Cancer-associated myositis: clinical features and prognostic signs

Idiopathic inflammatory myositis is characterized by progressive weakness of the proximal muscles. There is a higher risk of malignancy than in the normal population. The aim of this study was to evaluate the frequency of malignancy among 251 myositis patients. We also compared clinical and immunological characteristics of cancer-associated myositis with primary myositis. There were no malignancies among polymyositis, overlap, or juvenile myositis patients. Twenty-two of ninety dermatomyositis patients also had a malignant disease. Patients with cancer-associated dermatomyositis were significantly older than primary myositis patients and had more severe cutaneous and muscle symptoms. Dysphagia and diaphragmatic involvement were more frequent among cancer-associated patients, while extramuscular features were less frequent. After successful treatment of the malignancy, we were able to manage myositis symptoms. One-year survival rate was significantly better in primary dermatomyositis patients. The subset of cancer-associated myositis differs from primary myositis in many aspects of its clinical and immunological features. Prognosis and life expectancy in cancer-associated myositis patients is determined by the underlying malignant disease. Therefore, age- and sex-specific examinations for detection of an underlying malignancy are important in the management of patients with dermatomyositis.