Wilderness Neurology

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Chapter 33 Wilderness Neurology

Charles Clarke

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It is essential for practitioners in wilderness settings to have a working knowledge of neurology and to be able to diagnose and treat patients without recourse to specialist investigation, especially computed tomography and magnetic resonance imaging. Circumstances will vary depending on terrain, weather, and the availability of emergency transport (Figure 33-1, online).

FIGURE 33-1 Dr. Charles Clarke and Per Temba Sherpa treating a case of high-altitude cerebral edema at 6100 m (20,013 feet) on the British expedition of the southwest face of Mt Everest in 1975.

(Courtesy Dr. Charles Clarke.)

This chapter focuses on common neurologic problems. Important neurologic problems within wilderness medicine are divided into three main groups:

• Specific neurologic conditions that are the results of an extreme environmental stressor. Examples include cerebral edema in high-altitude mountaineers and trekkers; nitrogen narcosis in divers at great depths; and decompression sickness when surfacing after a dive. These conditions typically require specialist knowledge to recognize and treat, and they form an important group of neurologic emergencies. Conditions discussed in other chapters include high-altitude cerebral edema (HACE) and acute mountain sickness; diving medical emergencies; hypothermia; frostbite; nonfreezing cold injuries; heat-related illnesses; insect, plant, animal, and marine toxins; lightning strikes; carbon monoxide poisoning; and drowning.

• Incidental neurologic conditions that occur in a wilderness setting. Examples include migraine or tension headache, syncope or a suspected seizure, Bell’s palsy, meningitis, transient cerebral ischemia, stroke, head injury, and brain tumor. These are the primary subject matters of this chapter. When a diagnosis is not obvious, management can be difficult, and it tends to differ from practice in a clinical setting. If evacuation to a hospital is felt to be necessary, decisions can affect not only the patient but also their companions and sometimes the entire enterprise. Careful risk evaluation is essential.

• Advice and management related to preexisting neurologic conditions. Examples include handling recurrent seizures in known cases of epilepsy or advising whether or not a person should take part in a trek in a remote area when he or she has been previously diagnosed with multiple sclerosis.

Preliminaries: History and Examination

The majority of neurologic conditions can be diagnosed with the use of a minimum of tools with a combination of history, observation, and physical examination. Clinical diagnosis in neurology is highly reliable; in no other branch of medicine are disease patterns and physical signs more consistent and dependable.

This section outlines the rudiments of diagnosis, and stresses that a brief examination in combination with a succinct and practical formulation are essential. Written records should be maintained in all circumstances. In the event of any substantive illness and after any accident, one should inform the relevant insurance company, because many policies exclude coverage for late complications unless illnesses or accidents have been reported promptly. This holds true beyond neurology per se.

There is no substitute for a careful history from the patient, his or her companions, or witnesses. Until the practitioner learns the actual story of what happened, he or she should not jump to medical conclusions. For example, the person who has fallen to the ground while shaking has not necessarily suffered a seizure; there is a broad differential diagnosis.

Nervous system examination need not be lengthy or complex. A short neurologic examination (Box 33-1) takes less than 5 minutes. Much can be done without any special equipment; a tendon hammer can be improvised easily, and lack of an ophthalmoscope rarely makes a great difference to diagnosis and management.

Try to answer the following critical questions, using the story and examination findings:

• What are the sites of the lesions?

• What is the likely pathology?

• Does a recognizable disease fit this pattern?

• Broadly, is this really serious, and what is the sensible way going forward?

Pattern recognition—and thus some experience—is vital. Try to take matters as simply as possible, gauge whether or not the case is truly serious, and review physical signs regularly. In wilderness settings, one may only be able to reach tentative conclusions. The substantial majority of all neurology cases turn out not to be sinister, and fortunately there are few true neurologic field emergencies where immediate action is vital.

Incidental Neurologic Conditions

Diagnosing and Managing Headache

Headache is one of the most common symptoms in medicine and a frequent problem in wilderness settings. Its significance ranges from an infrequent and trivial problem to a persistent unpleasant symptom to a marker of serious disease. In wilderness practice, complex headache classifications are of little value.

Headache Mechanisms

Pain receptors are located at the base of the brain in the arteries and veins and throughout the meninges, extracranial vessels, scalp, neck and facial muscles, paranasal sinuses, eyes, and teeth. The brain itself is nearly devoid of pain receptors.

Head pain is mediated via mechanical and chemical receptors, including the stretching of the meninges as well as neurotransmitters such as 5-hydroxytryptamine and histamine and their receptors and pathways. Nerve impulses travel from the peripheral structures above via the fifth and ninth cranial nerves and upper cervical sensory roots, and they pass centrally through the thalamus to the sensory cortex. The vast majority of headaches are benign. However, the diagnostic issue is the question of serious disease.

