Granulomas in bone marrow: is it always tuberculosis?

Granulomas in a bone marrow biopsy are like gold dust. Numerous studies have reported that the incidence of granulomas in bone marrow biopsies ranges from 0.3 to 2.2%. In developing countries such as India, tuberculosis is the most common cause of bone marrow granulomas; nonetheless, the etiologic spectrum includes a broad range of disorders. To better understand granulomatous inflammation in the bone marrow and prevent its misinterpretation, this study aims to highlight the variety of disorders, including infectious and non-infectious causes, that are linked to this finding. This is a retrospective study which was conducted in the Department of Pathology and Laboratory Medicine at All India Institute of Medical Sciences, Rishikesh. Bone marrow biopsies with granulomatous inflammation reported over a period of 3 years, from 2022 to 2024, were reviewed for their clinical and laboratory features and included in this study. We identified 22 cases among 3485 bone marrow biopsies, representing an incidence of 0.63% in the series. Among the 22 patients, the most common etiology was infectious (59.1%), followed by malignancy (36.34%), and sarcoidosis (4.5%). Marrow granulomas should prompt a thorough investigation into the underlying cause. It is hoped that this article would help in guiding the investigation for potential causes.