Neurological disease

Chapter 22 Neurological disease





The impact of neurological disease

Common symptoms and signs

Examination and formulation

Functional neuroanatomy

Cranial nerves

I: Olfactory nerve 

II: Optic nerve and visual system 

III, IV, VI: Oculomotor, trochlear and abducens nerves 

V: Trigeminal nerve 

VII: Facial nerve 

VIII: Vestibulo-cochlear nerve; cochlear nerve 

Lower cranial nerves IX, X, XI, XII 

Motor control systems

Corticospinal (pyramidal) system

Extrapyramidal system

Cerebellum

Tremor

Lower motor neurone (LMN) lesions

Spinal reflex arc

Sensory pathways and pain

Lesions of the sensory pathways 

Pain 

Bladder control and sexual dysfunction

Neurological tests

Neuro-imaging 

Unconsciousness and coma

The unconscious patient 

Stroke and cerebrovascular disease

Clinical syndromes 

Cortical venous thrombosis and dural venous sinus thrombosis 

Headache, migraine and facial pain

Primary headache disorders 

Secondary headache disorders 

Facial pain 

Epilepsy and loss of consciousness

Epilepsy 

Other causes of blackouts 

Sleep disorders 

Movement disorders

Parkinsonian disorders 

Other akinetic-rigid syndromes 

Hyperkinetic movement disorders 

Multiple sclerosis (MS)

Nervous system infection and inflammation

Meningitis 

Encephalitis 

Herpes zoster (shingles) 

Neurosyphilis 

Neurocysticercosis 

HIV and neurology 

Other infections 

Other inflammatory conditions 

Brain and spinal abscesses 

Brain tumours

Hydrocephalus

Traumatic brain injury

Spinal cord disease

Care of the patient with paraplegia 

Neurodegenerative diseases

Dementia 

Causes of dementia 

Motor neurone disease (MND) 

Congenital disorders

Cerebral palsy 

Dysraphism 

Neurogenetic disorders

Neurocutaneous syndromes 

Spinocerebellar ataxias (SCAs) 

Paraneoplastic syndromes

Peripheral nerve disease

Mononeuropathies 

Polyneuropathies (peripheral neuropathy) 

Plexus and nerve root lesions 

Muscle diseases

Inflammatory myopathies 

Metabolic and endocrine myopathies 

Neuromuscular junction disorders 

Muscular dystrophies 

Myotonias 

Channelopathies 

Stiff person syndrome 

Mitochondrial diseases 


The impact of neurological disease


Neurology is a large and diverse subject which covers many conditions that require long-term coordinated care and have serious effects on the daily lives of patients and their families. Neurology includes conditions as diverse as cognitive disorders involving higher level mental functioning through to disorders of peripheral nerve and skeletal muscle. It is a specialty requiring good clinical skills and examination technique which cannot be replaced with investigations or imaging techniques alone (Table 22.1).


Table 22.1 UK incidence of common neurological conditions










































Conditions Events per 100 000/year

Cerebrovascular events

210


Shingles (herpes zoster) and postherpetic neuralgia

150


Diabetic and other neuropathies

105


Epilepsy

46


Parkinson’s disease

19


Severe brain injury and subdural haematoma

13


All CNS tumours

9


Trigeminal neuralgia

8


Meningitis

7


Multiple sclerosis

7


Presenile dementia (below 65 years)

4


Myasthenia, all muscle and motor neurone disease

5



Common symptoms and signs


Pattern recognition in neurology – interpretation of history, symptoms and examination – is very reliable. Practical experience is vital. There are three critical questions in formulating a clinical diagnosis:



image What is/are the site(s) of the lesion(s)?


image What is the likely pathology?


image Does a recognizable disease fit this pattern?



FURTHER READING




Hirtz D, Thurman DJ, Gwinn-Hardy K et al. How common are the ‘common’ neurologic diseases? Neurology 2007; 68:326–337.


World Health Organization. The Global Burden of Disease. Geneva: WHO; 1996.




Difficulty walking and falls


Change in walking pattern is a common complaint (Box 22.1). Arthritis and muscle pain make walking painful and slow (antalgic gait). The pattern of gait is valuable diagnostically.



image Box 22.1


Common gait abnormalities




image Spasticity/hemiparesis


image Parkinson’s disease


image Cerebellar ataxia


image Position sense loss (stamping)


image Distal weakness (slapping)


image Proximal weakness (waddling)


image Apraxia of gait




Spasticity and hemiparesis

Spasticity (p. 1082), more pronounced in extensor muscles, with or without weakness, causes stiff and jerky walking. Toes of shoes become scuffed, catching level ground. Pace shortens; a narrow base is maintained. Clonus – involuntary extensor rhythmic leg jerking – may occur.


In a hemiparesis when spasticity is unilateral and weakness marked, the stiff, weak leg is circumducted and drags.



