Polymyositis is an inflammatory myopathy of unknown etiology in which the striated muscles are damaged by an inflammatory process dominated by lym-phocytic infiltration. Immunohistochemical studies suggest immunologically mediated muscle damage with accumulation of B and mostly T lymphocytes. There is compelling evidence that the mechanism of paraneoplastic polymyositis relates to the activation of CD8+ T cells that become cytotoxic to a muscle antigen. However, this information is more useful for understanding pathogenesis than for making a diagnosis of the inflammatory muscle process. Polymyositis is associated with 10% of cancer-related paraneoplastic syndrome. The presence of dermatomyositis in an elderly patient may warrant a thorough search for neoplasms including a bladder tumor (Mallon et al. 1999; Apaydin et al. 2002; Rankin and Herman 2002).

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