of reflexes. Also, in transverse myelitis, there may be patchy combinations of upper and lower motor neuron signs. Early in Guillain–Barré syndrome the reflexes may be preserved and, likewise, very late in myopathic weakness, distal reflexes may be lost. Acute myositis is usually associated with tender muscles.

Investigations

Laboratory

Tests that may be useful in the acutely weak child include:

• a full blood count, which may reveal anaemia, nutritional disorders, leukaemia, or signs of infection;
• abnormalities of electrolytes especially potassium, calcium, phosphate, sodium may cause weakness;
• urea and creatinine – renal failure may present as generalised weakness, but more likely cause an abnormality of electrolytes;
• creatine kinase is often raised in muscular causes of acute weakness;
• endocrine function tests – especially thyroid and adrenal (see below);
• lumbar puncture (see below)
• electrophysiological studies (electromyogram (EMG), electroneurogram (ENG)).

Imaging

• Urgent magnetic resonance imaging (MRI) of spine (where progressive spinal cord lesion is suspected);
• Computerised tomography (CT) or MRI of brain (where central cause is suspected);
• Chest X-ray (e.g. for suspected aspiration).

Specific conditions causing acute weakness

Though not exhaustive, the following sections give some detail on the more common causes of acute weakness seen in children and also the rarer ones that must be diagnosed and treated in emergency.

Guillain–Barré syndrome

Introduction

Guillain–Barré syndrome (GBS) is an acute polyradiculopathy. It is now considered a group of diseases with two main pathological mechanisms; demyelination and axonal degeneration. In the paediatric population it is more common in late childhood (4–9 years of age) and in males (1.5 times higher risk). It is uncommon, estimated at less than 1/100 000 person years in people less than 17 years of age. It is primarily a lower motor neuron disease affecting the myelin sheath with variable damage to axons. It is an immune-mediated reaction, usually to a recent infection. Antibodies to various gangliosides are found in the serum of patients with GBS and matching antigens are often found in the preceding infectious agent. Infections known to be associated with GBS include Campylobacter, Mycoplasma, Epstein–Barr virus, Coxsackie viruses, influenza viruses, echoviruses and cytomegalovirus. The greater the axonal damage, the longer and the less complete is the recovery.

History and examination

Children usually present with weakness, falls, regression of motor milestones or ataxia. They also complain of muscle pain in the early part of the illness. Cranial nerves are involved in 40–50% of cases, with the facial nerve most commonly involved. The Miller–Fisher variant presents with oculomotor palsies, ataxia and areflexia.

On questioning, the parents often give a history of a generalised viral, respiratory or gastroenteritis illness in the preceding 2 weeks. In the early part of the illness the child may have paraesthesiae. Classically, the paralysis is ascending and symmetrical. The majority present with mostly distal weakness; however, about 15% have extensive proximal muscular involvement.

Papilloedema is rare, but may occur in GBS and is associated with raised intracranial pressure. Paralysis of the respiratory muscles is common and must be monitored carefully. Sympathetic nervous system involvement can produce profuse sweating, hypertension, postural hypotension and disturbances of sphincter function. Fatal cardiac arrhythmias have been reported in association with these signs. Although primarily a motor problem, sensory disturbance does occur, especially impairment of position sense. As mentioned above, reflexes are usually absent though increased reflexes and extensor plantar responses are occasionally found in the early phase of the illness.

The weakness may evolve rapidly within hours. However, it usually takes 1–2 weeks to reach the maximal weakness. Then, in the 2nd to 4th week of the illness, recovery is apparent and most children have recovered by 2 months, although some take as long as 18 months. Rarely, GBS will present in the newborn and is known as congenital GBS. They present as floppy babies that are areflexic and have elevated cerebrospinal fluid (CSF) protein.

Laboratory findings

An isolated elevation in CSF protein is the characteristic clinical finding of GBS. The CSF cell count is usually normal, although 5% of children may have a pleocystosis of 100 or so cells. Approximately 10% of children will have a normal CSF protein. The protein may be raised if a lumbar puncture is done later in the illness as it rises to a maximum after 4–5 weeks. The ENG characteristically shows conduction block, although this may not become apparent until weeks into the illness.

Differential diagnosis

As laboratory tests may be normal in early GBS and signs may be variable, it is important to exclude other causes of acute weakness (Table 8.4.2).

