DISEASES OF THE PERIPHERAL NERVES

Six principal mechanisms cause nerve malfunction: demyelination, axonal degeneration, e.g. due to a toxin, Wallerian degeneration following nerve section, compression, infarction (in arteritis) and infiltration by inflammatory cells, e.g. sarcoid.

Mononeuropathies

Mononeuropathy is a process affecting a single nerve, and multiple mono-neuropathy (or mononeuritis multiplex) is a process affecting several or multiple nerves. Mononeuropathy may be the result of acute compression, particularly where the nerves are exposed anatomically (e.g. the common peroneal nerve at the head of the fibula), or entrapment, where the nerve passes through a relatively tight anatomical passage (e.g. the carpal tunnel). It may also be caused by direct damage, e.g. major trauma, surgery or penetrating injuries.

Carpal tunnel syndrome

Carpal tunnel syndrome is the most common entrapment neuropathy. It results from pressure on the median nerve as it passes through the carpal tunnel.

Aetiology

It is usually idiopathic but may be associated with hypothyroidism, diabetes mellitus, pregnancy, obesity, rheumatoid arthritis and acromegaly.

Clinical features

The history is of pain and paraesthesiae in the hand, typically worse at night, when it may wake the patient. On examination there may be no physical signs; weakness and wasting of the thenar muscles and sensory loss of the palm and palmar aspects of the radial three and a half fingers. Tapping on the carpal tunnel may reproduce the pain (Tinnel’s sign).

Management

Treatment with nocturnal splints or local steroid injections gives temporary relief. Surgical decompression is the definitive treatment unless the condition is likely to resolve (e.g. with pregnancy, obesity).

Compression neuropathies may also affect the ulnar nerve (at the elbow), the radial nerve (caused by pressure against the humerus) and the common peroneal nerve (resulting from pressure at the head of the fibula).

Mononeuritis multiplex

Mononeuritis multiplex often indicates a systemic disorder (Table 17.19); treatment is that of the underlying disease. Acute presentation is most com-monly due to vasculitis when prompt treatment with steroids may prevent irreversible nerve damage.

Polyneuropathy

Polyneuropathy is an acute or chronic, diffuse, usually symmetrical, disease process and may involve motor, sensory and autonomic nerves, either alone or in combination. Sensory symptoms include numbness, tingling, ‘pins and needles’, pain in the extremities and unsteadiness on the feet. Numbness typically affects the distal arms and legs in a ‘glove and stocking’ distribution. Motor symptoms are usually those of weakness. Autonomic neuropathy causes postural hypotension, urinary retention, erectile

Table 17.22 Varieties of polyneuropathy
Guillain–Barré syndrome
Chronic inflammatory demyelinating polyradiculoneuropathy
Diptheritic polyneuropathy
Idiopathic sensorimotor neuropathy
Drugs: e.g. isoniazid, metronidazole, cisplatin, phenytoin
Toxins: alcohol, lead, arsenic, thallium
Metabolic: diabetes mellitus, uraemia, thyroid disease, porphyria, amyloidosis
Vitamin deficiency: B1 thiamin), B6 (pyridoxine), nicotinic acid, B12
Hereditary sensorimotor neuropathy
Neuropathy in cancer: paraneoplastic manifestation, myeloma
Autonomic neuropathy
HIV-associated neuropathy
Neuropathy in systemic disease: SLE, PAN, Churg–Strauss, RA, sarcoidosis, GCA
Critical illness neuropathy – ITU patients with multiorgan failure
SLE, systemic lupus erythematosus; PAN, polyarteritis nodosa; RA, rheumatoid arthritis;
GCA, giant cell arteritis

dysfunction, diarrhoea (or occasionally constipation), diminished sweating, impaired pupillary responses and cardiac arrhythmias. Many varieties of neuropathy affect autonomic function to some degree, but occasionally auto-nomic features predominate. This occurs in diabetes mellitus, amyloidosis and the Guillain-Barré syndrome.

