Neuromuscular syndromes associated with malignant disease.

Malignant disorders may produce neuromuscular syndromes in a variety of ways, for some of which it is still difficult to determine the exact pathophysiology. In the myopathic and neuropathic disorders, one possible explanation is that they are due to a virus such as is found in the rare "progressive multifocal leukoencephalopathy". This is seen in association with the malignant lymphomas and with other conditions such as sarcoidosis where immune responses may be altered by either the disease or the treatment. No viral material has been found in the nonmetastatic neurological disorders apart from progressive multifocal leukoencephalopathy. An alternative theory is that there may be an autoimmune process, the nervous system sharing some antigenic determinant with the neoplasm (Urich, 1967). The prognosis in the paraneoplastic neurological disorders is usually poor. As well as the direct threat to life posed by the malignant disease, when the neurological disorder is due to destruction of neurones (for instance cerebellar degeneration or sensory neuronopathy) recovery of function is impossible. Spontaneous remissions have been recorded in cases of proximal muscle weakness and sensorimotor neuropathy, but it is difficult to know whether the remissions have been truly spontaneous or related to treatment (excision of the neoplasm or administration of steroids). Further immunological and virological studies will probably reveal the answers to some of the outstanding problems. In the meantime the clinician must continue to investigate patients with muscular weakness for evidence of an occult neoplasm, and to repeat investigations if no other cause for the neurological disorder is found. Also, in patients with known malignant disease, apart from trying to differentiate forms of neuromyopathy from the effects of metastases the various metabolic disorders must be considered because the therapeutic possibilities are a little more promising in the paraneoplastic endocrine disorders. Ross (1975) wisely said that "cancer has replaced syphilis as the great imitator".