A 75 y/o woman with SLE on 10mg daily prednisone and hydroxychloroquine was hospitalized due to hyponatremia and 6 month history of chronic, intermittent lower back pain acutely worsening several days prior to admission. 1 month of almost daily subjective fevers and weight loss. History of initially necrotic, 1 cm wound on her right calf developing five months prior to admission described as “brown recluse spider bite” which formed a chronic non-healing leg ulcer. Outpatient MRI, biopsy and aerobic culture of the ulcer were non-diagnostic. She had no history of trauma, spinal injections, or past cardiac surgery. Initially afebrile with normal vital signs and exam only positive for mild lumbar tenderness. Initial testing notable for hyponatremia with a sodium of 124 mmol/L, ESR 106 mm/hr, and CRP 117 mg/L. WBC 5.4 x 109/L, HB 11.6 g/dL, and PLT 175 109/L. HIV negative and quantiferon indeterminate. MRI revealed multilevel discitis at L5-S1, L2-3, and T8-9 with prevertebral osteomyelitis, and a paraspinal abscess at L5-S1. Percutaneous aspiration of abscess returned rare PMNs without organisms on conventional or AFB staining. On day 12, M. chimaera was identified from aspirate culture. New biopsy culture of the calf wound returned positive for the same organism.
Discussion:
In Greek mythology, the chimera is a fearsome creature containing the heads of a lion, goat, and snake. M. chimaera represents a biofilm-forming non-tuberculous mycobacteria (NTM) newly identified in 2004. Non-sequencing methods used to identify Mycobacterium spp. may fail to identify M. chimaera and some infections previously attributed to M. avium and M. intracellulare are now known to be M. chimaera. Disseminated infection with M. chimaera has been described following cardiac surgery, vascular graft infection, prosthetic valve endocarditis, or myocarditis. Outbreaks of M. chimaera have occurred from contamination of heart-lung bypass machines. M. chimaera can also cause pulmonary infection, similar to the other MAC species. Unlike prior descriptions of patients with M. chimaera, our patient did not have a history of trauma or cardiac surgery and this is the first description of M. chimaera osteomyelitis absent these risk factors. Her chronic immunosuppression was a likely predisposing factor. The patient in this case presented with a history of chronic non-healing leg wound months prior to admission. Given that the leg wound later grew AFB, her ulcer was likely the first manifestation of the disease, months before diagnosis of spinal involvement. Like the other MAC species, M. Chimera is typically treated with a prolonged course of clarythromicin, ethambutol, and rifampin. Vertebral osteomyelitis often requires surgery.
Conclusions:
This case emphasizes the importance of considering slow-growing NTM species in the evaluation of non-healing wounds in immune compromised patients. Conventional pathology and bacterial cultures may fail to make a timely diagnosis.