Parkinson’s disease: shuffling gait

There is muscular rigidity (p. 1118) throughout extensors and flexors. Power is preserved; the pace shortens, and slows to a shuffle; its base remains narrow. A stoop and diminished arm swinging become apparent. Gait becomes festinant (hurried) with short rapid steps. There is difficulty turning quickly and initiating movement, sometimes with falls. Retropulsion means small backward steps, taken involuntarily when a patient is halted.



Cerebellar ataxia: broad-based gait

In lateral cerebellar lobe disease (p. 1083) stance becomes broad-based, unstable and tremulous. Ataxia describes this incoordination. When walking, the person tends to veer to the side of the affected cerebellar lobe.


In disease of midline structures (cerebellar vermis), the trunk becomes unsteady without limb ataxia, with a tendency to fall backwards or sideways – truncal ataxia.



Sensory ataxia: stamping gait

Peripheral sensory lesions (e.g. polyneuropathy, p. 1145) cause ataxia because of loss of proprioception (position sense). Broad-based, high-stepping, stamping gait develops. This form of ataxia is exacerbated by removal of sensory input (e.g. vision) and worse in the dark. Romberg’s test, first described in sensory ataxia of tabes dorsalis (p. 1129), becomes positive.



Lower limb weakness: slapping and waddling gaits

When weakness is distal, each foot must be lifted over obstacles. When ankle dorsiflexors are weak, e.g. in a common peroneal nerve palsy (p. 1144), the sole returns to the ground with an audible slap.


Weakness of proximal lower limb muscles (e.g. polymyositis, muscular dystrophy) causes difficulty rising from sitting. Walking becomes a waddle, the pelvis being poorly supported by each leg.



Gait apraxia

With frontal lobe disease (e.g. tumour, hydrocephalus, infarction), acquired walking skills become disorganized. Leg movement is normal when sitting or lying but initiation and organization of walking fail. Shuffling small steps (marche à petits pas), gait ignition failure or undue hesitancy may predominate. Urinary incontinence and dementia are often present.



Falls

Falls in the elderly are a major cause of hospital admission, e.g. following fractures. Often no precise cause can be found. A multidisciplinary approach is essential, e.g. reviewing risk factors such as rugs, stairs, footwear and home circumstances.



FURTHER READING




Dykes PC, Carroll DL, Hurley A et al. 2010 Fall prevention in acute care hospitals. JAMA 304(17):1912–1918.



Dizziness, vertigo and blackouts


Dizziness covers many complaints, from a vague feeling of unsteadiness to severe, acute vertigo. It is frequently used to describe light-headedness, panic, anxiety, palpitations and chronic ill-health. The real nature of this symptom must be determined.


Vertigo (p. 1078) means the illusion of movement, a sensation of rotation or tipping. The patient feels the surroundings are spinning or moving. This is distressing and often accompanied by nausea or vomiting.


Blackout, like dizziness, is simply descriptive, implying either altered consciousness, visual disturbance or falling. Epilepsy (p. 1112) and syncope are mentioned in detail (p. 1116); hypoglycaemia and anaemia must be considered. Commonly no sinister cause is found. A careful history is essential.


Collapse is a vague term, but often used. Avoid it.


No serious disease is found in many patients (>20%) referred with symptoms suggestive of possible neurological conditions.


Fatigue is common: when it is an isolated symptom, neurological disease is rarely discovered. There is a borderland (sometimes contentious) between neurology and psychiatry.



Examination and formulation


Following a short or detailed examination, relevant findings are summarized in a brief formulation – the basis for investigation, transfer of information and management (Practical Boxes 22.1, 22.2 and Table 22.2).



image Practical Box 22.1


Five-part short neurological examination




1.


image General demeanour

image Speech

image Gait

image Arm swinging

2.


image Fundi

image Pupils

image Eye movements

image Facial movements

image Tongue

3.


image Posture of outstretched arms

image Wasting, fasciculation

image Power, tone

image Coordination

image Reflexes

4.


image Power

image Tone

image Reflexes

image Plantar responses

5.


image Ask the patient


image Practical Box 22.2


10-part neurological examination




1. State of consciousness, arousal, appearance


2. Mental state, attitude, insight (see Box 22.5, p. 1069)


3. Cognitive function – orientation, recall, level of intellect, language, other cortical problems, e.g. apraxia


4. Gait and balance tests


5. Skull – contour, bruits


6. Neck – stiffness, palpation and auscultation of carotids


7. Cranial nerves (Table 22.3)


8. Motor system


Upper limbs:

image Wasting and fasciculation

image Posture of arms: drift, rebound, tremor

image Tone: spasticity, clonus, extrapyramidal rigidity

image Power: 0–5 scale (Table 22.2)

image Tendon reflexes: + or ++ normal; +++ pathological; 0 = absent with reinforcement

Thorax and abdomen:

image Respiration

image Thoracic and abdominal muscles

image Abdominal reflexes

image Cremasteric reflexes

Lower limbs:

image Wasting and fasciculation

image Tone, power and tendon reflexes

image Plantar responses

9. Coordination and fine movements


10. Sensory system



image First: is feeling in limbs, face and trunk normal?