Common Headache

Almost all headaches without other neurologic signs and with a duration of hours to days are of a band-like or generalized nature, often with a history of some weeks or a background history of several years. These headaches are usually the result of muscle tension or migraine. Migraine associates visual symptoms, nausea, and vomiting with the headaches. Emotional depression is common with any longstanding headache, but it is unwise to assume automatically that a psychological cause lies at the root of a headache.

Headaches are not caused by essential hypertension. Malignant hypertension or accelerated hypertension with hypertensive encephalopathy can cause headache, but this is a rarity.

Eye strain from refractive error does not itself cause headache. New prescription lenses sometimes provoke head pain, which is generally loosely regarded as being the result of eye strain and which is mediated via the pupils readjusting to a new refractive situation.

In wilderness settings in snow, at sea, or in the desert, ultraviolet radiation and glare cause headache. In snow, this is as a part of snowblindness; painful keratoconjunctivitis can develop. Acute mountain sickness is a common cause of headache above 3000 m (9843 feet), and it may be premonitory for HACE. Headache is also said by some to be a feature of dehydration.

Sudden Headache of Short Duration

If pain is focal (e.g., localized to the upper face and lasting minutes to hours), consider sinusitis, glaucoma, and cluster headache. The sudden headache associated with subarachnoid hemorrhage, severe migraine, bacterial meningitis, and cervical arterial dissection is discussed later in this chapter.

Headache Caused by Increased Intracranial Pressure

Intracranial mass lesions displace and stretch the meninges and the basal vessels. Pain is provoked when these structures are shifted either by a mass or by changes in cerebrospinal fluid pressure, such as may be caused by coughing. Cerebral edema around brain tumors causes the further shift of intracranial structures. Pressure headaches typically worsen when a patient is lying down or with movement; this feature is also seen commonly with migraine, acute mountain sickness, and HACE.

Many textbooks indicate that any new headache that is present on waking and made worse by coughing, straining, or sneezing may be the result of a mass lesion, but it should be noted that benign headaches (e.g., migraine) are often made worse with head movement. Vomiting often accompanies pressure headaches. Pressure headaches appear early during the pathologic process and over the course of days or weeks when they are caused by posterior fossa masses or hydrocephalus, but they typically develop over months or years when they are caused by hemisphere tumors. Pressure headaches with ataxia occur with HACE. A rare cause of prostrating headache with lower-limb weakness is an intraventricular tumor that causes intermittent hydrocephalus.

Headache of Subacute Onset

The onset and progression of a headache over days or weeks with or without features of a pressure headache should raise suspicion of an intracranial mass or serious intracranial disease. Encephalitis, viral meningitis, and chronic meningitis should be considered when a headache increases over the course of several days.

Headache with Scalp Tenderness

Patches of exquisite tenderness overlying superficial scalp arteries may be caused by giant cell arteritis (temporal arteritis) in patients who are more than 50 years old, and they almost never appear among younger persons.

Headache after Head Injury

The vast majority of headaches that occur after trauma—even those that last for several months—are not caused by serious intracranial pathology. However, subdural and extradural hematoma (see Chapter 21) must be considered in the aftermath of head injury. Both are rare in the absence of corroborating physical signs.

A Single Episode of Sudden Severe Headache

The common emergency of a single episode of sudden severe headache is caused by migraine or another benign type of headache (e.g., cluster), or it may be the result of serious events such as subarachnoid hemorrhage (SAH), cervical arterial dissection, or the onset of meningitis. The term thunderclap headache is used to describe such a devastating sudden headache without a clear cause. This is usually migrainous, but it also may indicate the onset of subarachnoid bleeding.

Particular attention should be paid to the sudden onset, which is suggestive of SAH. The mode of onset, time to peak, duration, associated symptoms, and the patient’s headache history should be explored. The patient with SAH usually will indicate precisely the time of onset of a sudden headache. High fever, neck stiffness, vomiting, meningeal irritation, and a rash suggest bacterial meningitis, which requires immediate treatment. For nonfebrile persons, careful reassessment over the course of 12 hours can usually sort out whether a sudden headache was a migraine or part of SAH. Bacterial meningitis is often obvious at the onset. Cervical arterial dissection is discussed briefly in this chapter (see Stroke, later).