Table 8.4.2 Differential diagnosis of GBS

Diagnosis Features/action to exclude Puffer fish, Shell fish and Blue ringed octopus poisoning, Ciguatera History of ingestion or bite often a descending paralysis Tick paralysis Thorough examination of hair/skin creases Snake envenomation History; check for bite site; coagulation screen, creatine kinase Spinal cord lesion Look for upper motor neuron/mixed features and a sensory level; if suspected perform MRI Periodic paralysis Usually a sudden or very rapid onset, reflexes are diminished but preserved; check family history; measure serum potassium; do ECG Infant botulism Almost exclusively in infants; ask for history of eating honey; culture stools for Clostridium botulinum and test for botulinum toxin Poisoning (e.g. organophosphate, lead) History of exposure; toxidrome; check levels where suspected Myasthenia gravis Often cranial nerves involved; fatigability; look for antibodies; perform Tensilon test Vasculitis (e.g. polyarteritis nodosa) Check urinalysis; look for autoantibodies if suspected Myositis (e.g. dermatomyositis) Reflexes preserved; no ophthalmoplegia; look for characteristic rash; check creatine kinase; EMG Poliomyelitis, diphtheria, other enteroviruses Usually has fever and sore throat in diphtheria; ask about immunisations; no sensory changes

Treatment

The main role of the emergency physician in the treatment of GBS is in monitoring, prevention and treatment of cardiovascular and respiratory complications. In addition to monitoring of vital signs and cardiac rhythm, frequent examinations and (if possible) lung function tests should be performed. As noted above, progression to respiratory failure can be surprisingly rapid and the indicators for intubation listed in Table 8.4.3 should be actively sought to avoid respiratory arrest. The other less emergent treatments of GBS are either intravenous immunoglobulin or plasma exchange. This is indicated if the child can not walk unaided, has bulbar palsy, has rapidly progressive weakness, or worsening respiratory status. The immunoglobulin dose is usually 2 g kg–1 given in divided doses with variable regimes.

Table 8.4.3 Predictors of the necessity for intubation and ventilation in GBS

Vital capacity ≤20 mL kg−1 Maximum inspiratory pressure ≤30 cmH2O Maximum expiratory pressure ≤40 cmH2O Tidal volume <5 mL kg−1 A sustained increase of pCO2 to ≥50 mmHg An increasing respiratory rate Increasing oxygen requirement An increased use of accessory muscles and paradoxical diaphragm movements; these reflect restrictive lung-chest wall movement and low lung volumes

Prognosis

Prognosis is usually good in those treated and supported appropriately. Most children reach maximum weakness in 2 to 4 weeks then remain stable for 1–3 weeks and then recover fully over a period of time that varies from 6 weeks to many months. Approximately 85% of children recover completely. Mortality is 2 to 4% and is due to cardiovascular and respiratory complications.

Disposition

Children with suspected GBS should be admitted and closely observed for the evolution of severe weakness that can occur. The findings outlined in Table 8.4.1 will assist in deciding who should go to an intensive care unit (ICU)/high dependency unit and who should go to the general ward. Children with any one of these features should be monitored in a paediatric ICU.

Tick paralysis

Ticks that can cause paralysis are found throughout the world. In Australia Ixodes holocyclus is the main paralysing tick; it is found on the east coast. Other ticks have been known to cause paralysis, but they are rare. The toxin previously called holocyclotoxin is now thought to be several toxins. The toxins inhibit the release of acetylcholine from motor end plates. The paralysis usually occurs 5 to 7 days after the tick attaches. The paralysis can resemble GBS in the form of an ascending paralysis and is an important differential diagnosis because removal of the tick is necessary for recovery. The envenomation most frequently presents with cranial nerve palsies. Although the tick is often located in the vicinity of the palsy, this is not always the case and in all cases a thorough examination should be made for multiple ticks. The paralysis can be severe and require ventilation. Australian tick paralysis may get worse in the 48 hours following tick removal, and children should be monitored carefully during this time. Conversely, with children presenting with paralysis one should ask if a tick was removed in the last 48 hours. Deaths have usually been due to respiratory paralysis; however, there have been reports of myocarditis and autonomic effects on the heart. Treatment includes supportive therapy then careful removal of the tick(s) ensuring that the mouthparts are removed along with the body. This can be made easier by applying a pyrethrum spray, which suffocates the creature and makes it loosen its grip. Squeezing the tick is not recommended as this may inject more toxin. Human Tick Antivenom is no longer available. The treatment of tick paralysis is supportive; this may well include intubation and ventilation for several days after tick removal.

