CLINICAL CASE OF THE MONTH. A 63-Year-Old Woman With Rash and Proximal Muscle Weakness.

A 63-year-old woman with a history of infiltrating ductal breast cancer, status post-mastectomy and chemotherapy, was in remission for 18 months prior to being admitted to the hospital with complaints of a pruritic erythematous macular rash involving her head, chest, and bilateral upper and lower extremities. Along with the dermatologic manifestations, physical exam revealed proximal symmetrical muscle weakness and bilateral axillary lymphadenopathy. Initial workup for muscle weakness revealed a creatine kinase of 2,200 IU/L (normal 20-180 IU/L). After administration of intravenous fluids for renal protection, serum sodium dropped to 121 mEQ/L (normal 135-145 mEQ/L). Computed tomography of the chest showed axillary and supraclavicular lymphadenopathy. Biopsy of a supraclavicular node revealed infiltrating ductal cancer with histologic and morphologic characteristics similar to her previous breast cancer. Following an extensive laboratory workup, we concluded that our patient's myositis and hyponatremia were paraneoplastic syndromes secondary to her recurrent breast cancer.