Diffuse skeletal and bone marrow metastases mimicking plasma cell dyscrasia in advanced lung adenocarcinoma.

A man in his late 40s presented with progressive chest pain, cough and dyspnoea. Imaging revealed left lung collapse with pleural involvement. Thoracoscopic pleural biopsy confirmed pulmonary adenocarcinoma by immunohistochemistry. Staging fluorodeoxyglucose positron emission tomography-CT demonstrated nodal disease and unexpectedly diffuse marrow uptake with widespread lytic lesions involving the axial and appendicular skeleton, raising concern for a haematological malignancy. Serum protein electrophoresis revealed no monoclonal band, arguing against plasma cell dyscrasia. CT of the brain demonstrated multiple lytic calvarial lesions without parenchymal involvement, an unusual pattern in lung adenocarcinoma. The patient was diagnosed with stage IV lung adenocarcinoma with extensive skeletal metastases. Owing to poor performance status and advanced disease, the patient was managed with the best supportive care and died 5 months after diagnosis. This case highlights that lung adenocarcinoma may rarely present with diffuse marrow involvement and highlights the importance of histopathological correlation when imaging mimics haematological disease.