Wilderness Guidelines for the Diagnosis of Headache

With any headache, first establish whether there is fever, a rash, or any “hard” neurologic signs, such as diplopia, papilledema, hemiparesis, or ataxia. If any of these is present, serious pathology must be considered. Papilledema may be difficult to detect with certainty in isolated circumstances. Easily visible retinal hemorrhages almost always accompany true disc edema. Consider the following questions:

1 Is this headache a migraine?

The development of sudden headache, no matter how severe, that involves flashing lights, nausea, and vomiting is very likely to be migraine. Some migraines are devastating. Subarachnoid bleeding does not typically cause migrainous visual symptoms. In any event, in wilderness settings, management is expectant, because immediate evacuation is unlikely to be possible. Treat the patient with an analgesic (e.g., acetaminophen) and an antiemetic (e.g., metoclopramide, ondansetron). Await and expect recovery. After 12 to 24 hours, the majority of migraines will have resolved. If the patient becomes drowsy with neck stiffness, subarachnoid bleeding should be considered.

2 Does the headache appear to be a tension headache or a chronic daily headache?

Band-like (i.e., around the head) headaches without any other clinical features and the absence of neurologic signs are distinctly unlikely to be the result of anything sinister. Again, await events.

3 Is the headache localized?

Sinusitis, glaucoma, dental pain, and cluster headache need to be considered. With glaucoma, the eyeball will typically be painful, and vision may be altered. Sinusitis can cause severe pain that is usually well localized within and around the infected sinus. Cluster headache causes pain of exceptional severity, often at night, and is typically perceived around and behind the eye. Cluster headache, no matter how severe, tends to resolve after 4 to 6 hours.

4 Are the headaches subacute (i.e., have they gradually worsened over days to weeks)?

This is a cause for concern and requires careful reevaluation for emerging physical signs. For example, in a situation that involves chronic meningitis (e.g., tuberculous meningitis), headache can precede the onset of neck stiffness and emerging signs (e.g., hemiparesis, cranial nerve lesions) by several weeks.

Blackouts and Episodes of Impaired Consciousness

The word blackout is used here as a general term to mean an episode of altered consciousness. Typically, no sinister cause is found, and simple syncope is the most common reason. In the United Kingdom, among persons who are initially diagnosed with a seizure in the emergency department or by paramedics, only about 20% have epilepsy. The differential diagnosis lies between vasovagal syncope, seizure, cardiac arrhythmia, nonepileptic attack disorder, and rarer causes of impaired consciousness.

Epilepsy

A seizure (i.e., a convulsion or “fit”) is caused by a paroxysmal discharge of cerebral neurons. Epilepsy is the continuing tendency to have seizures, even if a long interval separates the attacks. A generalized convulsion (i.e., a grand mal seizure) is the most common recognized event. More than 2% of the population in developed countries is known to have two or more seizures during their lifetimes; among 0.5%, epilepsy is an active problem. Around 200,000 people in the United Kingdom and around 1.5 million people in the United States take antiepileptic drugs.

Classification

The terms that are used to classify epilepsy include idiopathic, symptomatic, cryptogenic, primary generalized, focal (partial), and secondarily generalized. The clinical patterns of the main types of attack are described here.

A generalized (i.e., grand mal or tonic-clonic) seizure is a convulsion that involves bilateral motor manifestations (i.e., convulsive features) and a loss of consciousness. With a primary generalized seizure, the origin of the abnormal electrical spike-and-wave activity seen with electroencephalography during the event is bilateral.

A partial (focal) seizure occurs when the electrical abnormality remains localized to one part of the cerebral cortex. With a simple partial seizure, there is no loss of awareness (e.g., one limb jerking in a Jacksonian seizure). With a complex partial seizure, there is a loss of awareness (e.g., a temporal lobe seizure).

A secondary generalized seizure is a grand mal fit that began as a focal seizure.

Diagnosing a Seizure

Eyewitness accounts may be unclear and colored by the drama of the situation. Some stages of a seizure may be absent. With a primary generalized seizure, the typical stages are first the warning (i.e., a perception that something is about to happen but without a specific aura), which leads to the tonic (i.e., stiff or rigid) phase, during which the patient falls unconscious to the ground, sometimes first uttering a cry. Injuries are common, and the tongue may be severely bitten. Incontinence of urine, feces, or both may follow. The clonic (convulsive) phase begins, with bilateral rhythmic limb jerking and foaming at the mouth. This convulsive phase lasts from a few seconds to several minutes. The patient is typically cyanotic during the attack. Postictal drowsiness, confusion, or coma follows; this sometimes lasts for several hours, but it typically lasts for several minutes.

With a partial seizure, the sequence of events depends on the site of the seizure origin in the cortex. The patient may have an aura before the seizure begins. An aura is a specific and patterned sensation that is caused by a focal cortical electrical discharge.