A classification is given in Table 17.22. In Europe diabetes mellitus is the commonest cause. First-line investigations in a patient presenting with polyneuropathy include full blood count and erythrocyte sedimentation rate, serum vitamin B12, blood glucose, urea and electrolytes, liver biochemistry and sometimes nerve conduction studies (p. 738).

Guillain-Barré syndrome (GBS)

GBS is the most common acute neuropathy and is usually an inflammatory demyelinating, but occasionally axonal, polyneuropathy. It can lead to life-threatening respiratory failure.

Pathogenesis

GBS is usually triggered by an infection: Campylobacter jejuni, Epstein-Barr virus and cytomegalovirus have all been associated. It is thought that the infectious organism shares epitopes with an antigen in peripheral nerve tissue (ganglioside GM1 and GQ1b) leading to autoantibody mediated nerve cell damage formation.

Clinical features

There is progressive onset of limb weakness (usually symmetrical) that reaches its nadir within 4 weeks. Reflexes are lost early in the illness. There are often sensory symptoms, e.g. paraesthesias, but few sensory signs on examination. Disability ranges from mild to very severe, with involvement of the respiratory and facial muscles. Autonomic features, such as postural hypotension, cardiac arrhythmias, ileus and bladder atony, are sometimes seen. The Miller Fisher syndrome is a related variant that affects the cranial nerves to the eye muscles and is characterized by opthalmoplegia and ataxia.

Investigations

The diagnosis is established on clinical grounds and confirmed by nerve conduction studies showing slowing of motor conduction, prolonged distal motor latency and/or conduction block. CSF protein is non-specifically ele-vated, with a normal sugar and cell count. In the Miller Fisher syndrome antibodies against GQ1b have a sensitivity of 90%.

Differential diagnosis

Other causes of neuromuscular paralysis (hypokalaemia, polymyositis, botu-lism, poliomyelitis) can usually be excluded on clinical grounds and investiga-tion. MRI of the spine may be needed to exclude transverse myelitis or cord compression.

Management

Vital capacity is monitored 4-hourly to recognize respiratory muscle weakness. A fall below 80% of predicted or 20 mL/kg is an indication for transfer to ITU and possible mechanical ventilation. There is ECG monitoring to document cardiac dysrhythmias associated with autonomic dysfunction.

Intravenous immunoglobulin (0.4g/kg body weight daily for 5 consecutive days) is the standard treatment. It reduces duration and severity of paralysis and has fewer side-effects that plasma exchange. Immunoglobulin is contra-indicated in patients with IgA deficiency (measure serum levels before treatment) in whom it causes severe allergic reactions. Supportive treatment includes heparin to prevent thrombosis, physiotherapy to prevent contrac-tures and nasogastric or PEG feeding for patients with swallowing problems. Visiting and counselling services are offered by past patients through the Guillain-Barré Syndrome Support Group (http://www.gbs.org.uk).

Recovery begins between several days and 6 weeks from the outset. Prolonged ventilation may be necessary. Improvement towards independent mobility is gradual over many months but may be incomplete. About 10% of patients die (respiratory failure, pulomomary emboli, or infection) and 20% have permanent neurological damage.

Vitamin deficiency neuropathies

Thiamin (vitamin B1)

Thiamin deficiency occurs in chronic alcohol-dependent patients (where little food is consumed), in starvation from any cause, and in beriberi (poorest areas of South East Asia where only polished rice is consumed). Presentation is with the Wernicke-Korsakoff syndrome (p. 604), polyneuropathy and cardiac failure (rarely seen in Western countries). Treatment is with thiamin (250 mg daily i.m. or i.v.) for 3 days. Anaphylaxis can occur with parenteral thiamin. Thiamin must always be given before intravenous glucose in these high-risk patients.

Pyridoxine (vitamin E6)

Deficiency causes mainly a sensory neuropathy. It may be precipitated during isoniazid therapy (which complexes with pyridoxal phosphate) for tubercu-losis in those who acetylate the drug slowly. Prophylactic pyridoxine (10 mg daily) is given with isoniazid.

