| Summary: | Cholangiocarcinoma with paraneoplastic dermatomyositis (DM) is extremely rare, and the whole body positron emission tomography-computed tomography (PET-CT) finding of paraneoplastic DM is rarely reported. We report a 66-year-old woman with metastatic cholangiocarcinoma, initially presented with bilateral proximal muscle uptake on PET-CT without clinical muscle symptoms. The initial interpretation of the high muscle uptake was metastasis to the muscles. However, while awaiting for chemotherapy, muscle weakness evolved and rapidly progressed. The level of creatine phosphokinase was significantly elevated. Electromyography revealed moderate myopathy, and a muscle biopsy showed degenerating myofibers with variable sizes. The diagnosis of paraneoplastic dermatomyositis was made. This case highlights that, although rare, paraneoplastic dermatomyositis can be present with cholangiocarcinoma. Also, muscle inflammation can precede the clinical muscle symptoms, and paraneoplastic DM should be considered as a possible differential diagnosis in the assessment of cancer patients who present with abnormal muscle tracer uptake in PET-CT scans.
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