A 12-month-old girl came from Nakornsawan province, who presented with painless progressive palpable round shape mass at the right costal margin. She had no fever. Her appetite was good, but still she had poor weight gain with height and weight both lower than fifth percentile. No history of contact with tuberculosis was found, but her mother had a positive history of TB lymphadenitis and completed treatment more than ten years ago. The natal history was unremarkable. She completed the Thai national immunization program and was given complementary vaccines including pneumococcus, H. influenza, and intradermal tuberculosis vaccine at birth.
Physical examination revealed a 2 cm round fixed firm mass at the right anterior lower chest wall. Bacillus Calmette-Guerin (BCG) scar was found at right upper leg. Otherwise, it was unremarkable. Chest radiograph demonstrated a moth-eaten osteolytic lesion at the right anterior 8th rib, shown in Figure 1. Complete blood count showed the following: hemoglobin: 11.2 (>10.5) g/dL, white blood cell: 12,790 (6,000-17,500)/mcL (N: 20.4%, L: 73.1%), PLT: 339,000/mcL, alkaline phosphatase: 201 (150-420) U/L, and hs-CRP: 20.98 (0-5) mg/L. Chest magnetic resonance imaging (MRI) is shown in Figure 2. The presumptive diagnosis is probable Ewing's sarcoma or Langerhans cell histiocytosis.
Resection of the mass was arranged. Intraoperative examination revealed a firm round 5 cm mass with signs of osteomyelitis on the rib and pus. The pus was further processed and revealed positive acid fast bacilli stain (AFB) and was reactive of polymerase chain reaction (PCR) for Mycobacterium tuberculosis complex (MBTC). Pathology, shown in Figure 3, confirmed caseous granulomatous inflammation compatible with mycobacterial infection. A positive purified protein derivative (PPD) skin test at 72 hours was reported afterward. However, mycobacterial pus culture, QuantiFERON-TB Gold, 3-day morning gastric content for AFB, MTBC PCR, and culture were all negative. Because of clinical and negative QuantiFERON-TB Gold, Mycobacterium bovis (M. bovis) osteitis is highly suspected. She was treated with HRZE standard regimen (isoniazid, rifampicin, pyrazinamide, and ethambutol) for 2 months and switched to HR (isoniazid and rifampicin) for a total of 12 months. Outpatient 3-year follow-up demonstrates excellent weight gain, good appetite, and normal wound healing without mass progression.