Mycobacterial arthritis as a complication of a Bacille Calmette-Guérin (BCG) vaccination in an immunocompetent child

A 17 month old boy presented with monoarthritis involving his knee, which started 7 month earlier, responding to NSAID therapy, respectively. On physical examination the only finding was the painful effusion and functional limitation of the right knee, with hyperaemic skin reaction above it. His BCG scar was normal. Laboratory evaluation showed mildly elevated CRP (21 mg/l) and C3. RF, ANA, ENA and serological tests for infections were unrevealing. X-ray showed bony owergrowth of the distal femoral epyphisis without osteomyelitis. Ultrasound and MRI of the knee showed intraand extraarticular effusion. Aspirates were turbid with 95% of polymorphs and were sterile with culture, no presence of acid-fast bacilli were detected. Further culture identified BCG vaccine strain of M. bovis. Twelve weeks of isoniacid therapy was ineffective, surgical bursectomy gave a complete healing. Histological examination revealed granulomatous inflammation with ceasating necrosis. Hypererg PPD test, normal T-cell functions, NBT-test and analysis of the IFNγ/IL-12 pathway ruled out primary immunodeficiency, HIV-test was negative as well.