Other envenomations

Snake and spider bites are discussed in detail elsewhere in the text (see Chapter 22.1). Usually the history and accompanying symptoms will give the diagnosis. Death adder envenomation is usually a purely neurological presentation so in the weak non-verbal child a thorough look for a bite site is indicated.

Botulism

Poisoning with botulinum toxin can present in three ways:

Infant botulism;
Food-borne botulism; and
Wound botulism.

Infant botulism

Although rare, several cases of infant botulism have been reported in Australia in the last few years. Infant botulism is caused by release of botulinum toxin into the bloodstream from Clostridium botulinum bacteria colonising the intestines. Part of the toxin enters the terminal bouton of cholinergic motor nerves and enzymatically disables the mechanism by which acetylcholine-containing vesicles attach to the cell membrane. This process is irreversible and recovery occurs by sprouting new unmyelinated motor neurons. Risk factors for babies contracting this disease include exposure to honey in the first six months (honey is not recommended for babies under 1 year), decreased frequency of stooling and lack of breast-feeding.

Diagnosis of this condition is characterised by:

• age group – the infants are almost always less than 6 months; however, there are reports in infants up to 1 year and older children with abnormal bowel anatomy;
• nature of onset – the infants always start with bulbar palsies because that is where the blood supply is greatest; this is a descending paralysis;
• fatigability, but lack of reversibility with edrophonium or neostigmine;
• absence of fever;
• absence of an altered mental status;
• absence of sensory defects;
• normal CSF.

Clostridium botulinum may be cultured from the stools and the toxin may be found in stools or serum through polymerase chain reaction or enzyme-linked immunosorbent assay tests. Mouse bioassay is also available where sterilised stools are injected into a mouse to see if it becomes paralysed. If suspicion is high, foods in the child’s residence can be tested for C. botulinum. The EMG is characteristic.

The difficulty is in early diagnosis. A weak suck is often put down to generalised illness and it is often only the mother who notices the lack of expression on the infant’s face. A high index of suspicion needs to be maintained.

Treatment is by supportive care and administration of botulinum antitoxin. Antibiotics are not recommended unless there is secondary infection (e.g. pneumonia). This is because they may increase toxin release when the bacteria lyse and divulge their contents. Tube feeding is recommended as it restores peristalsis, which is essential for clearing C. botulinum from the gut. If antibiotics are used, aminoglycosides should be avoided because these worsen the paralysis. About half of the patients end up needing intubation and ventilation. Hospital stay is an average of 1 month but varies widely. Infants seem to recover completely.

There are two antitoxins available. Equine-derived antitoxin, a small amount of which is held in the Commonwealth Serum Laboratories, and botulism immune globulin (BIG), a human-derived hyperimmune globulin, which in a recent randomised controlled trial reduced hospital stay from 6.6 weeks to 2.6 weeks. It is not available outside the United States.

Food-borne botulism

This is due to consumption of food in which there is preformed toxin. It is associated with home-canned foods. It differs from infant botulism in that it can occur in any age group and one third of cases have gastroenteritis-like symptoms. The illness usually begins about 18 to 36 hours after ingestion, but onset can range from 2 hours to 8 days. Presentation is similar to infant botulism but more obvious because of the patients’ greater age. The treatment is similar.

Wound botulism

This is perhaps the rarest form. The differences from the other forms are the presence of a wound, which may be obviously infected, and the presence of fever. The incubation period is 4–14 days. This requires aggressive treatment with antibiotics and antitoxin.

Spinal cord lesions

These are usually distinguished from peripheral nerve disease by upper motor neuron signs. However, in many cases initially the reflexes and tone are diminished (e.g. ‘spinal shock’ after trauma). In other cases, there may be patchy upper and lower motor neuron involvement such as in transverse myelitis. Therefore spinal cord lesions need to be considered in the differential diagnosis of the weak child. The key to spinal cord lesions is the presence of a sensory level. However, in transverse myelitis and in a preverbal child this may be difficult to establish. If a spinal cord lesion is suspected, the investigation of choice is an urgent MRI. This is time-critical as a space-occupying lesion in the narrow canal can rapidly cause permanent damage to the surrounding cord.

