PERIPHERAL NERVE DISEASE

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  • All are myelinated except C fibres that carry impulses from pain receptors.
  • Mechanisms of damage to peripheral nerves
    • myelin sheath is produced by Schwann cells
    • Blood supply is via vasa nervorum.
    • Demyelination
      • Is seen in Guillain–Barré syndrome, post-diphtheritic neuropathy and many hereditary sensorimotor neuropathies.
    • Axonal degeneration
      • Axon damage leads to the nerve fibre dying back from the periphery. Conduction velocity initially remains normal (cf. demyelination) because axonal continuity is maintained in surviving fibres.
      • Axonal degeneration occurs typically in toxic neuropathies.
    • Wallerian degeneration
      • This describes changes following nerve section.
      • Both axon and distal myelin sheath degenerate, over several weeks.
  • Compression
    • Focal demyelination at the point of compression causes disruption of the myelin sheath.
    • This occurs typically in entrapment neuropathies, e.g. carpal tunnel syndrome
  • Infarction
    • Microinfarction of vasa nervorum occurs in diabetes and arteritis, e.g. polyarteritis nodosa, Churg–Strauss syndrome ,
    • Wallerian degeneration occurs distal to the ischaemic zone.
  • Infiltration
    • Infiltration of peripheral nerves by inflammatory cells occurs in leprosy and granulomas, e.g. sarcoid, and by neoplastic cells, causing neural metastases.
  • Axonal growth takes place at up to 1 mm/day.
  • Definitions
  • Polyneuropathy describes diffuse, symmetrical disease, usually commencing peripherally.
  • The course may be acute, chronic, static, progressive, relapsing or towards recovery.
  • Polyneuropathies are motor, sensory, sensorimotor and autonomic.
  • They are classified broadly into demyelinating and axonal types,
  • Widespread loss of tendon reflexes is typical, with distal weakness and distal sensory loss.
  • Radiculopathy means disease affecting nerve roots
  • Plexopathy, the brachial or lumbosacral plexus.
  • Myelopathy means disease of the cord.

 

MONONEUROPATHIES

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  • Carpal tunnel syndrome (CTS
    • median nerve entrapment at the wrist
    • CTS is typically not associated with any underlying disease.
    • CTS is, however, seen in:
      • hypothyroidism
      • diabetes mellitus
      • pregnancy (third trimester)
      • obesity
      • rheumatoid disease
      • acromegaly
      • amyloid
      • renal dialysis patients.
      • CTS also occurs following wrist trauma.
    • There is nocturnal tingling and pain in the hand and/or forearm, followed by weakness of thenar muscles.
    • Sensory loss in the palm and radial three-and-a-half fingers develops, followed by wasting of abductor pollicis brevis.
    • Tinel’s sign is often present
      • Tinel’s is elicited by tapping the flexor aspect of the wrist: this causes tingling and pain.
    • Phalen’s test positive
      • In Phalen’s, symptoms are reproduced on passive maximal wrist flexion.
    • A wrist splint at night or a local steroid injection in the wrist gives relief in mild cases.
    • In pregnancy CTS is often self-limiting as fluid retention subsides postpartum.
    • Reduction in obesity usually alleviates CTS.
    • Surgical decompression of the carpal tunnel is the definitive treatment.
  • Ulnar nerve compression
    • The nerve is compressed in the cubital tunnel at the elbow.
    • This follows prolonged or recurrent pressure and elbow fracture.
    • Weakness and wasting of ulnar innervated muscles leads to clawing of the handhypothenar muscles, interossei and medial two lumbricals
    • with sensory loss in the ulnar one- and-a-half fingers.
    • The deep, solely motor branch of the ulnar nerve can be damaged in the palm by repeated trauma, e.g. from a crutch, screwdriver handle, or cycle handlebars.
  • Radial nerve compression
    • The radial nerve is compressed acutely against the humerus, e.g. when the arm is draped over a hard chair for several hours, known as Saturday night palsy.
    • Wrist drop and weakness of brachioradialis and finger extension follow. Recovery is usual, though not invariable, within 1–3 months.
    • Posterior interosseous nerve compression in the forearm also leads to wrist drop, without weakness of brachioradialis.
  • Lateral cutaneous nerve of the thigh compression
    • This is also known as meralgia paraesthetica
  • Common peroneal nerve palsy
    • The common peroneal nerve (lateral popliteal nerve) is compressed against the head of the fibula following prolonged squatting, yoga, pressure from a cast, prolonged bed rest or coma, or for no apparent reason.
    • There is foot drop and weakness of ankle eversion.
    • The ankle jerk (S1) is preserved.
    • A patch of numbness develops on the anterolateral border of the dorsum of the foot and/or lower shin – the nerve has a small sensory twig.
  • Multifocal neuropathy (mononeuritis multiplex, multiple mononeuropathy)
  • This occurs in:
    • diabetes mellitus
    • leprosy
    • vasculitis
    • sarcoidosis
    • amyloidosis
    • malignancy
    • neurofibromatosis
    • HIV infection
  • Diagnosis is largely clinical, supported by electrical studies.
    • Several nerves become affected sequentially or simultaneously, e.g. ulnar, median, radial and lateral popliteal nerves.
    • When multifocal neuropathy is symmetrical, there is difficulty distinguishing it from polyneuropathy.
    • Where leprosy is prevalent, e.g. in India, a single nerve lesion can be the presenting feature.
  • Polyneuropathies
  • Chronic sensorimotor neuropathy: no cause found
  • progressive symmetrical numbness and tingling occurs in hands and feet, spreading proximally in a glove and stocking distribution.
  • Diphtheritic neuropathy
  • Palatal weakness followed by pupillary paralysis and a sensorimotor neuropathy occur several weeks after the throat infection
  • Cranial polyneuropathy
  • These can develop in diabetes, malignant infiltration, particularly with nasopharyngeal and breast carcinoma, lymphomas, sarcoidosis, as part of a paraneoplastic syndrome and occasionally with giant cell arteritis.

