Background: Nontuberculous mycobacteria (NTM) are abundant in soil and water. They can cause infection by direct inoculation via even minimal trauma. Chronic soft tissue infection may extend to involve joints and underlying bone by direct extension. Septic joint infections due to NTM are rare and much of what is known about their management is either taken from case reports or extrapolated from the tuberculosis literature.

Methods: Here we describe a case of septic ankle due to M. chelonae, a rapidly growing NTM. We also review the literature of mycobacterial infection, prognosis, and the treatment pharmacology of these difficult to treat infections.

Results: An 86-year-old man presented to our hospital with complaints of a painful, swollen, left ankle. Three months earlier he had seen a pimple on his left foot after tripping over a lawn mower. The lesion evolved into erythema and swelling of the left ankle which was so painful that he could not bear weight on his left lower extremity (LLE). MRI of the LLE revealed a comminuted nondisplaced fracture of the distal tibial metaphysis. Turbid joint fluid was aspirated, and cell studies showed 211,450 k/uL white blood cells with 97% neutrophils. Patient underwent partial removal of the left tibia with insertion of a drug implant device. Tissue culture grew acid fast bacilli. Histopathology also showed acid-fast bacilli, confirming an atypical mycobacterial infection. Meropenem, linezolid, and azithromycin were initiated until the organism was identified as Mycobacterium chelonae. Based on susceptibility report, meropenem was discontinued, and ciprofloxacin was initiated. After discharge, a repeat MRI showed possible osteomyelitis and small abscesses about the left ankle. This prompted a repeat debridement. Tobramycin was started and ciprofloxacin was discontinued. The patient was re-admitted shortly after discharge with acute renal failure and lactic acidosis; he ultimately passed away on comfort care per patient and family wishes.

Conclusion: NTM are more resistant to antimycobacterial therapy compared with mycobacteria tuberculosis (MTb) and repeat surgical debridement is often necessary for cure. Because these cases are rare, it is important to approach treatment as a team including ID physicians, ID pharmacists, and surgeons to improve outcomes.