A tricky trochanter

A 24-year-old previously well female presented with a discharging thigh abscess after travel to Ghana. She reported malaise but was otherwise systemically well. Further history revealed 2 years of intermittent left thigh pain, which had been attributed to a large trochanteric bursa identified on ultrasound in 2017. On examination she was afebrile with a deep, undermined ulcer discharging pus in the left antero-lateral thigh. Femoral X-ray was unremarkable.

She underwent surgical debridement and intra-operatively infection was found to track to the greater trochanter. Tissue specimens grew Gemella morbillorum, Klebsiella pneumoniae, Enterobacter cloacae, Streptococcus anginosus and mixed anaerobes. She responded well to 4 weeks of ciprofloxacin, metronidazole and amoxicillin. Histological examination of the ulcer edge revealed non-necrotising granulomata (Ziehl-Neelsen stain negative).Mycobacterium tuberculosis(MTB) was subsequently isolated on mycobacterial culture from the same site. MRI demonstrated osteomyelitis of the greater trochanter with a 2cm intramedullary abscess and an adjacent soft tissue collection. Macroscopically caseous material was found on further debridement and tissue samples were AAFB smear negative but MTB complex was detected by PCR and culture of intra-medullary bone.

This case demonstrates that bacteria and mycobacteria may be co-pathogens, and that M. tuberculosis bone infection may present with no systemic symptoms. It is a reminder of the importance of cross-sectional imaging and mycobacterial culture in deep soft tissue infections with a long or unusual history.