Dermatomyositis associated with cancer of unknown primary site.

Dermatomyositis (DM) is an uncommon inflammatory myopathy with characteristic rash accompanying, or more often preceding, muscle weakness. There is a well-recognized association between DM and several cancers, such as ovarian cancer, breast cancer, melanoma, colon cancer, and non-Hodgkin lymphoma. We report the first case of cancer of unknown primary site associated with DM. A 62-yr-old woman presented to us with both shoulder painful swelling and facial edema. She was diagnosed previously as cancer of unknown primary site, histologically confirmed with squamous cell carcinoma in a pelvic mass. For the following days, she complained of erythematous face followed by progressive weakness of the proximal muscles of upper and lower limbs. The laboratory tests showed an increased muscle enzyme and acute phase reactants. The electromyogram showed the typical findings of DM. After the treatment with high dose steroid and methotrexate, the proximal motor weakness improved, and she received palliative radiation therapy.