Mycobacterium xenopi osteomyelitis of the spine: a case report
Keywords:Mycobacterium xenopi osteomyelitis, tuberculosis, anti-tuberculosis treatment
Mycobacterium xenopi (M. xenopi) osteomyelitis is an uncommon infection which is found in immunosuppressed patients. It is reported to be a slow-growing, nonchromogenic or scotochromogenic nontuberculous mycobacterium. The lungs constitute the most common site for infection and extrapulmonary manifestations, and disseminated forms of the disease are rare. Only a few cases of spontaneous spinal involvement have been reported. We report a case of M. xenopi vertebral osteomyelitis of the spine.
Patient and methods
A 41-year-old female patient, HIV reactive on antiretroviral therapy with a low CD4 count of 183 cells/mm3, presented with clinical and radiological features in keeping with thoracic spinal tuberculosis, complicated with thoracic myelopathy. She was managed surgically with costotransversectomy and drainage of the paraspinal cold abscess. The Ziehl–Neelsen staining was negative for acid-fast bacilli. However, the histology result revealed a necrotising granulomatous inflammation. A delayed result of polymerase chain reaction (PCR)/line probe assay for Mycobacterium genus testing revealed the presence of M. xenopi, as the cause for the spine osteomyelitis and thoracic myelopathy. However, no M. xenopi susceptibility testing, and no specific photoreactivity techniques for strain identification, were performed. Anti tuberculosis therapy (ATT) consisting of a two-month initiation phase using rifampicin, isoniazid, ethambutol and pyrazinamide, followed by a seven-month continuation phase using rifampicin and isoniazid, was initiated according to national guidelines. She was fitted with a thoraco-lumbar-sacral orthosis, and underwent a spinal rehabilitation programme. Upon receipt of the PCR result, and considering the good clinical and radiological response to ATT, a consensus was reached with the Infectious Disease Unit (IDU) to continue with ATT until 18 months due to the atypical nature of the pathogen.
The patient was successfully treated with the standard TB regimen, but for a period of 18 months, and made full clinical neurological recovery, without any back pain. Furthermore, her CD4 count had also improved to 707 cells/mm3 with a viral load reported lower than 1 000 copies/ml.
This case report emphasises the importance of biopsy in suspected spinal tuberculosis and highlights the concerns with laboratory testing and the prognostic and therapeutic implications of a positive strain identification.
Level of evidence: Level 5