Posterior columns:

image Vibration (128 Hz tuning fork)

image Joint position

image Light touch

image 2-point discrimination (normal: 0.5 cm finger tips, 2 cm soles)

Spinothalamic tracts:

image Pain: use a split orange-stick or a sterile pin

image Temperature: warm and cold objects

If sensation is abnormal, chart areas involved

Table 22.2 Six grades of muscle power
























Grade Definition

5

Normal power


4

Active movement against gravity and resistance


3

Active movement against gravity


2

Active movement with gravity eliminated


1

Flicker of contraction


0

No contraction



FURTHER READING




Clarke C. The language of neurology – symptoms, signs and basic investigations. In: Clarke C, Howard R, Rossor M et al. (eds) Neurology: A Queen Square Textbook. Oxford: Blackwell; 2009.



Functional neuroanatomy




The neurone and synapse


The neurone is the functional unit of the entire nervous system (Fig. 22.1). Its cell body and axon terminate in a synapse. Size and type of each group of neurones vary. A thoracic spinal cord α-motor neurone has an axonal length of >1 metre and innervates between several hundred and 2000 muscle fibres in one leg – a motor unit. By contrast, some spinal or intracerebral interneurones have axons under 100 µm long, terminating on one neuronal cell body.


image

Figure 22.1 The functional unit: neurone and neurotransmitters. (a) The action potential, i.e. nerve impulse, travels down the axon. Microtubules carry neurotransmitters to nerve endings. (b) Action potential I depolarizes the synaptic membrane, opening voltage-gated calcium channels. (c) Influx of calcium ions cause vesicles to fuse with the membrane allowing neurotransmitter binding to receptors (i) and activation of secondary messengers that modulate gene transcription and also open ligand-gated channels (ii). This allows ions to enter, depolarize the membrane and initiate action potential II.



Neurotransmitters


Neurotransmitters are excitatory (acetylcholine, noradrenaline, adrenaline, 5-hydroxytryptamine, dopamine, glutamate and aspartate) or inhibitory (γ-aminobutyric acid (GABA), histamine and glycine). Neuropeptides, e.g. vasopressin, ACTH, substance P and opioid peptides, as well as the purines (ATP and AMP) are both excitatory and inhibitory.


Synaptic transmission is mediated by neurotransmitters released by action potentials passing down an axon. Neurotransmitters activate postsynaptic receptors and are removed by transporter proteins. The neurotransmitter-receptor reaction increases ionic permeability and propagates a further action potential. Axonal electrical activity and synaptic chemical release is the basis of neurological function.



Clinical features of focal brain lesions: general mechanisms


The symptoms and signs suggest the area of the brain that is malfunctioning (e.g. aphasia – the left frontal lobe, hemiparesis – internal capsule or a Bell’s palsy – Vllth cranial (facial) nerve).


Focal lesions of the cortex, and lesions throughout the nervous system, cause symptoms and signs by two processes:



image Suppression or destruction of neurones and surrounding structures (Fig. 22.2). This is the commonest process – part of the system simply fails to work.


image Synchronous discharge of neurones by irritative lesions (Fig. 22.3), e.g. cortical lesions, causes epilepsy, either partial or generalized.


image

Figure 22.2 Principal features of destructive cortical lesions in a right-handed individual.


image

Figure 22.3 Effects of irritative cortical lesions.



Localization within the cerebral cortex


This subject causes unnecessary difficulty. Work on neuronal networks, functional imaging and plasticity questions the traditional views of highly specific localization of cortical function. The following paragraphs summarize areas of clinical relevance.




The dominant hemisphere (usually left)

The concept of cerebral dominance arose from a simple observation: right-handed stroke patients with acquired language disorders had destructive lesions within the left hemisphere. Right-handed (and 70% of left-handed) people have language function on the left.


More specifically, destructive lesions within the left fronto-temporo-parietal region cause disorders of communication:



image Spoken language – aphasia, also called dysphasia


image Writing – agraphia


image Reading – acquired alexia.


Developmental dyslexia describes delayed, disorganized reading and writing ability in children, usually with normal intelligence.



Aphasia

Aphasia is loss of or defective language from damage to the speech centres within the left hemisphere. Numerous varieties have been described.



Broca’s (expressive, anterior) aphasia

Damage in the left frontal lobe causes reduced speech fluency with relatively preserved comprehension. The patient makes great efforts to initiate language, which becomes reduced to a few disjointed words with failure to construct sentences. Patients who recover say they knew what they wanted to say, but could not get the words out.



