8.5 Acute ataxia
Introduction
Ataxia is an uncommon, but important paediatric presentation to the emergency department (ED). Ataxia is a disorder of movement manifest by the loss of coordination, most apparent as a disturbance of gait, with intact muscle strength. It may be associated with a disturbance of balance. Ataxia is most often caused by a loss of function of the cerebellum, which controls the coordination of movement. Disease of the peripheral sensory nerves or the spinal column, particularly affecting proprioception, may also lead to ataxia as a result of abnormal inputs into the cerebellum. Cortical ataxia results from cerebral cortical dysfunction, particularly of the frontal lobe, while vestibular ataxia results from disease of the inner ear. Rarely, psychiatric causes of ‘ataxia’ may also be seen as a manifestation of conversion reaction. The most common diagnosis of acute ataxia in children is a post-infectious ataxia called acute cerebellar ataxia (see below). This is a diagnosis of exclusion, made after consideration of other causes (Table 8.5.1). These include poisoning, metabolic disorders and organic brain lesion.
Differential diagnosis
Acute cerebellar ataxia
Acute cerebellar ataxia is the most common diagnosis in acute ataxia in children, particularly between 2 and 7 years of age. It is a diagnosis of exclusion, after consideration of more sinister causes such as tumours. An autoimmune aetiology is likely, with autoantibodies demonstrated in acute cerebellar ataxia following infections with varicella,1,2 Epstein–Barr virus (EBV),3 mycoplasma and human parvovirus B19.4 The clinical presentation is of a prodromal illness, frequently non-specific, with or without an exanthema, 5–10 days prior to the onset of acute ataxia, though the timing may show considerable variation. If a specific aetiology is present it is most commonly varicella,5 though a number of other viruses have been implicated (Table 8.5.2).6–22 Acute cerebellar ataxia usually presents with sudden onset of severe gait ataxia, though a small number of cases have an insidious onset. Most have dysarthric speech. Mild horizontal nystagmus occurs in 50% of cases. Findings of intention tremor, dysdiadochokinesis, hypotonia and decreased or pendular reflexes are seen in two-thirds of cases, but are less pronounced than the gait disturbance. Truncal ataxia is uncommon. Unlike acute disseminated encephalomyelitis (ADEM) or multiple sclerosis, there are no focal neurological signs.
Investigations are aimed at excluding an alternative diagnosis, if the diagnosis is unclear. The computerised tomography (CT) scan is normal in acute cerebellar ataxia; however, magnetic resonance imaging (MRI) may be abnormal. In one series, inflammatory changes were seen in the cerebellum of one of nine children.23,24 There is a slight elevation of CSF cell count by 4–50 cells per microlitre in 32%, though occasionally (in 8%) the elevation is higher. There may also be slightly elevated protein 410–900 mg L–1.25
Acute cerebellar ataxia usually begins to improve within a few days, but full recovery may take from 10 days to 2 months. Patients who have a slower recovery are still likely to recover fully. In one series, 91% recovered fully from their ataxia, including all those with varicella, EBV or post-vaccination, but 8% had sustained learning problems. Varicella-associated ataxia recovered quicker than non-varicella.24
Poisoning
Accidental poisoning occurs most commonly in 1 to 4-year-old children. A wide variety of compounds are implicated, including alcohols, substances of abuse and essential oils, as well as medications (Table 8.5.3). In addition to ataxia, these children may have nystagmus, altered mental status and vomiting. This is different to acute cerebellar ataxia where consciousness is unimpaired.
Anticonvulsants
Phenytoin toxicity with serum levels of >20–30 mcg mL–1 may produce signs of ataxia, nystagmus on lateral gaze and drowsiness. Onset of symptoms following an acute ingestion is usually within 1–2 hours and may persist for 4–5 days. At >30 mcg mL–1, the ataxia and drowsiness become more marked and the nystagmus vertical.26–28
Carbamazepine toxicity may also lead to ataxia. There are usually associated findings of drowsiness and nystagmus. There may be progression to seizures and coma, particularly if the level is >100 μmol L–1.29