Neurological disease

16 Neurological disease


The brain, spinal cord and peripheral nerves constitute an organ responsible for perception of the environment, a person’s behaviour within it, and the maintenance of the body’s internal milieu in readiness for this behaviour. In the UK some 10% of the population consult their GP each year with a neurological symptom, and neurological disorders account for about one-fifth of acute medical admissions and a large proportion of chronic physical disability.




CLINICAL EXAMINATION OF THE NERVOUS SYSTEM









MIGRAINE



Clinical assessment


Migraine is a triad of paroxysmal headache, nausea and/or vomiting, and an ‘aura’ of focal neurological events. Patients with all three features have migraine with aura (‘classical’ migraine). Migraine without aura, with or without vomiting, is called ‘common’ migraine. A classical migraine attack starts with a prodrome of malaise and irritability followed by the ‘aura’ of a focal neurological event, and then a severe, throbbing, hemicranial headache with photophobia and vomiting. The headache may persist for several days.


The ‘aura’ typically lasts 20–30 mins, and usually takes the form of ‘fortification spectra’: shimmering zigzag lines which march across the visual fields. Some patients experience a sensory aura: tingling then numbness moving from one part of the body to another. Patients may also experience transient aphasia. True weakness is distinctly unusual, so ‘hemiplegic migraine’ should be diagnosed with caution.


The aetiology of migraine is largely unknown.












DIZZINESS, BLACKOUTS AND ‘FUNNY TURNS’


Episodes of lost or altered consciousness are frequent. After a careful history from the patient, supplemented by a witness account, it should be clear whether the patient is describing loss of consciousness, altered consciousness, vertigo, transient amnesia or something else. The diagnostic approach is shown in Figure 16.1.









SEIZURES


A seizure is any clinical event caused by an abnormal electrical discharge in the brain, whilst epilepsy is the tendency to have recurrent seizures. The division of seizure types on physiological grounds is between partial (focal) seizures in which paroxysmal neuronal activity is limited to one part of the cortex, and generalised seizures where the electrophysiological abnormality involves both hemispheres simultaneously.



Clinical assessment


Tonic clonic seizures: These may be preceded by a partial seizure (the ‘aura’). The patient then goes rigid, stops breathing, becomes unconscious and cyanosed, and may fall. After a few moments, the rigidity is periodically relaxed, producing clonic jerks. Urinary incontinence or tongue-biting may occur. The patient then gradually regains consciousness, but is drowsy or confused for some hours.


Complex partial seizures: Partial seizures cause episodes of altered consciousness without the patient collapsing to the ground. The patient stares blankly, often making rhythmic smacking movements of the lips or other automatisms. After a few minutes the patient returns to consciousness but may be muddled or drowsy. Immediately before the attack there may be alterations of mood, memory and perception. If these occur without subsequent alteration in awareness, the seizure is a simple partial seizure.


Absence seizures: These are generalised seizures which always start in childhood. The child goes blank and stares for a few seconds only. The attacks resemble complex partial seizures but are usually shorter, more frequent and not associated with post-ictal confusion.


Partial motor seizures: Epileptic activity in the pre-central gyrus causes partial motor seizures affecting the contralateral face, arm, trunk or leg. There is rhythmical jerking or sustained spasm of the affected parts. They may remain localised to one part, or may spread to involve the whole side. Some attacks begin in one part and spread gradually (‘Jacksonian epilepsy’). Prolonged episodes may leave paresis of the involved limb lasting for several hours (Todd’s palsy).


Partial sensory seizures: Seizures arising in the sensory cortex cause unpleasant tingling or ‘electric’ sensations in the contralateral face and limbs. A spreading pattern like a Jacksonian seizure may occur, but is much faster (in seconds) than the ‘march’ of a migrainous focal sensory attack (10–15 mins).




EPILEPSY


Epilepsy is a tendency to have seizures and is a symptom of brain disease rather than a disease itself. A single seizure is not epilepsy but is an indication for investigation. The recurrence rate after a first seizure approaches 70% during the first year. The lifetime risk of having a single seizure is ∼5%, whilst the prevalence of epilepsy is ∼0.5%.





Management






Immediate care of seizures: Little can or need be done for a person whilst a major seizure is occurring except first aid and common-sense manoeuvres (Box 16.2).



Restrictions: Patients should be made aware of the riskiness of activities where loss of awareness would be dangerous, until good control of seizures has been established. This includes work or recreational activities involving exposure to heights, dangerous machinery, open fires or water. In the UK and many other countries, legal restrictions regarding vehicle driving apply to patients with epilepsy.