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  • Metabolic neuropathies
    • Diabetes mellitus.
      • Several varieties of neuropathy occur
        • symmetrical sensory polyneuropathy
        • acute painful neuropathy
        • mononeuropathy and multiple mononeuropathy:
        • cranial nerve lesions
        • isolated peripheral nerve lesions (e.g. carpal tunnel syndrome)
        • diabetic amyotrophy
        • autonomic neuropathy.
    • Uraemia.
      • Progressive sensorimotor neuropathy develops in chronic uraemia.
      • the neuropathy usually improves after transplantation.
    • Thyroid disease.
      • A mild chronic sensorimotor neuropathy is sometimes seen in both hyperthyroidism and hypothyroidism
      • Myopathy also occurs in hyperthyroidism
    • Porphyria.
      • In acute intermittent porphyria there are episodes of a severe, mainly proximal neuropathy in the limbs, sometimes with abdominal pain, confusion and coma.
      • Alcohol, barbiturates and intercurrent infection can precipitate attacks.
    • Amyloidosis – Polyneuropathy develops
    • Refsum’s disease or multifocal neuropathy
      • This is an autosomal recessive rarity.
      • It is a treatable sensorimotor polyneuropathy with ataxia, retinal damage and deafness
      • due to defective phytanic acid metabolism.
  • Toxic neuropathies
    • Alcohol
      • Polyneuropathy, mainly in the lower limbs, occurs with chronic alcohol abuse.
      • Calf pain is common.
      • Recurrence and progression occur with even small amounts of alcohol.
    • Drugs and industrial toxins
      • lead motor neuropathy
      • acrylamide (plastics industry), trichlorethylene, hexane, fat-soluble hydrocarbons, e.g. glue-sniffing,
      • arsenic and thallium polyneuropathy, initially sensory.
  • Vitamin deficiencies
    • Thiamin (vitamin B1)
      • Dietary deficiency causes beriberi
      • polyneuropathy and cardiac failure.
      • Alcohol is the commonest
      • Anorexia nervosa can cause
      • Wernicke–Korsakoff syndrome
        • thiamin-responsive encephalopathy
        • due to ischaemic damage in the brainstem and its connections.
        • It consists of:
        • eye signs nystagmus, bilateral lateral rectus palsies, conjugate gaze palsies, fixed pupils and, rarely, papilloedema
        • ataxia broad-based gait, cerebellar signs and vestibular paralysis with absent calorics
        • cognitive change amnestic syndrome with confabulation, restlessness, stupor and coma
        • delirium tremens
        • hypothermia and hypotension due to hypothalamic involvement
      • Erythrocyte transketolase activity is reduced but the test is rarely available.
  • Pyridoxine (vitamin B6)
    • Deficiency causes a mainly sensory neuropathy. In practical terms this is seen as limb numbness developing during anti- TB therapy in slow isoniazid acetylators
    • Prophylactic pyridoxine 10 mg daily is given with isoniazid.
  • Vitamin B12 (cobalamin)
    • Deficiency causes damage to the spinal cord, peripheral nerves and brain.
    • Subacute combined degeneration of the cord (SACD).
      • Combined cord and peripheral nerve damage is a sequel of Addisonian pernicious anaemia
      • Initially there is numbness and tingling of fingers and toes, distal sensory loss, particularly posterior column, absent ankle jerks and, with cord involvement, exaggerated knee jerks and extensor plantars.
