Polymyositis associated with hypothyroidism or hyperthyroidism: two cases and review of the literature

Studies confirming a possible relationship of polymyositis within thyroid dysfunction, either hypothyroidism or hyperthyroidism, are hardly available. To define the association, identify clinical, laboratory, electromyographic, and pathologic features in polymyositis (PM) patients with hypothyroidism or hyperthyroidism, we conducted a MEDLINE and Chinese biomedicine database search to identify relevant literature published in the past 25 years. Seventeen cases were included. All patients were female (10 hypothyroidism patients, seven hyperthyroidism patients). The mean (SD) age of PM, hypothyroidism, and hyperthyroidism at diagnosis was 54.8 (16.7), 55.5 (16.5), and 32.7 years (10.2), respectively. PM diagnosis can precede or parallel hypothyroidism while PM may occur following the diagnosis of hyperthyroidism. The most common comorbidities were malignant tumors in these disorders, including thymoma, colon cancer, and thyroid cancer. Muscle weakness was described in 100% of patients. Other common manifestations included muscles' atrophy and pain, deep tendon reflexes, polyarthralgia, and dysphagia. Most patients had markedly elevated creatine kinase and the presence of anti-Sjogren's syndrome A (SSA) antibodies was also found in two cases. Malignancy associated with PM may more frequently occur in hypothyroidism than in hyperthyroidism. The abnormalities on electromyography and biopsy did not differ from those findings of PM. Therapy consisting of corticosteroids, thyroid hormone, or anti-thyroid drugs was administrated; however, poor prognosis seemed to be associated with malignant tumors as well as older age and the presence of anti-SSA antibodies. It is reasonable to suggest that those patients should be routinely evaluated for thyroid function, especially in older female and patients suffering from cancers.