Transverse myelitis (TM)

The aetiology of this acute spinal cord inflammation is still uncertain. Hypotheses include microbial antigen cross-reaction with neural elements, bacterial superantigen inflammation and direct microbial invasion. Rarely, it is associated with systemic diseases such as systemic lupus erythematosus and multiple sclerosis. It is likely that TM will be found to be several diseases and perhaps treatment will need to be tailored to the specific aetiology.

This disease usually has a rapid onset of predominantly lower limb weakness and altered sensation. Neck stiffness and fever are present early in most cases along with low back pain or abdominal pain. The sensory level is usually around the mid-thoracic region below which pain, light touch and temperature sensation are impaired. However, joint position and vibration sense are more preserved. Bladder and bowel disturbance is common, although this may be difficult to determine in a child in nappies. Tone is usually flaccid early in the illness with decreased reflexes, followed by increased tone and hyperreflexia as the disease progresses to its peak over the next 2–3 days. Sixty percent of patients recover fully over weeks to months.

Urgent MRI usually shows fusiform oedema around the site of the sensory level. CSF shows a moderate lymphocytosis and mildly raised protein.

Treatment is controversial, with case-control studies indicating a benefit with glucocorticoids, whereas prospective trials show no benefit. Treatment decisions should be made in consultation with a paediatric neurologist.

Spinal cord trauma

This is discussed in Section 3.

Spinal cord space-occupying lesions

These include epidural abscess, tumours, syringomyelia and arteriovenous malformations. Since syringomyelia is almost always a chronic condition it will not be dealt with here.

Tumours

These may be intramedullary (e.g. low-grade astrocytoma), extramedullary intradural (e.g. meningioma) and extradural (e.g. lymphoma). They usually have a more gradual onset than the other diseases mentioned in this chapter but the early signs may be missed and the child may present when signs are rapidly evolving due to high intramedullary pressures. Progressive gait and bladder disturbance with back pain and absence of fever are characteristic signs. Recent onset of scoliosis may be a feature. There may be a mixture of signs with upper motor neuron signs in the lower limbs and lower motor neuron signs in the upper limbs.

Urgent MRI is the investigation of choice, followed by consultation with surgeons and/or radiation oncologists. If MRI is unavailable, CT or plain X-ray may show abnormalities. However, these should only be done if they do not delay transfer to an MRI capable centre.

Arteriovenous malformations

These are usually in the thoracic region. They may cause symptoms as a space-occupying lesion causing compression or by stealing circulation from the nearby cord. The history is usually subacute, unless a haemorrhage or ischaemia has intervened. Clues to the diagnosis on examination include a cutaneous angioma over the region and a bruit on auscultation. MRI/MR angiogram will give the diagnosis but angiography is usually required to define the lesion fully and to decide on whether to treat with surgery or embolisation.

Epidural abscess

This is a rare disease in children, who usually present with back pain and rigidity, fever, leucocytosis and a raised erythrocyte sedimentation rate. These symptoms may be followed by spinal neurological signs. MRI is the investigation of choice, but there is controversy over whether treatment should be by surgery or antibiotics alone.

Tethered cord/diastematomyelia

These are two conditions that tend to fix the cord of the child, which has to ‘move up’ the canal as the child grows. They rarely present with acute weakness, although there may be sudden exacerbations on flexion and extension. Examination over the spine may reveal sentinel lesions such as a tuft of hair, a sacral pit, a lipoma, or a cutaneous haemangioma.

Myasthenia gravis (MG)

This condition, which is usually due to acetylcholine receptor autoantibodies, leads to easy and rapid fatigability of muscles. This may occur in children in three forms.

Transient myasthenia of newborns

This occurs where the mother has myasthenia. Maternal antibodies to the acetylcholine receptor (AChR) cross the placenta and the baby is born with fatigable muscle weakness. These babies may show very little motor activity for days after birth. Alternatively, they may just have feeding difficulty that worsens during the day. This illness improves within weeks as the maternal antibody levels diminish in the child’s blood. The only treatment is supportive by tube feeding and intubation and ventilation, if severe. The babies recover completely and have no increased risk of MG.

Congenital myasthenia

This is a lasting condition due to a genetic disorder. It is not due to antibodies to the AChR.

