Dual pathology: paraneoplastic sarcoidosis emerging at the time of progression from smouldering to symptomatic myeloma.

Sarcoidosis is a systemic disease of unknown aetiology, which is diagnosed based on the presence of non-caseating granulomas on histology. The occurrence of sarcoidosis or a sarcoidosis-like reaction with malignancy has been recognised for several years. Although it has been established that there is an increased risk of lymphoproliferative disorder with sarcoidosis, the association between multiple myeloma and sarcoidosis has rarely been reported. Here, we report the case of woman in her mid-50s with an established diagnosis of smouldering myeloma, who presented with gradually worsening shortness of breath and fatigue after 15 months of active observation. A CT scan of her thorax showed mediastinal lymphadenopathy and the nodes were metabolically active on positron emission tomography CT scan. Endobronchial ultrasound with transbronchial needle aspiration confirmed the diagnosis of sarcoidosis. Further evaluation showed preserved lung function on spirometry. Blood analysis showed a simultaneous rise in the serum lambda-free light chain level from 377 mg/L at initial diagnosis up to 807 mg/L with the kappa/lambda ratio falling to 0.012. Repeat bone marrow aspirate and trephine biopsy showed a 15%-20% infiltrate of lambda light chain-restricted plasma cells with aberrant cyclin D1 expression and abundant sarcoid-like non-necrotising giant cell granulomata. Thus, a diagnosis of paraneoplastic sarcoidosis was established.