Anticonvulsant drug therapy (see also p. 781): Drug treatment should be considered after more than one seizure has occurred. Of patients whose epilepsy is controllable, only a single drug is necessary in 80%. Dose regimens should be kept as simple as possible to promote compliance. The first line of treatment should be one of the established drugs (Box 16.3), with more recently introduced drugs as second choice. Try up to three agents singly before resorting to combinations; beware drug interactions. Phenytoin and carbamazepine induce liver enzymes and therefore are not ideal for women wishing to use oral contraception. Occasional phenytoin and carbamazepine blood levels can be checked to confirm appropriate dose and to check compliance. There is no relationship between drug levels of sodium valproate and anticonvulsant efficacy.





STATUS EPILEPTICUS


Status epilepticus exists when a series of seizures occurs over 30 mins without the patient regaining awareness between attacks. This usually refers to recurrent tonic clonic seizures and is a medical emergency. Status is never the presenting feature of idiopathic epilepsy but may be precipitated by abrupt withdrawal of anticonvulsant drugs, a major structural lesion or acute metabolic disturbance. Management is summarised in Box 16.4.






DISORDERS OF MOVEMENT


Lesions in various parts of the motor system produce distinctive patterns of motor deficit. These can be ‘negative’ symptoms (weakness, lack of coordination, lack of stability and stiffness) or ‘positive’ symptoms (tremor, dystonia, chorea, athetosis, hemiballismus, tics and myoclonus). When the lower limbs are affected, characteristic patterns of gait disorder may result.



THE MOTOR SYSTEM


A programme of movement formulated by the pre-motor cortex is converted into a series of muscle movements in the motor cortex and then transmitted to the spinal cord in the pyramidal tract (Fig. 16.2).



Lower motor neuron lesions: Loss of function of lower motor neurons causes loss of contraction in their units’ muscle fibres and the muscle will be weak and flaccid. Denervated muscle fibres atrophy, causing wasting. Re-innervation from neighbouring motor neurons occurs but the neuromuscular junctions are unstable, causing fasciculations (visible to the naked eye because the motor units are larger than normal).


Upper motor neuron (pyramidal) lesions: When the spinal cord is disconnected from the higher motor hierarchies, the anterior horn motor neurons are under the uninhibited influence of the spinal reflex mechanisms. An upper motor neuron lesion therefore manifests clinically with brisk tendon stretch reflexes, ‘spastic’ increase in tone, and extensor plantar responses. Spasticity takes time to develop and may not be present for weeks.


Extrapyramidal lesions: There is an increase in tone, which is continuous throughout the range of movement at any speed of stretch (‘lead-pipe’ rigidity). Involuntary movements are present, and a tremor combined with rigidity produces typical ‘cogwheel’ rigidity. Rapid movements are slowed (bradykinesia). Extrapyramidal lesions also cause postural instability, precipitating falls.


Cerebellar lesions: These cause lack of coordination on the same side of the body. The initial movement is normal but accuracy deteriorates as the target is approached, producing an ‘intention tremor’. The distances of targets are misjudged (dysmetria), resulting in ‘past-pointing’. The ability to produce rapid, regularly alternating movements is impaired (dysdiadochokinesis). Disorders of the central vermis of the cerebellum produce a characteristic ataxic gait.



A DIAGNOSTIC APPROACH TO LIMB WEAKNESS (Box 16.5, Fig. 16.3)















GAIT DISORDERS


Patterns of weakness, loss of coordination and proprioceptive sensory loss produce a range of abnormal gaits. Neurogenic disorders need to be distinguished from skeletal abnormalities, usually characterised by pain producing an antalgic gait, or limp.


Pyramidal gait: Upper motor neuron (pyramidal) lesions cause a gait in which the upper limb is held in flexion and the lower limb is kept relatively extended. In a hemiplegia, the asymmetry between the affected and normal sides is obvious. In a paraparesis, both lower limbs move slowly, swung from the hips and dragged on the ground in extension.


Foot drop: Weakness of ankle dorsiflexion disrupts the normal gait cycle. Descent of the foot is less controlled, making a slapping noise, and the foot may be lifted higher, producing a high-stepping gait.


Waddling gait of proximal muscle weakness: In proximal muscle weakness, usually caused by muscle disease, the hips are not properly fixed and trunk movements are exaggerated, producing a rolling or waddling gait.


Cerebellar ataxia: Patients with lesions of the central parts of the cerebellum (the vermis) walk with a characteristic broad-based gait, ‘like a drunken sailor’.