Acquired myasthenia

The incidence of this is low, though not insignificant. In an Italian study the annual incidence was 3.3 per million children <15 years; about 1% of total MG cases. The presentation is usually with ptosis, ophthalmoplegia or bulbar weakness. The clue on history is the worsening of symptoms as the day progresses due to fatigue. Peripheral muscles, especially limb girdle and hand muscles, are also involved. Reflexes are preserved but diminished. Clinical tests for fatigability such as getting the child to look up for 60–90 seconds and watching for ptosis, or to flap one arm ‘like a bird’ for a minute and then comparing its strength with the other arm are very useful.

Diagnosis can be made with three tests. First, an anticholinergic drug may be given. Edrophonium, the usual drug used in adults may cause cardiac arrhythmias in small children, so neostigmine is preferred. Atropine is given beforehand to block the muscarinic effects. These drugs should abolish the fatigability. Second, the EMG is characteristic and usually obviates the need for muscle biopsy. Third, AChR antibodies can be measured in the blood. Early diagnosis is important because, if untreated, this disease will often progress to life-threatening severity.

Associations with MG commonly found in adults, such as thymoma, are rare in children. Differential diagnosis includes botulism, chronic low-grade organophosphate toxicity and tick paralysis.

In the ED the child may present as an initial episode or because of a crisis of weakness. These crises may be myasthenic, due to exacerbation of the underlying condition or cholinergic due to excessive anticholinesterase treatment, which leads to over stimulation and exhaustion of receptors. Classically, a cholinergic crisis has the cholinergic toxidrome features of hypersalivation, pulmonary oedema and muscle fasciculation. However, in someone with myasthenia the cholinergic crisis may only be manifest by weakness. Distinguishing between a myasthenic and cholinergic crisis may be difficult. History may give a clue if medications have been missed or an overdose of pyridostigmine has been taken. A therapeutic trial of edrophonium may help, but should not be undertaken if there is significant risk of a cholinergic crisis. In the latter case supportive treatment and measurement of blood cholinesterase activity may be the only option.

Long-term treatment of MG comprises anticholinesterases and a variety of immunosuppression, IgG infusion or thymectomy.

In MG:

• Do not give neuromuscular blocking agents (e.g. suxamethonium, vecuronium) as these may paralyse the MG patient for days or even weeks.
• Do not give aminoglycoside antibiotics as these exacerbate the weakness.

Poliomyelitis and other enteroviral infections

Poliomyelitis is now exceedingly rare; however, one should always ask about immunisation status in the acutely weak child. If the child is not immunised one should ask about contact with infants recently immunised with Sabin (oral weakened live poliovirus) vaccine. Infants excrete the virus after the immunisation and this is where most recent cases of poliomyelitis have come from. The other source of infection is in developing nations, where immunisation rates are low. The illness itself usually presents with symptoms related to the virus’s portal of entry through the gut and upper respiratory tract. Patients have fever, sore throat, anorexia, nausea, vomiting, generalised non-specific abdominal pain, malaise and headache. The great majority of poliovirus infections end here or are asymptomatic. In those patients who progress there is often an asymptomatic period of 1–2 days followed by symptoms of aseptic meningitis with neck and often entire spine stiffness. There may be mild transient neurological deficits such as bladder paralysis and loss of abdominal and anal reflexes. Those who progress to paralytic polio will usually do so 8–12 hours after the superficial reflexes are lost. Poliovirus can infect and destroy neurons from the motor cortex down to the anterior horn cells. However, most commonly the paralytic form presents with patchy asymmetrical lower motor neuron weakness. Bulbar weakness is also a frequent presentation and often the picture is mixed. Rarely there are also encephalitic and ataxic presentations.

Diagnosis is based on the immunisation history, the clinical picture and a lumbar puncture showing a moderate pleocytosis, initially of neutrophils but then changing to monocytes. Serology and culture of stool, throat swab and rarely CSF will often reveal the organism. Treatment is supportive only. Infection control authorities need to be informed.

Bell’s palsy

A sudden or rapid onset of a unilateral lower motor neuron palsyis not a rare occurrence in children. Estimated annual incidence varies from 3 to 10 per 100 000 children per year. Its aetiology is uncertain. The disease commonly begins 2 weeks after an infectious illness, which suggests a post-infectious autoimmune or allergic aetiology. Lyme disease has been associated and serology should be done if the patient has been in an endemic area. Epstein–Barr, mumps and herpes simplex viruses have also been associated with this disease. An association with hypertension has suggested another aetiology related to pressure necrosis of the nerve due to swelling in the narrow facial canal.

