Atypical Osteomyelitis Caused by Mycobacterium chelonae—A Multimodal Imaging Approach

We present an unusual case of a biopsy-proven Mycobacterium chelonae infection (MCI) of skin and soft tissue, which led to osteomyelitis in a 55-year-old Caucasian male. We provide clinical data and discussion about MCI and its diagnostic workup and demonstrate comprehensive imaging findings, including clinical pictures, radiographs, three-phase bone scintigraphy, and combined SPECT/CT findings of this entity, which have not yet been presented in the medical literature. 1. Introduction Mycobacterium chelonae is an atypical mycobacterium which does not cause tuberculosis or leprosy in humans. They are known for infections of skin, lungs, eyes, and soft tissue. People with immunodeficiency are more likely to contract an infection although a minority of concerned patients were reported to be primary healthy. The identification of the agent is performed by bacterial cultures, polymerase chain reaction (PCR), and DNA sequencing [1]. Bone and joint infections are extremely rare in the context of atypical mycobacterium infections [2]. Osteomyelitis is mostly caused by staphylococcus aureus (75–80%), infrequently also by other bacteria, viruses, and funguses [2, 3]. In the medical literature we found only 2 cases of Mycobacterium chelonae osteomyelitis visualized by multiple diagnostic imaging modalities [2, 4]. To our best knowledge SPECT/CT findings have not yet been published at all. 2. Clinical Presentation The patient is a 55-year-old Caucasian male with an unclear redness and swelling at the right medial malleolus without any noticed trauma. His medical record includes ulcerative colitis and sarcoidosis treated with prolonged cortisone therapy and liver transplant for treatment of primary sclerosing cholangitis (PSC) 14 years ago. Tentative diagnosis was gout because of high uric acid in blood testing but common ambulant drug therapy with colchicine and indomethacin did not improve the condition. Spreading of the swelling and redness in combination with increasing inflammation parameters was interpreted as possible phlegmon and treated with penicillin. However no regression was observed and the patient developed additional nodular lesions spreading from the ankle to the anterior medial lower leg. Visible were 12–15 nodular lesions, the newest and proximal lesions were erythematous, and the older ones were darker and violaceous with some scaling (Figure 1). Figure 1: Clinical picture shows swelling and erythema over the medial aspect of the right ankle. In addition nodular lesions on the lower leg are seen. In the following, punch biopsies were performed,