Paraneoplastic Syndromes

The extrathoracic paraneoplastic syndromes are neuroendocrine phenomena associated with lung carcinoma. These include the following:

1) Cushing's syndrome. Those patients with this syndrome are patients with small cell carcinoma who produce a large amount of ACTH. Dexamethasone fails to suppress the levels of ACTH and hence Cushing's syndrome secondary to lung carcinoma is distinguishable from a pituitary tumor producing ACTH which is suppressed by Dexamethasone. The signs and symptoms of the syndrome may be suppressed by appropriate chemotherapy for small cell cancer.

2) Inappropriate ADH production. The symptoms are water intoxication with nausea and vomiting and worsening neurologic complications secondary to hy-ponatremia. This occurs most often in patients with small cell lung cancer.

3) Hypercalcemia caused by PTH-like polypeptide has most often been associated with squamous cell carcinoma. Hypercalcemia usually represents bony metastases, however, it may be caused by secretion of the PTH like hormone.

4) Myasthenia-like syndrome is due to a defect in neuromuscular conduction a similar to that in myasthenia gravis but is found in patients with bronchogenic carcinoma. It is due to antibodies against the acetylcholine receptor produced by

the tumor. This myasthenia-like syndrome is called the Eaton-Lambert syndrome.

5) Carcinoid syndrome. This has been reported in a few patients with oat cell carcinoma secondary to amine secretion by the tumor.

In addition to the above mentioned myasthenia-like Eaton-Lambert syndrome, other neuromuscular manifestations include polymyositis, peripheral neuropathy, encephalomyelopathy and cerebellar degeneration. Other manifestations include skeletal manifestations with generalized hypertrophic pulmonary osteoarthropathy with periosteal proliferation and new bone formation. The incidence has been reported to be between 2 and 12%; however, this phenomenon is not found in patients with small cell tumors, although its incidence in patients with the other three major cell types was equally distributed.

Dermatologic manifestations include acanthosis nigricans which may be associated with adenocarcinoma. Other manifestations include thrombophlebitis and may be considered part of the generalized Trousseau syndrome of hypercoagu-lable state associated with neoplasia.

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