The patient often presents with pain around the ipsilateral ear and may also complain of abnormal hearing. About half have loss of taste sensation to the anterior two-thirds of the tongue and there may be hemifacial ‘dysaesthesia’ due to the proprioceptive fibres to the facial muscles in the facial nerve.

The differential is extensive but the diagnosis can be determined by a thorough history and clinical examination. One should look for evidence of trauma (be aware of non-accidental injury), central nervous system dysfunction, aural lesions (e.g. the Ramsay Hunt syndrome), other cranial nerve dysfunctions, hypertension and GBS. Acute lymphoblastic leukaemia and even sarcoidosis have been reported.

Treatment is controversial, as the prognosis in children is better than in adults. Complete recovery occurs in 60 to 80% of patients, with near complete recovery in the remainder. In one study average time to recovery was about 7 weeks with a range of 9 days to 7 months. Uncontrolled studies have claimed a benefit for early corticosteroid therapy. However, controlled studies in adults have shown a benefit for oral glucocorticoids in Bell’s palsy. This and the less reliable evidence in children prompt this author to recommend glucocorticoids in all but the mildest cases of Bell’s palsy. There is even less evidence for antiviral agents in the absence of apparent viral infection (e.g. the Ramsay Hunt syndrome). If the eyelid does not completely close steps should be taken to protect the cornea from exposure keratopathy, i.e. artificial tears and eyeglasses during the daytime, ointment and a protective eye chamber at night.

Toxic neuropathies

A long list of substances can cause acute weakness. Some of the more common ones are listed here.

Anticholinesterases

The organophosphates and carbamates are commonly used insecticides, which can cause poisoning through skin, oral or pulmonary exposure. They inhibit cholinesterases, allowing acetylcholine to persistently stimulate the nicotinic and muscarinic receptors, which then can become refractory and thus cause weakness. This weakness is usually accompanied by the cholinergic toxidrome (see Chapter 21.2 on toxicology) and, indeed, it is usually the respiratory and cardiac features that predominate. However, there is an intermediate syndrome where 12 hours to 7 days after the initial poisoning, one finds proximal limb weakness that is unresponsive to atropine or pralidoxime. There may also be respiratory and bulbar paralysis. Recovery from this is usually complete. Late neurotoxicity arises 4–21 days after the acute exposure, causing a mixed sensory motor deficit, which may take weeks or months to recover, or may be permanent. Diagnosis is by identification of the poison at source or in urine or serum drug screens and also by measuring serum cholinesterase activity level. Treatment is supportive and with antidotes atropine and pralidoxime. Muscle relaxants will have a prolonged effect and should be avoided if possible.

Lead and other heavy metals

Lead, mercury and arsenic are all known to cause neuropathies, often taking the form of mononeuritis multiplex. It is uncommon for these to present as acute weakness. Nevertheless, a history of exposure should be sought and appropriate specimens taken if the cause of the acute weakness is unclear.

Chemotherapeutic agents

Vincristine, vinblastine and cisplatin are known to cause a peripheral neuropathy. Any child who is on, or has recently had, chemotherapy needs to have this ruled out as a possible cause.

Hereditary neuropathy

Rarely, a patient with an undiagnosed hereditary neuropathy presents with an acute exacerbation. A thorough history will reveal the chronicity of the problem. Such patients should be referred to an appropriate paediatric neurology service.

Muscular disorders

Juvenile dermatomyositis

Juvenile dermatomyositis is a systemic vasculitis thought to be triggered by infection. Both enteroviruses and Group A Streptococcus have been implicated. This is the most common myositis of childhood. Its peak age of incidence is 6 years. Because of its gradual onset this uncommonly presents as acute weakness. The child may well present with the rash before weakness has become apparent.

The rash appears on sun-exposed areas, especially the malar region of the face and a purple discolouration of the eyelids is apparent (heliotrope rash). The rash may also be found on the extensor surfaces of the arms and legs, thorax, ankles and buttocks. The fingers develop thickening of the skin over joints, called Gottron’s papules. The weakness comes on about 2 months after the rash and is usually very slow in onset. Small children may be noted to become gradually inactive and older children have increasing difficulty with sport. Proximal muscle activities, such as climbing up stairs, reveal the weakness first. The vasculopathy can affect any muscle group and children may present with aspiration dysphagia or hoarse voice due to pharyngeal muscle weakness. The affected muscles are often tender and sometimes swollen.

