Chest wall abscess with sternal osteomyelitis as an unusual complication following Bacillus Calmette-Guérin (BCG) vaccination in an infant: A case report.

Chest wall abscess with sternal osteomyelitis is an uncommon but serious complication following Bacillus Calmette-Guérin (BCG) vaccination in infants. We report a previously healthy 6-month-old male who presented with a lobulated, progressively enlarging mass on the left anterior chest wall, 2 months after receiving BCG vaccination at birth. The lesion was unresponsive to antibiotic therapy, and there was no history of tuberculosis exposure. Chest magnetic resonance imaging demonstrated a lobulated, enhancing lesion in the anterior chest wall, consistent with abscess and osteomyelitis, while neoplasm was also considered in the differential diagnosis. Tissue biopsy confirmed Mycobacterium bovis BCG strain by line probe assay, whereas histopathology was nonspecific and negative for malignancy. Immunologic evaluation revealed no evidence of immunodeficiency. The patient was treated with a 2-month regimen of isoniazid, rifampicin, and ethambutol, followed by 10 months of isoniazid and rifampicin. Although clinical improvement was observed at the 1-year follow-up, a residual abscess of reduced size and thoracic deformity persisted, prompting consideration of extended therapy. This case underscores the importance of maintaining a high index of suspicion for BCG-related osteomyelitis even in immunocompetent infants and emphasizes the essential role of molecular diagnostics in facilitating early diagnosis and improving clinical outcomes.