Concurrent Diabetic Muscle Infarction and JAK2 Exon 12-Positive Polycythemia Vera: A Rare Dual Diagnosis.

Diabetic muscle infarction (DMI) is an uncommon and frequently underrecognized microvascular complication of longstanding diabetes mellitus characterized by spontaneous ischemic necrosis of skeletal muscle. Polycythemia vera (PV) associated with JAK2 exon 12 mutations represents a rare subtype of myeloproliferative neoplasm that typically presents with isolated erythrocytosis and suppressed serum erythropoietin levels. The coexistence of these two uncommon disorders is exceptionally rare and may create significant diagnostic challenges because painful limb swelling can mimic thrombotic, infectious, inflammatory, or neoplastic conditions. We report the case of a 52-year-old man with poorly controlled type 2 diabetes mellitus who presented with a 3-week history of progressive atraumatic pain and swelling of the left thigh. Doppler ultrasonography excluded deep vein thrombosis and abscess formation, while magnetic resonance imaging demonstrated diffuse muscle edema, short tau inversion recovery (STIR) hyperintensity, and characteristic findings consistent with DMI. Laboratory investigations revealed marked erythrocytosis (hemoglobin 19.9 g/dL), thrombocytosis, and suppressed serum erythropoietin levels. Bone marrow examination demonstrated hypercellularity with erythroid predominance, and molecular testing identified a JAK2 exon 12 mutation, fulfilling contemporary diagnostic criteria for polycythemia vera. Conservative management of DMI together with therapeutic phlebotomy for PV resulted in progressive clinical improvement. This case highlights the importance of maintaining a broad differential diagnosis when evaluating painful limb swelling in patients with diabetes mellitus and persistent erythrocytosis. Recognition of coexisting disorders through careful integration of clinical assessment, imaging, and hematological investigation allows timely diagnosis, avoids unnecessary invasive procedures, and facilitates appropriate disease-specific management.