      • Optic atrophy and retinal haemorrhage may occur.
      • In later stages sphincter disturbance, severe generalized weakness and dementia develop.
      • Exceptionally, dementia develops in the early stages.
      • Macrocytosis with megaloblastic marrow is usual though not invariable in SACD.
      • Parenteral B12 reverses nerve damage but has little effect on the cord and brain.
      • Without treatment, SACD is fatal within 5 years.
      • Copper deficiency is a very rare cause of a similar picture.
  • Charcot–Marie–Tooth disease
    • Charcot–Marie–Tooth (CMT) disease is also called peroneal muscular atrophy.
      • distal limb wasting and weakness that slowly progresses over many years, mostly in the legs, with variable loss of sensation and reflexes.
      • In advanced disease, distal wasting is so marked that the legs are said to resemble inverted champagne bottles.
      • Mild cases have pes cavus and toe clawing that can pass unnoticed.
      • HSMN Ia (CMT 1A) the commonest
      • autosomal dominant demyelinating neuropathy
      • caused by duplication (or point mutation) of a 1.5 megabase portion p11.2 of chromosome 17 encompassing the peripheral myelin protein 22 gene (PMP-22, 17p11.2).
    • HSMN III
      • HSMN III is a rare childhood demyelinating sensory neuropathy (Déjérine–Sottas disease) leading to severe incapacity during adolescence. Nerve roots become hypertrophied.
      • CSF protein is greatly elevated to 10 g/L or more
  • Neuropathy in cancer
    • Polyneuropathy is seen as a paraneoplastic syndrome (non- metastatic manifestation of malignancy), sometimes with anti-neuronal antibodies
    •  Polyneuropathy occurs in myeloma and other dysproteinaemic state
  • Neuropathies in systemic diseases
    • Vasculitic neuropathy occurs in SLE ,polyarteritis nodosa , Churg–Strauss syndrome ,rheumatoid disease ,sarcoidosis and giant cell arteritis
  • POEMS syndrome.
    • chronic inflammatory demyelinating Polyneuropathy
    • Organomegaly (hepatomegaly 50%),
    • Endocrinopathy (gynaecomastia and atrophic testes),
    • an M protein band
    • Skin hyperpigmentation.
  • Autonomic neuropathy
    • Autonomic neuropathy causes postural hypotension, urinary retention, erectile dysfunction, diarrhoea or occasionally constipation, diminished sweating, impaired pupillary responses and cardiac arrhythmias.
    • This can develop in diabetes and amyloidosis and may complicate Guillain–Barré syndrome.
  • HIV-associated polyneuropathies
    • Inflammatory demyelinating neuropathies similar to Guillain–Barré syndrome and CIDP are seen early in HIV infection, particularly during seroconversion.
    • The most common neuropathy seen later in HIV is a chronic distal neuropathy that is symmetrical and painful.
    • Severe lumbosacral polyradiculoneuropathy develops develops, with profound lower limb flaccid paralysis, areflexia and sphincter dysfunction.
    • All HIV-associated neuropathies respond poorly to retroviral therapy
  • Critical illness polyneuropathy
    • Some 50% of critically ill ITU patients with multiple organ failure and/or sepsis develop an axonal polyneuropathy.

Peripheral Neuropathy

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