Wernicke’s (receptive, posterior) aphasia

Left temporo-parietal damage leaves fluency of language but words are muddled. This varies from insertion of a few incorrect or non-existent words into speech to a profuse outpouring of jargon (i.e. rubbish with wholly non-existent words). Severe jargon aphasia is bizarre and often mistaken for psychotic behaviour.


Patients who recover from Wernicke’s aphasia say that they found speech, both their own and others’, like an unintelligible foreign language, i.e. incomprehensible, but they could neither stop speaking nor understand speech.



Nominal (anomic, amnestic) aphasia

This means difficulty naming familiar objects. Naming difficulty is an early feature in all types of aphasia.



Global (central) aphasia

This means the combination of the expressive problems of Broca’s aphasia and the loss of comprehension of Wernicke’s with loss of both language production and understanding. This is due to widespread damage to speech areas and is the commonest aphasia after a severe left hemisphere infarct. Writing and reading are also affected.



Dysarthria

Dysarthria is disordered articulation – slurred speech. Language is intact. Paralysis, slowing or incoordination of muscles of articulation or local discomfort causes various patterns of dysarthria. Examples are the gravelly speech of pseudobulbar palsy (p. 1080), the jerky, ataxic speech of cerebellar lesions, the monotone of Parkinson’s, and speech in myasthenia that fatigues and dies away. Many aphasic patients are also dysarthric.



The non-dominant hemisphere

Disorders in right-handed patients with right hemisphere lesions are often difficult to recognize. There are abnormalities of perception of internal and external space. Examples are losing the way in familiar surroundings, failing to put on clothing correctly (dressing apraxia), or failure to draw simple shapes – constructional apraxia.



Memory and its disorders

Disorders of memory follow damage to the medial surfaces of both temporal lobes and their brainstem connections – the hippocampi, fornices and mammillary bodies. Bilateral lesions are necessary to cause amnesia. In all organic memory disorders recent events are recalled poorly, in contrast to the relative preservation of distant memories.


Memory loss (the amnestic syndrome) is part of dementia (p. 1137) but also occurs as an isolated entity (Box 22.2).



image Box 22.2


Causes of an amnestic syndrome




image Dementia


image Alcohol (Wernicke–Korsakoff syndrome)


image Head injury (severe)


image Anoxic brain damage and following carbon monoxide poisoning


image Posterior cerebral artery occlusion (bilateral)


image Herpes simplex encephalitis


image Chronic sedative and solvent abuse


image Bilateral invasive tumours


image Following hypoglycaemia


image Arsenic poisoning (very rare)



Neuroanatomy: essential elements


For clinical purposes the complexity of neuroanatomy must be reduced to its core elements:



image Cranial nerves


image Three systems of motor control:


– corticospinal or pyramidal system

– extrapyramidal system

– cerebellum

image Motor unit


image Reflex arc


image Sensory pathways and pain


image Control of the bladder and sexual function.



Cranial nerves (Table 22.3)



I: Olfactory nerve


This sensory nerve arises from olfactory (smell) receptors within nasal mucosa. Branches pierce the cribriform plate and synapse in the olfactory bulb. The olfactory tract passes to the olfactory cortex.


Table 22.3 Cranial nerves



























































Number Name Main clinical action

I

Olfactory

Smell


II

Optic

Vision, fields, afferent light reflex


III

Oculomotor

Eyelid elevation, eye elevation, ADduction, depression in ABduction, efferent (pupil)


IV

Trochlear

Eye intorsion, depression in ADduction


V

Trigeminal

Facial (and corneal) sensation, mastication muscles


VI

Abducens

Eye ABduction


VII

Facial

Facial movement, taste fibres


VIII

Vestibular
Cochlear

Balance and hearing


 

Cochlear

 


IX

Glossopharyngeal

Sensation – soft palate, taste fibres


X

Vagus

Cough, palatal and vocal cord movements


XI

Accessory

Head turning, shoulder shrugging


XII

Hypoglossal

Tongue movement


Anosmia (loss of sense of smell) is caused by head injury (shearing of olfactory neurones as they pass through the cribriform plate at the skull base) or tumours of the olfactory groove (e.g. meningioma). Olfaction is temporarily (occasionally permanently) lost or diminished after upper respiratory infections and with local disorders of the nose. Many patients with gradual onset anosmia over many years may be unaware of the deficit, e.g. in Parkinson’s disease where anosmia precedes motor symptoms by many years but is often not noticed by the patient.


Detailed smell testing is difficult in routine clinical practice and rarely performed. Adequate testing requires use of commercially available kits such as scratch and sniff cards or odour filled pens with forced multiple choice identification.