Vitamin B12

Deficiency causes a polyneuropathy and the syndrome of subacute combined degeneration of the cord. This comprises distal sensory loss (particularly the posterior column), absent ankle jerks (as a result of the neuropathy) and evidence of cord disease (exaggerated knee jerk reflexes, extensor plantar responses). Treatment is with intramuscular vitamin B12 (p. 241), which reverses the peripheral nerve damage but has little effect on the CNS (cord and brain signs).

Hereditary sensorimotor neuropathy

This is a large and complex group with variable genetic mutations. Charcot-Marie-Tooth disease, also called peroneal muscular atrophy, is the common-est with autosomal dominant inheritance in most cases. There is distal limb wasting and weakness that progress over many years, mostly in the legs, with variable loss of sensation and reflexes. In advanced cases the distal wasting below the knees is so marked that the legs resemble ‘inverted champagne bottles'.

Ebook Essentials of Kumar and Clark's Clinical Medicine, 5e

1. Ethics and communication

Ethics and communication

2. Infectious diseases

Infectious diseases

3. Gastroenterology and nutrition

Gastroenterology and nutrition

4. Liver, biliary tract and pancreatic disease

Liver, biliary tract and pancreatic disease
LIVER BIOCHEMISTRY AND LIVER FUNCTION TESTS
SYMPTOMS AND SIGNS OF LIVER DISEASE
JAUNDICE
HEPATITIS
NON - ALCOHOLIC FATTY LIVER DISEASE (NAFLD)
CIRRHOSIS
COMPLICATIONS AND EFFECTS OF CIRRHOSIS
LIVER TRANSPLANTATION
TYPES OF CHRONIC LIVER DISEASE AND CIRRHOSIS
PRIMARY SCLEROSING CHOLANGITIS
BUDD - CHIARI SYNDROME
LIVER ABSCESS
LIVER DISEASE IN PREGNANCY
LIVER TUMOURS
GALLSTONES
THE PANCREAS
CARCINOMA OF THE PANCREAS
NEUROENDOCRINE TUMOURS OF THE PANCREAS

5. Haematological disease

Haematological disease
ANAEMIA
Assessment and treatment of suspected neutropenic sepsis
HAEMOLYTIC ANAEMIA
INHERITED HAEMOLYTIC ANAEMIAS
ACQUIRED HAEMOLYTIC ANAEMIA
MYELOPROLIFERATIVE DISORDERS
THE SPLEEN
BLOOD TRANSFUSION
THE WHITE CELL
HAEMOSTASIS AND THROMBOSIS
THROMBOSIS
THERAPEUTICS

6. Malignant disease

Malignant disease
MYELOABLATIVE THERAPY AND HAEMOPOIETIC STEM CELL TRANSPLANTATION
THE LYMPHOMAS
THE PARAPROTEINAEMIAS
PALLIATIVE MEDICINE AND SYMPTOM CONTROL

7. Rheumatology

Rheumatology
COMMON INVESTIGATIONS IN MUSCULOSKELETAL DISEASE
COMMON REGIONAL MUSCULOSKELETAL PROBLEMS
BACK PAIN
OSTEOARTHRITIS
INFLAMMATORY ARTHRITIS
THE SERONEGATIVE SPONDYLOARTHROPATHIES
Clinical features, Investigations
INFECTION OF JOINTS AND BONES
AUTOIMMUNE RHEUMATIC DISEASES
SYSTEMIC INFLAMMATORY VASCULITIS
DISEASES OF BONE
THERAPEUTICS

8. Water, electrolytes and acid–base balance

WATER AND ELECTROLYTE REQUIREMENTS
BODY FLUID COMPARTMENTS
REGULATION OF BODY FLUID HOMEOSTASIS
PLASMA OSMOLALITY AND DISORDERS OF SODIUM REGULATION
DISORDERS OF POTASSIUM REGULATION
DISORDERS OF MAGNESIUM REGULATION
DISORDERS OF ACID - BASE BALANCE
THERAPEUTICS

