Atypical sarcoidosis diagnosed by bone marrow biopsy during renal workup for possible multiple myeloma

Sarcoidosis is a multi-organ disease of unknown etiology characterized by non-caseating granulomas. Here we report the case of a 78-year-old white male with a past medical history of diabetes mellitus, hypertension, and chronic kidney disease stage III with a baseline serum creatinine of 2.5 mg/dl. The patient had a prior admission history for acute kidney injury (AKI) attributed to dehydration and medication-induced nephro-toxicities. He presented to the renal clinic for follow-up with acute worsening of chronic kidney failure with a serum creatinine level of 3.5 mg/dl. Examination revealed that he was anemic and mildly hypercalcemic with suppressed parathyroid hormone and had proteinuria of 1.3 g per day. The computed tomography scan of the abdomen revealed right renal pelvic non-obstructing calculi. Serum protein electrophoresis revealed gammopathy with two distinct monoclonal peaks consisting of immunoglobulin G (IgG) kappa and IgG lambda, respectively. The kappa/lambda ratio was within normal limits, and urine protein electrophoresis showed no evidence of a monoclonal peak or Bence Jones proteins. Further workup for multiple myeloma, including bone marrow (BM) biopsy, revealed polyclonal plasma cells and B cells with no clonality. No morphological and immune-phenotypic evidence of plasma cell dyscrasia was found, but BM biopsy did show numerous non-caseating granulomas consistent with sarcoidosis. Skin biopsy from non-scaly 6-mm skin colored papule also showed non-caseating granulomas. The patient had elevated angiotensin-converting enzyme levels (165 ug/l) and an erythrocyte sedimentation rate of 27 mm/h. Kidney biopsy did not show granulomas. The hypercalcemia, proteinuria, and AKI responded well after 2 weeks of 60 mg oral prednisone daily.