II: Optic nerve and visual system (Fig. 22.4)


Light regulated by the pupillary aperture is converted into action potentials by retinal rod, cone and ganglion cells (see page 1055). The lens, under control of the ciliary muscle, produces the image (inverted) on the retina. Axons in the optic nerve (1) decussate at the optic chiasm (2), fibres from the nasal retina cross and join with uncrossed fibres originating in the temporal retina to form the optic tract (3). Each optic tract thus carries information from the contralateral visual hemifield.


image

Figure 22.4 The visual pathway. 1. Mononuclear field loss – complete optic nerve lesion. 2. Bitemporal hemianopia – chiasmal lesion. 3. Homonymous hemianopia – optic tract lesion. 4. Homonymous quadrantanopia – temporal lesion. 5. Homonymous quadrantanopia – parietal lesion. 6. Homonymous hemianopia with macular sparing – occipital cortex or optic radiation. 7. Homonymous hemianopia (hemiscotoma) – occipital pole lesion.


From the lateral geniculate body, fibres pass in the optic radiation through the parietal and temporal lobes (4 and 5) to reach the visual cortex of the occipital lobe (6 and 7), which is somatotopically organized with macular vision located at the occipital pole (see Fig. 22.4).


Beyond the visual cortex visual information is further processed by neighbouring visual association areas to detect lines, orientation, shapes, movement, colour and depth; there is even a distinct area responsible for face recognition.



Visual acuity


This is assessed in each eye with a Snellen chart and/or Near Vision Reading Types, corrected for refractive errors with lenses or a pinhole. The patient should stand 6 metres from a well-lit chart. Acuity is recorded as distance in metres from the chart over distance at which the line should be legible, e.g. 6/6 indicates ‘normal’ acuity and 6/60 very poor acuity.



Visual field defects


Visual fields are assessed at the bedside by confrontation – comparing the examiner’s and patient’s fields, one eye at a time and quadrant by quadrant. Patience and good technique are required to get reliable results. White and red targets (traditionally hatpins) are used to assess peripheral and central fields respectively although in practice a fingertip is often substituted as a cruder screening test. More detailed quantification of fields may be obtained using Goldmann (manual) or Humphrey (automated) perimetry testing.


Field defects are described as hemianopic when half the field is affected and quadrantanopic when a quadrant is affected. Lesions posterior to the optic chiasm produce homonymous field defects, indicating involvement of the same part of the visual field in both eyes as information from the two visual hemifields is separated beyond this point. Lesions damaging decussating nasal fibres at the optic chiasm cause bitemporal defects.




Retinal and local eye lesions

See page 1063 in Chapter 21.



Optic nerve lesions

Unilateral visual loss, commencing with a central or paracentral (off-centre) scotoma, is the hallmark of an optic nerve lesion. Because most fibres in the optic nerve subserve macular vision, lesions within the nerve disproportionately affect central vision and colour vision. A total optic nerve lesion causes unilateral blindness with loss of pupillary light reflex. Examination findings in optic neuropathy:



image Reduced acuity in affected eye


image Scotoma (usually central)


image Impaired colour vision (assess with Ishihara plates)


image An afferent pupillary defect (see below)


image Optic atrophy – pale disc (develops late)


Causes are listed in Box 22.3.



image Box 22.3


Causes of optic neuropathy




image Inflammatory (optic neuritis), e.g. demyelination, sarcoidosis, vasculitis


image Optic nerve trauma or compression, e.g. glioma, meningioma, aneurysm, bone disorders affecting orbit


image Toxic, e.g. tobacco-alcohol, ethambutol, methyl alcohol, quinine, hydroxy chloroquine, radiation


image Ischaemic optic neuropathy, e.g. giant cell arteritis


image Hereditary optic neuropathies, e.g. Leber’s


image Nutritional deficiency, e.g. vitamin B1 and B12


image Infection, e.g. orbital cellulitis, syphilis, TB


image Neurodegenerative disorders, e.g. leucodystrophies


image Papilloedema and its causes (Box 22.4)



Papilloedema

Papilloedema means swelling of the optic disc. Causes are shown in Box 22.4. The earliest signs of swelling are disc pinkness, with blurring and heaping up of disc margins, nasal first. There is loss of spontaneous pulsation of retinal veins within the disc. The physiological cup becomes obliterated, the disc engorged with dilated vessels. Small haemorrhages often surround the disc.



image Box 22.4


Causes of optic disc swelling




image Raised intracranial pressure (papilloedema)


image Brain tumour, abscess, or haemorrhage. Idiopathic intracranial hypertension, hydrocephalus


image Optic nerve disease


image Optic neuritis, e.g. multiple sclerosis


image Ischaemic optic neuropathy, e.g. giant cell arteritis


image Toxic optic neuropathy, e.g. methanol


image Venous occlusion


image Venous sinus thrombosis


image Central retinal vein thrombosis


image Orbital mass lesions


image Retinal vascular disease


image Malignant hypertension


image Vasculitis, e.g. systemic lupus erythematosus


image Metabolic causes


image Hypercapnia, chronic hypoxia, hypocalcaemia


image Disc infiltration


image Leukaemia, sarcoidosis, optic nerve glioma


Various conditions simulate true disc swelling. Marked hypermetropic (long-sighted) refractive errors make a disc appear pink, distant and ill-defined. Myelinated nerve fibres at disc margins and hyaline bodies (drusen, p. 1064) can be mistaken for disc swelling.


