Multifocal Mycobacterium kansasii osteomyelitis in a patient on ruxolitinib

Background Mycobacterium kansasii spinal infection is rare. This is the first reported case in a patient taking ruxolitinib. Case report A 69-year-old woman attended the emergency department with severe debilitating lumbar back pain and right sided flank pain. She had experienced persistent right lower chest wall pain following 4 weeks of coryzal symptoms but denied fever or weight loss. She was being treated with ruxolitinib for myelofibrosis. C reactive protein was 9 mg/L. CT and MRI showed bilateral hilar and mediastinal lymphadenopathy, and lytic lesions in the T10 vertebral body and left iliac bone. Noncaseating granuloma were found on endobronchial ultrasound guided lymph node biopsy and on biopsy of the iliac crest, with sarcoid considered a possible diagnosis. Results On two occasions the patient had pain so severe that she required hospitalisation. Pulsed intravenous corticosteroids was given with symptomatic improvement. Iliac bone biopsy grew Mycobacterium Kansasii at 6-week culture. The patient completed 12 months of treatment (12 months rifampicin and isoniazid, 6 months ethambutol), with resulotion of pain. Conclusion We present a challenging case of mycobacterial osteomyelitis where there was initial diagnostic uncertainty. Sarcoidosis can involve multiple bony lesions but would not typically cause a spondylodiscitis. A recent pharmacovigilance report highlights that JAK inhibitors such as ruxolitinib increase the risk of mycobacterial infections, making specific investigations critical to diagnostic certainty.