Sarcoidosis Masquerading as Malignancy

Introduction: Sarcoidosis is a granulomatous disease that rarely presents with bone involvement mimicking malignancy. We present a diagnostically challenging case of sarcoidosis initially suspected to be metastasis or myeloma due to an incidental MRI finding. Case Description: A 60-year-old woman with HIV, hepatitis B, and rheumatoid arthritis presented with vertigo and memory loss. Brain MRI showed skull lesions concerning for metastases or myeloma. She reported exertional dyspnea and fatigue but denied bone pain, fever, or recent illness. Labs showed no M spike on SPEP, elevated free light chains (kappa 112.9 mg/L, lambda 48.2 mg/L, ratio 2.34), hypercalcemia, elevated creatinine, and high calcitriol (84.5 pg/mL). UA showed trace proteinuria and microhematuria. CT chest showed hilar and mediastinal lymphadenopathy without lung lesions. PET-CT showed mandibular uptake and diffuse marrow activity. Mammogram was negative. Bone marrow (BM) biopsy showed non-necrotizing granulomas (Figures 1/2). Kidney biopsy showed acute tubular injury without granulomatous interstitial nephritis (Figures 3/4). IF and EM were unrevealing. Angiotensin-converting enzyme (ACE) was elevated; TB/fungal studies were negative. She was diagnosed with sarcoidosis and treated with prednisone, hydroxychloroquine, and azathioprine with improvement in labs (Table 1). Discussion: Bone lesions occur in 1-15% of sarcoidosis cases, which remains on the differential for hypercalcemic AKI even when malignancy is suspected. BM granulomas are rare with an incidence of 0.3-2.2%. In this case, hypercalcemia-induced acute tubular injury without granulomatous nephritis made the sarcoidosis-AKI link atypical. Multidisciplinary input enabled prompt diagnosis and therapy.Laboratory studies - Serum Laboratory Test Pre-Treatment 3-Month Follow-Up Serum creatinine 1.46 mg/dL 0.97 mg/dL Serum calcium 11.0 mg/dL 8.8 mg/dL ACE 180 U/L 149 U/L