Disc infiltration also causes a swollen disc with raised margins (e.g. in leukaemia).


When there is doubt about disc oedema, i.v. fluorescein angiography is diagnostic; retinal leakage is seen with papilloedema.


Papilloedema produces few if any visual symptoms other than momentary visual obscurations with changes in posture. The underlying disease is the source of the patient’s symptoms. The blind spot is enlarged but this is not noticed by the patient. However, over time progressive and permanent constriction of visual fields occurs, ultimately culminating in optic atrophy.



Inflammatory optic neuropathy (optic neuritis)

Optic neuritis is one of the most common causes of subacute visual loss. Symptoms may vary from a mild fogging of central vision with colour desaturation to a dense central scotoma, but very rarely complete blindness. Pain on eye movements is almost universal. The optic disc usually appears normal despite severe visual loss (unless the inflammation is at the optic nerve head in which case the disc may appear swollen in the acute phase).


A plaque of demyelination within the optic nerve is the most common cause in Western populations. Dedicated MRI imaging of the optic nerves may show the inflammatory plaque and imaging of the brain may show additional inflammatory lesions which confer a higher risk of developing multiple sclerosis (MS). Approximately 50% of patients go on to develop MS with prolonged follow-up (see p. 1123). Recovery of visual acuity to 6/9 or better occurs in 95% of cases over months, with recovery time improved by high-dose i.v. steroids given acutely.


Optic neuritis may be caused by infective or other inflammatory disorders, e.g. sarcoidosis or vasculitides (see Box 22.3).



Anterior ischaemic optic neuropathy

The anterior part of the optic nerve is supplied by the posterior ciliary arteries, occlusion or hypoperfusion of which leads to infarction of all or part of the optic nerve head. There is sudden or stuttering altitudinal visual loss (typically the lower half of the visual field) with disc swelling, later replaced by optic atrophy. The other eye is later affected in one-third of cases.


Individuals with small hypermetropic discs seem to be predisposed, and often there are relatively few vascular risk factors. Less commonly arteritis is the cause (see p. 536).



Optic atrophy

Optic atrophy means disc pallor, from loss of axons, glial proliferation and decreased vascularity. This may eventually develop following any type of optic neuropathy of sufficient severity to extensively damage axons within the nerve, including chronic papilloedema.



Optic chiasm

Bitemporal hemianopia or quadrantanopia occurs with compression of the chiasm from above or below. Common causes are:



image Pituitary tumours (p. 946)


image Meningioma


image Craniopharyngioma.



Optic tract and optic radiation

Optic tract lesions (rare) cause a homonymous hemianopia (loss of the contralateral visual field in both eyes). Optic radiation lesions cause homonymous quadrantanopic defects. Temporal lobe lesions (e.g. tumour, infarction) cause upper quadrantic defects, and parietal lobe, lower.



Occipital cortex

Homonymous hemianopic defects are produced by unilateral posterior cerebral artery infarction (see p. 1101 stroke). The macular cortex (at each occipital pole) may be spared.


Widespread bilateral occipital lobe damage by infarction (‘top of the basilar’ syndrome), trauma or coning causes cortical blindness (Anton’s syndrome). The patient cannot see but characteristically lacks insight into this; he or she may even deny it. Pupillary responses remain normal (p. 1101).



The pupils


A slight difference between the size of each pupil (up to 1 mm) is common (physiological anisocoria) and does not vary with differing light levels. The pupil tends to become smaller and irregular in old age (senile miosis); anisocoria is more pronounced. Convergence becomes sluggish with ageing.


Pupillary reactions to light and accommodation may be tested (Fig. 22.5). A bright torch (not an ophthalmoscope light!) should be used to test the pupillary light reaction.


image

Figure 22.5 Pupillary light reflex. Afferent pathway: (1) Light activates optic nerve axons. (2) Axons (some decussating at the chiasm) pass through each lateral geniculate body, and (3) synapse at pretectal nuclei. Efferent pathway: (4) Action potentials pass to Edinger–Westphal nuclei of IIIrd nerve, then, (5) via parasympathetic neurones in IIIrd nerves to cause (6) pupil constriction.


