Primary thyroid lymphoma presenting as dermatomyositis: a first case and review of the literature.

A 55-year-old woman presented with a 3-week history of weakness. On examination, she had a heliotrope rash, V-neck and shawl signs. There was symmetric proximal muscle weakness, and 2/5 strength in upper and lower extremities. Laboratory values showed CK 5836, CRP 14.9, erythrocyte sedimentation rate 49, lactate dehydrogenase 633, negative antinuclear antibodies and anti-Jo1 antibodies. Muscle biopsy and immunohistochemistry findings were consistent with dermatomyositis. Treatment with high-dose steroids, cyclophosphamide and intravenous immunoglobulin (IVIG) was started, without improvement of symptoms. She was found to have cold agglutinins with a cold screen titre of 1:256,256. Work up for malignancy ensued. Positron emission tomography-computed tomography (PET-CT) showed increased uptake in the thyroid. Fine-needle thyroid biopsy with flow cytometry studies revealed atypical lymphocytes consistent with diffuse large B-cell lymphoma. The patient underwent R-CHOP therapy, with remarkable improvement of her symptoms. Dermatomyositis associated with primary thyroid lymphoma has not been previously reported. This case reinforces the importance of cancer screening in dermatomyositis patients.