A Case of Hairy Cell Leukemia in a Patient with Sarcoidosis: Diagnostic and Treatment Challenges

Hairy cell leukemia (HCL) is a rare B-cell malignancy that can presentdiagnostic challenges when coexisting with other conditions. Sarcoidosis,a multisystem granulomatous disease, shares several overlapping clinicalfeatures with HCL, complicating timely diagnosis and treatment initiation.We present a case of a 44-year-old male with a history of sarcoidosis and mildnormocytic anemia who developed worsening cytopenias and splenomegaly aftera severe COVID-19 infection. Initial hematologic abnormalities were attributedto sarcoidosis-related inflammation and post-viral bone marrow suppression.However, persistent anemia and thrombocytopenia led to further evaluation,revealing atypical lymphocytes with “hairy” projections. Bone marrow biopsyconfirmed HCL with the BRAF V600E mutation. First-line treatment resultedin partial remission, but residual disease persisted. The patient relapsed andwas successfully treated with targeted therapy, achieving sustained completeremission for over a year.The co-occurrence of HCL and sarcoidosis presents a unique diagnosticchallenge. This case highlights the diagnostic complexity of HCL in the settingof pre-existing sarcoidosis and recent severe infection. Given their overlappingclinical manifestations, distinguishing between the two conditions is crucial toprevent delays in appropriate treatment.Keywords: Hairy cell leukemia; Sarcoidosis; Pancytopenia; Targeted therapy