Hematologic abnormalities in young adults are frequently attributed to infections or reactive processes, yet concurrent cytopenias and lymphocytosis may herald malignant conditions. Acute lymphoblastic leukemia (ALL) is uncommon in adults but should be considered in the presence of persistent unexplained hematologic abnormalities (Inaba et al., 2021). Here, we present a 29-year-old male patient initially hospitalized with myocarditis, in whom incidental hematologic findings prompted further investigation and ultimately led to the diagnosis of precursor B-cell acute lymphoblastic leukemia (B-ALL), Türkiye.

The patient, with comorbid obesity, hyperlipidemia, prediabetes, and coronary artery disease, was admitted to the coronary intensive care unit due to myocarditis. Laboratory evaluation revealed neutropenia, lymphocytosis, anemia, and severe thrombocytopenia. Hematology consultation was obtained, and systematic infectious and metabolic workup was performed, including TORCH, hepatitis panel, HIV, brucella, and syphilis, all of which were negative. Nutritional deficiencies were excluded. Bone marrow aspiration and biopsy were conducted to clarify the unexplained cytopenias.

Peripheral smear showed marked lymphocytosis. Bone marrow evaluation demonstrated precursor B-cell blasts consistent with B-ALL. The patient had a prior history of episodic polycythemia treated with phlebotomy at an external center, but no prior evaluation for myeloproliferative neoplasm was documented. Physical examination was remarkable for obesity and cervical lymphadenopathy. Despite the confirmed diagnosis of B-ALL, the patient declined further therapy and left the clinic against medical advice.

This case underscores the diagnostic challenge posed by overlapping cardiac and hematologic findings. While myocarditis can present with systemic manifestations that mimic hematologic disorders, persistent cytopenias with lymphocytosis should prompt early hematology evaluation (Terwilliger & Abdul-Hay, 2017). Adult B-ALL often carries a poor prognosis compared to pediatric cases, and early initiation of therapy is critical to improving outcomes (Kantarjian et al., 2017). Moreover, this case highlights the importance of considering hematologic malignancy in young adults with incidental laboratory abnormalities, even in the context of alternative explanations such as infection or cardiac disease. Systematic diagnostic workup, including bone marrow biopsy, remains the gold standard for definitive diagnosis (Hunger & Mullighan, 2015).

We report a young adult male followed for myocarditis in whom incidental hematologic abnormalities revealed underlying precursor B-cell ALL. This case emphasizes the necessity of maintaining a broad differential diagnosis in young adults with unexplained cytopenias and lymphocytosis, and of not delaying bone marrow evaluation. Prompt recognition is essential for timely treatment initiation and improved patient outcomes.