Disease

NEUROPATHY (see page 427)

Sensory neuropathy: Destruction of the posterior root ganglion combined with axonal and demyelinative peripheral nerve damage causes progressive sensory symptoms. The neuropathy is subacute or chronic in evolution. Clinically dysaesthesia and numbness starts in extremities and spreads. Associated with SCLC and anti-Hu antibodies. Sensorimotor neuropathy. A mixed neuropathy with weakness and sensory loss. The syndrome may predate the recognition of the underlying neoplasm. Rate of progression is slow and predominantly motor forms may be mistaken for ALS (page 535) associated with Hodgkin's and other lymphomas. Rarely an acute neuropathy indistinguishable from postinfectious polyneuropathy occurs. NECROTISING MYELOPATHY:

Flaccid paraplegia develops subacutely. Spinal MRI may show a swollen cord. Mechanism is uncertian. Associated with lymphoma and leukaemia.

MYOPATHY

Muscle weakness in malignancy takes several forms.

Proximal myopathy: A slowly progressive syndrome with weakness of proximal limb muscles. Inflammatory myopathy (polymyositis/dermatomyositis) (see page 456):

The overall incidence of associated neoplasm in inflammatory myopathy is 15%. The typical patient is in middle age with a proximal weakness, elevated ESR and muscle enzymes with or without the skin features of dermatomyositis.

Myopathy with endocrine disturbance: Ectopic hormone production (by malignant cells) may induce a myopathy characterised by chronic progressive proximal weakness, e.g. ectopic ACTH production from small cell carcinoma of lung.

Cachetic myopathy occurs in terminally ill, wasted patients.

In all suspected non-metastatic syndromes, a search for the causal tumour is essential (pelvic CT/ ultrasound, CT chest ¬°bronchoscopy). Identification and treatment may result in regression of neurological symptoms.

Specific treatments

Apart from direct treatment of the tumour, immunotherapy - steroids, IVIG, cyclophosphamide, plasmapheresis have all been tried in deteriorating patients with variable success.

THE MYASTHENIC SYNDROME (Eaton-Lambert syndrome) A disorder of the neuromuscular junction in which antibodies develop against Ca2 ' channels on the presynaptic membrane.

Acetycholine release following nerve stimulation is deficient.-----

This autoimmune disease is occasionally associated with malignancy.

Clinical features

The patient develops weakness of lower then upper limbs with a tendency to fatigue. Following brief exercise, power may paradoxically suddenly improve - second wind phenomenon. In contrast to myasthenia gravis ocular and bulbar muscles are rarely affected. Examination reveals a proximal pattern of wasting and weakness with diminished tendon reflexes. Up to 50% of patients experience symptoms of autonomic (cholinergic) dysfunction -impotence, dry mouth and visual disturbance.

Diagnosis

Confirmed electrophysiologically; the 'second wind phenomenon' is shown up as an incrementing response to repetitive nerve stimulation (as opposed to the decrementing response in myasthenia gravis, page 463). Antibodies to Ca gated channels are detected in serum.

Treatment

Guanidine hydrochloride and 4-aminopyridine enhance acetylcholine release by acting on calcium and potassium channels. These treatments are effective but toxic. 3, 4-diaminopyridine (less toxic), steroids, anticholinesterases, plasmapheresis or IVIG may help.

This syndrome may respond to the removal of the underlying neoplasm if present. 529

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