Mycobacterium microti pulmonary infection with vertebrodiscitis and a psoas abscess

Abstract

• Mycobacterium microti infection is not common. • This case illustrates an indolent and destructive infection. • Whole genome sequencing aided diagnosis. • A prolonged antibiotic course was required for clinical improvement and microbiological cure. Mycobacterium microti is a member of the Mycobacterium tuberculosis complex. It usually causes disease in various mammalian hosts, with its name being derived from rodents. It is difficult to process for sensitivities in the laboratory and clinical experience of this organism in human hosts is limited. We report a rare presentation of M. microti tuberculosis in a 40 year old female. She initially presented with palpitations and breathlessness. A chest X-ray was abnormal and subsequent Computed tomography (CT) of the chest and biopsy results led to a diagnosis of sarcoidosis. She was commenced on prednisolone and her breathing improved. Nine months later she developed back and leg pain with associated weakness. Spinal Magnetic Resonance Imaging (MRI) revealed vertebrodiscitis of L4/5 with an adjacent psoas abscess. Cultures from biopsies were negative. In the meantime her chest deteriorated and she became productive of green sputum. Three sputum samples were Acid-Fast Bacilli (AFB) smear positive and M. tuberculosis complex polymerase chain reaction (PCR) positive. Repeat chest X-ray showed bilateral upper lobe cavitation. It transpired that the patient lived in a rural area, close to fields and lakes. Her cat brought multiple dead rodents into the house, including voles. The patient was left to clear up their entrails. Sputum sample yielded M. microti . To our knowledge this is the first reported human instance of vertebrodiscitis and a psoas abscess due to M. microti . Although reportedly less pathogenic than M. tuberculosis , this case illustrates its indolent and tissue destructive potential and the need for prolonged courses of anti-tuberculous therapy.