With a simple Jacksonian partial motor seizure that has its origin within the motor cortex, the patient may sense a vague warning (as with a primary generalized seizure) that is followed by a specific aura (e.g., unusual sensations in one limb). This is followed by the onset of rhythmic jerking, typically in one hand or foot. Jerking spreads to the entire limb or to both the upper and lower limbs and possibly the face on the same side. This progression is known as the “march” of the seizure. Consciousness is not lost during a simple partial seizure. In place of postictal drowsiness or coma, weakness of the limbs that were involved with the seizure may follow. This is known as Todd’s paralysis, and it may last for several hours. A stroke may be suspected if early stages of the seizure were not witnessed or if they are unclear.

With a complex partial seizure of temporal lobe origin, the patient may experience an aura of familiarity with his or her surroundings, which is known as déjà vu; this is followed by an “absence attack” during which the patient is generally unaware or disoriented. As the seizure develops, the patient looks distant (i.e., appears to be in a trance-like state) and does not respond to stimuli. Facial or lip twitching may occur. Recovery is typically rapid, with the patient regaining full awareness in a matter of seconds or minutes (and rarely in more than 10 minutes).

A focal seizure may progress to become secondarily generalized. For example, a Jacksonian motor seizure may develop into a grand mal fit.

The usual differential diagnosis of a seizure is between syncope and a nonepileptic attack. There are many causes of loss of consciousness or sudden attacks; these are described later in this chapter. Assuming that one knows what to expect, they are usually recognizable.

Emergency Management of Seizures

In the field, a seizure may well take place in a sensational situation, such as on a glacier, on a steep path, on a climb, or at sea. The doctor’s actions are frequently very much in the public view, and there is often an expectation that skilled and urgent treatment must be seen to be underway. The reality is that careful observation is usually the most important activity.

Immediately establish and maintain a patent airway. Do not force the patient’s mouth open. Wooden mouth wedges, tongue forceps, and excessive restraint are likely to cause more injuries than will any seizure. Deep cyanosis is typical during a grand mal fit. The spontaneous return of normal breathing and oxygenation will remedy the problem.

If an attack lasts for more than a few seconds, stay with the patient, summon help, assist with breathing, and establish intravenous access, if possible. The latter is unlikely to be necessary, but it prepares the patient for the medical emergency of status epilepticus. Most seizures resolve spontaneously.

Status Epilepticus

Status epilepticus, which is also known as status (Box 33-2), involves the occurrence of continuous seizures (two or more) without fully recovering consciousness. More than 50% of cases of status occur without a previous history of epilepsy. Status is associated with a mortality rate of 10% to 15%.

BOX 33-2

Status Epilepticus

Before all else, do the following:

• Preserve and maintain the airway.

• Treat convulsions rapidly.

• Check for head and other injuries.

• Protect and stay with the patient.

• Establish intravenous access, if possible.

Drugs:

• Give diazepam (5-10 mg IV at 5 mg/min or less every 5-10 min to a maximum of 30 mg).

• Use rectal diazepam (10-20 mg) or buccal midazolam (10 mg repeated once after 10 min if intravenous access is impossible.)

• Order two people to act as assistants.

• Administer oxygen and monitor the pulse and blood pressure, if possible.

• Give intravenous glucose and thiamine.

If status epilepticus persists, consider other antiepileptic drugs:

• Lorazepam (4 mg at 2 mg/min IV every 10-15 min to a maximum of 8 mg)

• Phenytoin (intravenous bolus not exceeding 50 mg/min and an adult dose of 10-20 mg/kg)

• Phenobarbital (intravenous bolus of 60 mg/min or less and an adult dose of 10-20 mg/kg to a maximum of 30 mg/kg)

• Valproate (intravenous adult dose of 15-45 mg/kg at 6 mg/kg/min or less)

• Remember the potential unwanted effects of antiepileptic drugs, such as hypotension, cardiac dysrhythmias, and cardiorespiratory arrest.

• Continue to monitor the patient as best as possible

Doses from Clarke C, Howard R, Shorvon S, et al: Neurology: A Queen Square textbook, Oxford, UK, 2009, Wiley Blackwell Publishing, p. 235.IV, Intravenously.

Around 25% of patients with apparent refractory status have pseudostatus, which is also known as nonepileptic attack disorder (NEAD). Although the apparent status is factitious, there are great difficulties when it comes to making a confident diagnosis in this emergency situation.

Not all status is convulsive. With absence status, the patient is in a continuous, distant, and stuporous state. The term focal status

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