Dermatomyositis presenting as a paraneoplastic syndrome due to underlying breast cancer

Breast cancer most often presents as a palpable mass or with an abnormal mammogram. Much less commonly, breast cancer may present as a paraneoplastic syndrome. Dermatomyositis (DM) is a rare disease most often considered a complement-mediated idiopathic inflammatory myopathy manifested by classic skin findings and proximal muscle weakness. However, DM may also be due to a paraneoplastic syndrome associated with an underlying malignancy. The authors present a case report of a woman with presumed contact dermatitis who was diagnosed with breast cancer in the setting of progressive fatigue and muscle weakness. DM was subsequently diagnosed. Treatment of DM simultaneous with treatment of the breast cancer led to regression of DM. The diagnosis of DM in an adult should raise suspicion of an underlying malignancy. Breast cancer is a common disease that may rarely present with uncommon features that may divert attention from the underlying malignancy.