The vasculitis can affect any organ system. Subclinical myocarditis and conduction defects are often found at diagnosis. Less common effects include renal dysfunction, hepatosplenomegaly, retinitis, iritis, seizures, depression, bowel dysfunction and pulmonary disease.

Diagnosis is made on the clinical picture associated with a raised serum creatine kinase. There are typical changes on muscle biopsy and electromyogram. There may also be elevated autoantibodies, liver function tests and abnormalities on MRI.

Complications include calcinosis of muscles, subcutaneous fat and fascia. These are more likely if the illness is prolonged and are decreased by aggressive treatment. Calcinosis lesions may become infected and lead to septicaemia.

These children may require judicious use of pain relief and require referral to a specialist paediatric unit. Treatment options range from sunscreen for the rash through to immunosuppression with glucocorticoids and chemotherapeutic agents, depending on the severity of the disease. Prognosis is generally good in children, with approximately 80% making a good recovery.

Infectious myositis

Viral infections such as influenza can uncommonly cause a myositis that may in its severest form lead to rhabdomyolysis and myoglobinuria. Various bacteria including Streptococcus and Mycoplasma species have been reported to cause a focal myositis with tender muscles. These usually present with the other features of the infection and myalgia, rather than acute weakness. The weakness is only found on close examination, if the myalgia permits. The creatine kinase is raised. The prognosis is generally good although permanent muscle damage may ensue, especially in focal bacterial myositis.

Metabolic/endocrine myopathies

Most endocrinopathies can produce weakness by several mechanisms. Often this is just myalgia and fatigue, but true myopathies can develop. This weakness usually responds to the treatment of the underlying endocrine disorder. Endocrinopathies can be associated with electrolyte disturbances that lead to weakness (e.g. hypokalaemia in Conn’s syndrome) or with primary muscle diseases, such as hypokalaemic periodic paralysis with thyrotoxicosis.

The periodic paralyses are a series of genetic ion channel disorders that lead to acute episodes of weakness lasting from 1 hour up to more than a day. They often come on after rest, during sleep or following exercise, but never during exercise. Diagnosis is by measurement of electrolytes during an attack or response to a metabolic challenge or by gene mutation identification. Hypokalaemic periodic paralysis usually occurs in adolescence. The patient will have low potassium during attacks. Conversely, hyperkalaemic periodic paralysis usually comes on in early childhood. The attacks are more frequent, occurring up to several times a day and are associated with an elevated or normal potassium. The identification of these diseases is important, as they are treatable.

Somatisation disorders/malingering

Occasionally, children may present with a psychogenic cause of weakness. The findings of a careful neurological examination will demonstrate inconsistencies and the child will be able to perform manoeuvres that require more strength than normal walking (e.g. knees giving way but not falling). Reflexes will be normal. Usually, no laboratory tests or imaging are necessary. However, if there is any doubt, consultation and investigation should be undertaken.

Once you have made the diagnosis it is best to take the parent or carer aside and discuss the diagnosis with them. Confrontation of the child is rarely helpful and it is often best to reassure the child that this is not serious and that they will get better. This gives the child an exit from the medical review with dignity intact. An effort should be made to find the underlying psychological reason for the presentation, which may be anything from school avoidance to sexual abuse. Consultation with social work or psychiatry may be indicated for ongoing counselling.

Further reading

Behrman R.E., Kliegman R., Jenson H.B., editors. Nelson Textbook of Pediatrics, 16th ed., Philadelphia: WB Saunders, 2000.

Emilia-Romagna Study Group on Clinical and Epidemiological Problems in Neurology. Incidence of myasthenia gravis in the Emilia-Romagna region: A prospective multicenter study. Neurology. 1998;51(1):255-258. [brief communications]

Lawn N.D., Fletcher D.D., Henderson R.D., et al. Anticipating mechanical ventilation in Guillain–Barré syndrome. Arch Neurol. 2001;58:893-898.

Odaka M., Yuki N., Hirata K. Anti-GQ1b IgG antibody syndrome: Clinical and immunological range. J Neurol, Neurosurg Psychiatry. 2001;70:50-55.

Tang T., Noble-Jamieson C. A painful hip as a presentation of Guillain-Barré syndrome in children. Br Med J. 2001;322:149-150.

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