9. Renal disease

Renal disease
INVESTIGATION OF RENAL DISEASE
GLOMERULAR DISEASES
NEPHROTIC SYNDROME
URINARY TRACT INFECTION
TUBULOINTERSTITIAL NEPHRITIS
HYPERTENSION AND THE KIDNEY
RENAL CALCULI AND NEPHROCALCINOSIS
URINARY TRACT OBSTRUCTION
ACUTE RENAL FAILURE/ACUTE KIDNEY INJURY
CHRONIC KIDNEY DISEASE
RENAL REPLACEMENT THERAPY
CYSTIC RENAL DISEASE
TUMOURS OF THE KIDNEY AND GENITOURINARY TRACT
DISEASES OF THE PROSTATE GLAND
TESTICULAR TUMOUR
URINARY INCONTINENCE

10. Cardiovascular disease

COMMON PRESENTING SYMPTOMS OF HEART DISEASE
INVESTIGATIONS IN CARDIAC DISEASE
CARDIAC ARRHYTHMIAS
HEART FAILURE
ISCHAEMIC HEART DISEASE
RHEUMATIC FEVER
VALVULAR HEART DISEASE
PULMONARY HEART DISEASE
MYOCARDIAL DISEASE
CARDIOMYOPATHY
PERICARDIAL DISEASE
SYSTEMIC HYPERTENSION
ARTERIAL AND VENOUS DISEASE
ELECTRICAL CARDIOVERSION
DRUGS FOR ARRHYTHMIAS
DRUGS FOR HEART FAILURE
DRUGS AFFECTING THE RENIN - ANGIOTENSIN SYSTEM
NITRATES, CALCIUM - CHANNEL BLOCKERS AND POTASSIUM - CHANNEL ACTIVATORS

11. Respiratory disease


Respiratory disease
TUBERCULOSISnd
DIFFUSE DISEASES OF THE LUNG PARENCHYMA
OCCUPATIONAL LUNG DISEASE
CARCINOMA OF THE LUNG
DISEASES OF THE CHEST WALL AND PLEURA
DISORDERS OF THE DIAPHRAGM

12. Intensive care medicine

Intensive care medicine

13. Drug therapy, poisoning, and alcohol misuse

Drug therapy, poisoning, and alcohol misuse

14. Endocrine disease

Endocrine disease
PITUITARY HYPERSECRETION SYNDROMES
THE THYROID AXIS
MALE REPRODUCTION AND SEX
FEMALE REPRODUCTION AND SEX
THE GLUCOCORTICOID AXIS
THE THIRST AXIS
DISORDERS OF CALCIUM METABOLISM
DISORDERS OF PHOSPHATE CONCENTRATION
ENDOCRINOLOGY OF BLOOD PRESSURE CONTROL
DISORDERS OF TEMPERATURE REGULATION
THERAPEUTICS

15. Diabetes mellitus and other disorders of metabolism

DIABETES MELLITUS
DIABETIC METABOLIC EMERGENCIES
COMPLICATIONS OF DIABETES
SPECIAL SITUATIONS
HYPOGLYCAEMIA IN THE NON - DIABETIC
DISORDERS OF LIPID METABOLISM
THE PORPHYRIAS

16. The special senses

THE EAR
THE NOSE AND NASAL CAVITY
THE THROAT
THE EYE

17. Neurology

COMMON NEUROLOGICAL SYMPTOMS
COORDINATION OF MOVEMENT
THE CRANIAL NERVES
COMMON INVESTIGATIONS IN NEUROLOGICAL DISEASE
UNCONSCIOUSNESS AND COMA
STROKE AND CEREBROVASCULAR DISEASE
EPILEPSY AND LOSS OF CONSCIOUSNESS
NERVOUS SYSTEM INFECTION AND INFLAMMATION
HYDROCEPHALUS
HEADACHE, MIGRAINE AND FACIAL PAIN
SPINAL CORD DISEASE
DEGENERATIVE NEURONAL DISEASES
DISEASES OF THE PERIPHERAL NERVES
MUSCLE DISEASES
MYOTONIAS
DELIRIUM
THERAPEUTICS

18. Dermatology

Dermatology

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