Paraneoplastic necrotizing myopathy presenting as severe muscle weakness in a patient with small-cell lung cancer: successful response to chemoradiation therapy.

Paraneoplastic syndromes (PNS) are defined as clinical syndromes caused by systemic effects of malignancy that are not due to direct physical effects of metastasis. The pathophysiology of PNS is not fully understood; it may result from antibodies against tumors that cross-react with normal tissues, causing injury, or injury induced by humoral factors secreted by tumor cells. PNS may fall into 1 of 4 categories: endocrine, neuromuscular, mucocutaneous, or hematologic. PNS in lung cancers include syndrome of inappropriate secretion of antidiuretic hormone (SIADH), Cushing’s syndrome, hypercalcemia, Lambert-Eaton myasthenic syndrome, and rarely necrotizing myopathy. Clinically obvious muscle weakness can occur in lung cancer patients; however, for the diagnosis of necrotizing myopathy (manifesting usually as symmetric and predominantly proximal muscle weakness), biopsy confirmation becomes essential. Tai and colleagues1 studied 1,417 patients with several histologic types of lung cancers, among which 244 patients had small-cell lung cancer (SCLC) with limited-stage disease. Fourteen of these 244 patients had SIADH at presentation, and 2 of these 14 patients also had PNS manifesting clinically as muscle weakness; however, no biopsy was performed to document the underlying cause of muscle weakness. In another study by Gomm and associates,2 muscle weakness with biopsy-proven necrotizing myopathy was reported to occur in 12 of 100 patients with lung cancers; however, there was no documentation whether any of these patients had SCLC. Levin and coauthors3 reported biopsy-proven