Afferent pupillary defect. A complete optic nerve lesion causes a dilated pupil and an afferent pupillary defect (APD). For a left APD:



image The pupil is unreactive to light (i.e. the direct reflex is absent).


image The consensual reflex (constriction of the right pupil when the left is illuminated) is absent. Conversely, the left pupil constricts when light is shone in the intact right eye, i.e. the consensual reflex of the right eye remains intact.


Relative afferent pupillary defect (RAPD). This occurs with incomplete damage to one optic nerve relative to the other. An RAPD is a sensitive sign of optic nerve pathology and can provide evidence of an optic nerve lesion even after recovery of vision. For a left RAPD:



image Direct and indirect reflexes are intact in each eye but differ in relative strength.


image When the light is swung from one eye to the other, the left pupil dilates slightly when illuminated and constricts slightly when the right eye is illuminated (the consensual reflex is stronger than the direct).





Horner’s syndrome (see Box 22.5)

The sympathetic nervous supply to the eye is a three neurone pathway originating in the hypothalamus and descending by way of the brainstem and cervical cord to T1 nerve root, paravertebral sympathetic chain and, on via the carotid artery wall, to the eye. Damage to any part of the pathway results in Horner’s syndrome. This is significant not only because it affects vision but also because it may indicate a serious underlying pathology.



image Box 22.5


Causes of Horner’s syndrome



Hypothalamic, hemisphere and brainstem lesions




image Massive cerebral infarction


image Brainstem demyelination or lateral medullary infarction



Cervical cord




image Syringomyelia and cord tumours



T1 root




image Apical lung tumour or TB


image Cervical rib


image Brachial plexus trauma



Sympathetic chain and carotid artery in neck




image Following thyroid/laryngeal/carotid surgery


image Carotid artery dissection


image Neoplastic infiltration


image Cervical sympathectomy



Miscellaneous




image Congenital


image Cluster headache, usually transient


image Idiopathic


The clinical features of Horner’s syndrome are:



image Unilateral miosis (constricted pupil)


image Partial ptosis


image Loss of sweating on the same side (extent depending upon the level of the lesion)


image Subtle conjunctival injection and enophthalmos may be present


image The miosis is most easily seen in low light as the pupil cannot dilate, and may not be apparent in bright light.



Myotonic pupil (Holmes–Adie pupil)

This is a dilated, often irregular, pupil, more frequent in women; it is common and usually unilateral. There is no (or very slow) reaction to bright light and also incomplete constriction to convergence. This is due to denervation in the ciliary ganglion, of unknown cause, and has no other pathological significance. A myotonic pupil is sometimes associated with diminished or absent tendon reflexes.



Argyll Robertson pupil

Now rarely seen in clinical practice. A small, irregular pupil is fixed to light but constricts on convergence. The lesion is in the brainstem surrounding the aqueduct of Sylvius. Once considered diagnostic of neurosyphilis, it is now only occasionally seen in diabetes or MS.



III, IV, VI: Oculomotor, trochlear and abducens nerves


These cranial nerves supply the extraocular muscles and disorders commonly result in abnormal eye movements and diplopia (double vision) due to breakdown of conjugate (yoked) eye movements. Diplopia may also occur with local orbital lesions or myasthenia gravis.



Examining eye movements


Pursuit (slow) eye movements and saccadic eye movements are tested separately. The examiner assesses the range of eye movements in all directions and asks the patient to report double vision. Jerky pursuit movements with saccadic intrusion (i.e. brief fast saccades interspersed with slower pursuit movements), overshoot on saccadic movements and nystagmus may indicate cerebellar or brainstem pathology.



Control of eye movements


Fast voluntary eye movements originate in the frontal lobes. Fibres descend and cross in the pons to end in the centre for lateral gaze (paramedian pontine reticular formation – PPRF), close to the VIth nerve nucleus. Each PPRF also receives input from:



image the ipsilateral occipital cortex – pathway concerned with tracking objects


image the vestibular nuclei – pathways linking eye movements with position of the head and neck (vestibulo-ocular reflex, p. 1072).


Conjugate lateral eye movements are coordinated from each PPRF via the medial longitudinal fasciculus (MLF, Fig. 22.6). Fibres from the PPRF pass both to the ipsilateral VIth nerve nucleus (lateral rectus) and, having crossed the midline, to the opposite IIIrd nerve nucleus (medial rectus and other muscles) via the MLF, thus linking the eyes for lateral gaze.


image

Figure 22.6 PPRF and INO. Impulses from PPRF pass via ipsilateral VIth nerve nucleus to lateral rectus muscle (ABduction) and via medial longitudinal fasciculus to opposite IIIrd nerve nucleus and thus to opposite medial rectus muscle (ADduction). A lesion of the MLF (X) causes failure of or slow ADduction in the right eye and nystagmus in the left eye with left lateral gaze. PPRF, para-median pontine reticular formation; INO, internuclear ophthalmoplegia; MLF, medial longitudinal fasciculus.



