Insidious osteomyelitis in kids under 2 years may turn out to be BCG-osteomyelitis

Yuko Tsujioka et al conducted a retrospective study to report the clinical and imaging characteristics of BCG-osteomyelitis, and compare them with those of pyogenic osteomyelitis at the following japan institutes - Tokyo Metropolitan Children's Medical Center , National Center for Child Health and Development and St. Luke's International Hospital.

Recent reports have shown that the incidence has increased worldwide; thus, a number of affected individuals may not have been precisely diagnosed because of its rarity and lack of attention from healthcare professionals; yet, the prompt introduction of antituberculous therapy could prevent the late morbidities, such as leg length discrepancy and joint deformity. Hence, the early diagnosis and timely medical intervention are desirable, but the diagnosis of BCG-osteomyelitis rests on a physician's suspicion, because the routine histological examination alone may not lead to an unequivocal diagnosis.

Clinical and imaging findings were retrospectively evaluated in 14 children with BCG osteomyelitis, including 3 with Mendelian susceptibility to mycobacterial diseases (MSMD), and in 40 children with pyogenic osteomyelitis, using Fisher exact and Mann-Whitney U tests.

The observations in the study were:

• BCG-osteomyelitis was an indolent inflammatory disease of young children (mean age 15.5 months).

• Immunocompetent patients came to medical attention over months after vaccination, while patients with MSMD much earlier (the average time lapse: 13.7 vs. 5.0 months). The former manifested with a slowly progressive, painless mass with only mildly increased acute-phase reactants, while the latter started with lymphadenitis with significant inflammatory reactions and later developed osteomyelitis. These clinical scenarios contrasted with acute febrile illness in pyogenic osteomyelitis.

• The imaging findings were identical in both immunocompetent and MSMD groups; however, the former showed monoostotic involvement, while the latter polyostotic affiction.

• The typical imaging finding of BCG-osteomyelitis comprises a large intraosseous abscess with modest reactive edema commonly associated with transphyseal extension from the metaphysis to the epiphysis, contrasting with the manifestation of pyogenic osteomyelitis; size of abscess (p=0.028), pattern of abscess extension (p<0.001), and extent of surrounding edema (p<0.001).

This retrospective study has a few drawbacks, including a limited number of cases, institution-related selection bias, laboratory data and imaging obtained at various stages of the disease, and inconsistent MRI imaging sequences. Further studies on multi-institutional and/or large international cohorts are desirable to understand the full spectrum of the clinical and imaging features in BCG osteomyelitis.

The authors concluded that - BCG-osteomyelitis should be suspected in children under 2 years of age with insidious osteomyelitis, accompanied with characteristic imaging findings. Polyostotic BCG osteomyelitis is highly suggestive of MSMD. Awareness of the distinctive features of BCG-osteomyelitis enables the early diagnosis and timely therapeutic intervention.

Further reading:

BCG osteomyelitis: tips for diagnosis

Yuko Tsujioka, Taiki Nozaki, Gen Nishimura, Osamu Miyazaki, Masahiro Jinzaki, Tatsuo Kono

Skeletal Radiology (2022) 51:1571–1584

https://doi.org/10.1007/s00256-021-03966-7