Gait apraxia: There is normal power in the legs and no abnormal cerebellar signs or proprioception loss, yet the patient cannot formulate the motor act of walking. This higher cerebral dysfunction occurs in bilateral hemisphere disease, such as normal pressure hydrocephalus and diffuse frontal lobe disease.


Sensory ataxia: Loss of joint position sense makes walking unreliable. The feet tend to be placed on the ground with greater emphasis, resulting in a ‘stamping’ gait.


Extrapyramidal gait: Patients have difficulty initiating walking and controlling the pace of their gait. This produces the festinant gait: initial stuttering steps that quickly increase in frequency while decreasing in length.



INVOLUNTARY MOVEMENTS


Abnormal movements usually imply a disorder in the basal ganglia, in which there is disinhibition of intrinsic rhythm generators or a disorder of postural control.


Rest tremor: A tremor is a rhythmic oscillating movement of a limb or part of a limb, or of the head. Rest tremor is pathognomonic of Parkinson’s disease. It is characteristically ‘pill-rolling’ and asymmetrical. Tremor of the head in the upright position (‘titubation’) is not a rest tremor since this is a postural tremor, disappearing when the head is supported.


Action tremor: More common than rest tremor. The potential causes are numerous:









Chorea: Jerky, small-amplitude, purposeless involuntary movements. There are numerous potential causes:







Ballism: More dramatic than chorea, ballistic movements of the limbs usually occur unilaterally (hemiballismus) in vascular lesions of the subthalamic nucleus.


Athetosis: Slower writhing movements of the limbs. These are often combined with chorea and are then termed ‘choreo-athetoid’ movements.


Dystonia: A movement disorder in which a limb (or the head) involuntarily takes up an abnormal posture. This may be generalised in basal ganglia disease, or may be focal or segmental, as in spasmodic torticollis when the head involuntarily turns to one side. Other segmental dystonias may cause abnormal disabling postures during specific actions (e.g. writer’s cramp) and can be treated with botulinum toxin to the responsible muscles.


Myoclonus: Brief, isolated, random, non-purposeful jerks of muscle groups in the limbs. They occur normally at the onset of sleep (hypnic jerks). Myoclonus can occur in epilepsy, from subcortical structures or from diseased segments of the spinal cord.


Tics: Repetitive semi-purposeful movements such as blinking, winking, grinning or screwing up of the eyes. Unlike with other involuntary movements, patients can suppress tics, at least for a short time.



SENSORY DISTURBANCE


Sensory symptoms are very common but do not always denote nervous system disorder. For example, tingling in the fingers of both hands and around the mouth commonly suggests hyperventilation. Damage to the afferent nervous pathways conveying touch and pain produces either the negative sensation of numbness, or positive symptoms such as paraesthesia and pain.




PATTERNS OF SENSORY DISTURBANCE (Fig. 16.4)









COMA AND BRAIN DEATH



COMA


Persistent loss of consciousness or coma indicates disorder of the arousal mechanisms in the brain stem and diencephalon. There are many causes of coma (Box 16.7). The history is crucial to establishing the cause and should be obtained from any witnesses. Neurological examination may reveal important findings, e.g. evidence of head injury, papilloedema, meningism or eye movement disorder.






ACUTE CONFUSIONAL STATE (DELIRIUM)


This is much more common than dementia. Unlike in dementia, there is a disturbance of arousal that accompanies the global impairment of mental function. There is drowsiness with disorientation, perceptual disturbances and muddled thinking. Patients typically fluctuate, confusion being worse at night, and there may be associated emotional disturbance or psychomotor changes. There are many possible causes (Box 16.9).





DISTURBANCE OF MEMORY


It is important to determine for how long the problem has existed, and exactly which aspects of memory are affected. Disturbance of episodic memory (‘short-term memory’) must be distinguished from semantic memory. The former can be selectively impaired in Korsakoff’s syndrome (often secondary to alcohol) or bilateral temporal lobe damage.






SPEECH AND LANGUAGE DISTURBANCE


Speech is the process whereby vocal sounds are used to convey meaning between individuals. A large volume of the cerebral cortex is involved in this complex process, mostly in the dominant hemisphere. The temporal speech comprehension region is referred to as Wernicke’s area. The language information then passes to Broca’s area. The motor commands generated here pass to the lips, tongue, palate, pharynx, larynx and respiratory muscles via the facial nerve and cranial nerves 9, 10 and 12, resulting in speech.









VISUAL DISTURBANCE



Apr 3, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Neurological disease

Full access? Get Clinical Tree

Get Clinical Tree app for offline access