A Hematologic Mimic: Sarcoidosis Presenting With Myelodysplastic Syndrome-Like Marrow Dysplasia, Massive Splenomegaly, and Pancytopenia.

Sarcoidosis is a multisystem granulomatous disorder of unknown etiology with heterogeneous clinical manifestations and significant diagnostic challenges, particularly when extrapulmonary involvement predominates. Although splenic, hematologic, metabolic, and lymphatic manifestations are individually recognized, their simultaneous occurrence is exceptionally rare. We report a diagnostically complex case of sarcoidosis presenting with massive splenomegaly, pancytopenia, parathyroid hormone-independent hypercalcemia with renal dysfunction, and bone marrow findings suggestive of myelodysplastic syndrome. A 53-year-old man was incidentally found to have pancytopenia during routine evaluation and was asymptomatic at presentation, without constitutional symptoms. Abdominal imaging revealed massive splenomegaly with preserved hepatic morphology. Bone marrow aspiration and biopsy demonstrated multilineage dysplasia with low blast percentage, favoring myelodysplastic neoplasia; however, this diagnosis was discordant with the presence of massive splenomegaly. Subsequent biochemical evaluation revealed hypercalcemia with suppressed parathyroid hormone levels and associated renal dysfunction, prompting further investigation. 18F-fluorodeoxyglucose positron emission tomography-computed tomography demonstrated extensive FDG-avid mediastinal, hilar, cervical, and abdominal lymphadenopathy with gross splenomegaly, a pattern suggestive of granulomatous disease. Elevated serum angiotensin-converting enzyme levels supported this impression. Definitive diagnosis was established by excisional cervical lymph node biopsy, which revealed non-caseating granulomatous lymphadenitis consistent with sarcoidosis. This case illustrates a rare and misleading presentation of sarcoidosis that closely mimicked a primary hematologic disorder. It underscores the importance of maintaining a broad differential diagnosis and emphasizes the critical role of integrated clinicopathologic correlation and tissue confirmation in patients presenting with unexplained cytopenias and massive splenomegaly.