Abnormalities of conjugate lateral gaze


A destructive lesion on one side allows the eyes to be driven by the intact opposite pathway. A left frontal destructive lesion (e.g. an infarct) leads to failure of conjugate lateral gaze to the right. In an acute lesion the eyes are often deviated to the side of the lesion, past the midline and therefore look towards the left (normal) limbs; there is usually a contralateral (i.e. right) hemiparesis.


In the brainstem a unilateral destructive lesion involving the PPRF leads to failure of conjugate lateral gaze towards that side. There is usually a contralateral hemiparesis and lateral gaze is deviated towards the side of the paralysed limbs.




Internuclear ophthalmoplegia (INO)

Damage to one MLF causes internuclear ophthalmoplegia (INO), a common complex brainstem eye movement disorder seen frequently in MS. In a right INO there is a lesion of the right MLF (Fig. 22.6). On attempted left lateral gaze the right eye fails to ADduct. The left eye develops nystagmus in ABduction. The side of the lesion is on the side of impaired ADduction, not on the side of the (obvious, unilateral) nystagmus. When present bilaterally, INO is almost pathognomonic of MS.



One and a half syndrome

Pontine infarction involving the PPRF, VIth nerve nucleus and MLF on one side results in an ipsilateral horizontal gaze palsy and an INO so that abduction of the opposite eye (with nystagmus) is the only horizontal eye movement possible. Vertical gaze and convergence are preserved as they have distinct neural control mechanisms.



Vestibulo-ocular (Doll’s eye) reflexes

Examination is of diagnostic value in coma (p. 898) and assessment of vertigo (p. 1079).



Abnormalities of vertical gaze


Failure of up-gaze may be caused by dorsal midbrain lesions, e.g. pinealoma or infarcts. When the pupillary light reflex fails in addition, this is called Parinaud’s syndrome. Defective up-gaze also develops in certain degenerative disorders (e.g. progressive supranuclear palsy). Some impairment of up-gaze occurs as part of normal ageing.



Nystagmus


Nystagmus is rhythmic oscillation of eye movement, and a sign of disease of the retina, cerebellum and/or vestibular systems and their connections. Nystagmus is either jerk or pendular. Nystagmus must be sustained within binocular gaze to be of diagnostic value – a few beats at the extremes of gaze are normal.





Jerk nystagmus

Jerk nystagmus (usual in neurological disease) is a fast/slow oscillation. This is seen in vestibular, VIIIth nerve, brainstem, cerebellar lesions. Direction of nystagmus is decided by the fast component, a reflex attempt to correct the slower, primary movement.



image Horizontal or rotary jerk nystagmus may be either of peripheral (vestibular) or central origin (VIIIth nerve, brainstem, cerebellum and connections).


– In peripheral lesions, nystagmus is usually acute and transient (minutes or hours) and associated with severe prostrating vertigo.

– In central lesions nystagmus tends to be long-lasting (weeks, months or more). Vertigo caused by central lesions tends to wane after days or weeks, the nystagmus outlasting it.

image Vertical jerk nystagmus is caused typically by central lesions.


image Down-beat jerk nystagmus is a rarity caused by lesions around the foramen magnum (e.g. meningioma, cerebellar ectopia).



Pendular nystagmus

Pendular describes movements to and fro, similar in velocity and amplitude. Pendular nystagmus is usually vertical and present in all directions of gaze. The causes are generally ocular (e.g. poor visual fixation from longstanding, severe visual impairment), or congenital.



III: Oculomotor nerve


The nucleus of the IIIrd nerve lies ventral to the aqueduct in the midbrain. It supplies four external ocular muscles (superior, inferior and medial recti, and inferior oblique), levator palpebrae superioris (which lifts the eyelid) and parasympathetic constriction of the pupil. Causes of a IIIrd nerve lesion are listed in Box 22.6.



image Box 22.6


Some causes of a IIIrd nerve lesion




image Aneurysm of the posterior communicating artery


image Infarction of IIIrd nerve, e.g. diabetes, atheroma


image Coning of the temporal lobe


image Midbrain infarction


image Midbrain tumour (primary or secondary)


Signs of a complete IIIrd nerve palsy:



image Unilateral complete ptosis (levator weakness)


image Eye deviated down and out (unopposed lateral rectus and superior oblique)


image A fixed and dilated pupil.


Patients do not complain of diplopia as the ptosis effectively covers the eye. Sparing of the pupil indicates parasympathetic fibres are undamaged; these run in a discrete bundle on the surface of the nerve, thus the pupil is of normal size and reacts normally. Diabetic IIIrd nerve infarction is usually painless and pupil sparing, unlike compression by a posterior communicating artery aneurysm.

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Apr 1, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Neurological disease

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