Case Report: Apixaban induced spontaneous muscular hematoma in a patient with inclusion body myositis

Direct oral anticoagulants, including apixaban, are widely prescribed for stroke prevention in atrial fibrillation. While gastrointestinal and intracranial hemorrhages are the most common adverse events, apixaban can also cause spontaneous intramuscular hematomas which are rare, especially in the absence of trauma or clear predisposing factors. We describe a 69-year-old Caucasian female with a history of hypertension, atrial fibrillation on apixaban, inclusion body myositis, and osteoporosis, who presented with acute onset left flank pain and extensive bruising of one week duration. Initial treatment for presumed musculoskeletal strain was followed by discovery of significant anemia (hemoglobin 8.3 g/dL). Initial Computed Tomography revealed a large posterior flank hematoma (15.9 × 8.2 × 5.5 cm). Despite stable hemodynamics and absence of active extravasation, surgical evacuation was required due to hematoma expansion. Anticoagulation was held during hospitalization, and apixaban discontinuation was recommended postoperatively, with future evaluation for left atrial appendage closure. This case highlights an unusual but serious complication of apixaban therapy. Inclusion body myositis and osteoporosis, associated with drug-drug interactions, chronic inflammation and impaired tissue repair, may have predisposed the patient to spontaneous muscular bleeding. The interplay between neuromuscular disease and DOAC therapy warrants further investigation, particularly in elderly patients with multiple comorbidities. • Apixaban can cause atraumatic intramuscular hematomas in select patients. • Inclusion Body Myositis and bone demineralization may heighten muscular bleeding risk on DOACs. • Early imaging guides diagnosis of unexplained anemia or soft tissue swelling. • Surgical intervention is reserved for large, symptomatic hematomas. • Studies should clarify bleeding risk in inflammatory myopathies on DOACs.