The Polyneuropathies Specific Types


Incidence: 2 per 100 000 population per year. Characteristically it occurs 1-3 weeks after a viral or other infection or immunisation. Aetiology/pathology

The condition may follow viral infection, e.g. varicella-zoster, mumps and cytomegalovirus. It is also associated with Mycoplasma, Salmonella, Campylobacter infections, immunisations with both live and dead vaccines, antitoxins, trauma, surgery and, rarely, malignant disease and immunodeficiency.

Both antibody and cell-mediated reactions to peripheral nerve myelin are involved. Some patients produce antibodies to myelin glycoproteins or gangliosides others develop a T cell-mediated assault on myelin basic protein.

Segmental demyelination results with secondary axonal damage if the process is severe. Perivascular infiltration with lymphocytes occurs within peripheral nerves and nerve roots. Lymphocytes and macrophages release cytotoxic substances (cytokines) which damage Schwann cell/myelin. _____

Nerve cell

Blood vessel " *---Perivascular lymphocytic infiltrates

Nerve cell

COf oOtiQn

\ — If axon is damaged Myelin destruction Axon sparing

—Muscle shows denervation atrophy

When axon damage and nerve cell death occur, regeneration cannot take place. Clinical features

Sensory symptoms predominate at the beginning with paraesthesia of the feet, then hands. Pain, especially back pain, is an occasional initial symptom. Weakness next develops - this may be generalised, proximal in distribution or commence distally and ascend. In severe cases, respiratory and bulbar involvement occurs. Weakness is maximal three weeks after the onset. Tracheostomy/ventilation is required in 20% of cases. Facial weakness is present to some extent in 50% of cases. Papilledema may occur when CSF protein is markedly elevated (blocked arachnoid villi?). Autonomic involvement - tachycardia, fluctuating blood pressure, retention of urine - develops in some cases. Sensory signs are uncommon. Investigations

CSF protein is elevated in most patients but often not-until the second or third week of illness. Cells are usually absent but in 20% up to 50 cells/mm3 may be found. Nerve conduction studies

When carried out early in the illness, these may be normal. Findings of multifocal demyelination soon develops with slowing of motor conduction, conduction block and prolonged distal motor latencies. Ancillary investigations

Performed to identify any precipitating infection: e.g. viral studies. Electrolytes are checked for inappropriate secretion of antidiuretic hormone and immune complex glomerulonephritis.

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