A70-36 Tuberculous Osteomyelitis of the Proximal Tibia Mimicking a Bone Tumor in a Young Man: A Diagnostic Challenge

Abstract Introduction Extrapulmonary tuberculosis (TB) can involve various organ systems; musculoskeletal TB is an uncommon manifestation accounting for only 1-5% of all TB cases. Among skeletal TB, Pott’s disease is most frequent, whereas long bone osteomyelitis, especially of the tibia, is rare. This case exemplifies these challenges and highlights the need for high clinical suspicion when evaluating atypical bone lesions. Case An 18-year-old male presented with a six-month history of a progressively enlarging, painful mass on the left proximal tibia. He had no history of trauma or chronic illness. Initial orthopedic assessment suggested a primary bone tumor, most likely a giant cell tumor. X-ray and MRI findings showed an intraosseous lesion proximal tibia. He was treated with ciprofloxacin for one month following Staphylococcus aureus growth from pus culture; however, no improvement occurred. He later developed intermittent night sweats, appetite loss, and a 4-kg weight loss. Examination revealed a firm, warm, immobile 5 × 5 cm mass over the left knee, with tenderness and limited flexion. Laboratory tests showed an elevated erythrocyte sedimentation rate of 57 mm/h and a C-reactive protein level of 3.84 mg/dL. Chest radiography was normal. Surgical biopsy, debridement, and curettage revealed an intraosseous abscess and cortical bone defect. Histopathology demonstrated granulomatous inflammation with multinucleated giant cells and caseous necrosis, consistent with tuberculous osteomyelitis. The patient resided in a TB-exposed boarding school. His mother and his sibling had previously completed treatment for pulmonary TB and lymphadenitis, respectively. He received anti-tuberculosis treatment for nine months. The patient showed marked clinical improvement. Discussion Tuberculous osteomyelitis of long bones such as the tibia is uncommon and may closely mimic primary bone tumors clinically and radiologically. The proximal tibial lesion was initially misdiagnosed as a bone tumor. Microbiological confirmation was challenging; AFB smears and M. tuberculosis PCR were negative, reflecting the paucibacillary nature of skeletal TB; therefore, definitive diagnosis relied on histopathological evidence of granulomatous inflammation from surgical biopsy. TB usually spreads hematogenously from the lungs or lymph nodes; this case in an immunocompetent young male with normal lungs underscores that osteoarticular TB can occur independently of pulmonary disease. Close household and boarding-school exposure to active tuberculosis cases likely contributed to latent infection and subsequent reactivation. Thus, early histopathologic evaluation supported by clinical, imaging, and epidemiologic assessment remains essential to distinguish tuberculous osteomyelitis from malignancy and ensure timely anti-tuberculosis therapy. This abstract is funded by: None