Rapidly growing atypical mycobacteria are non-motile, aerobic bacteria that are ubiquitous in both natural and nosocomial environments1. While the prevalence of these organisms is not well described2, they have become an increasingly common source of localized skin and soft tissue infections, particularly in immunocompromised patients. Despite its ever-growing presence, this bacterium is difficult to identify due to late presentation of symptoms and negative results from conventional bacterial cultures and gram stains3. Mycobacterium mageritense, a non-pigmented rapidly growing atypical mycobacteria4, is an example of a newly isolated source of cutaneous infections that is difficult to identify in laboratories. Repeat cultures from direct biopsy samples, supplemented by histopathological investigation are recommended for the most accurate diagnosis3. In addition to acid fast staining, “laboratories should hold on to routine bacterial cultures for a minimum of three days to ensure the recovery of these organisms”4. Due to the increasing prevalence of these infections, awareness of proper diagnostic technique is critical in effective treatment planning. Physicians should have a higher degree of suspicion for rapidly growing atypical mycobacteria, including Mycobacterium mageritense, in immunocompromised patients with abscess of unknown etiology.

Case Presentation:

A 50 year-old woman with a past medical history of breast cancer presented to a chemotherapy session with a progressively worsening circular skin nodule on her right upper extremity over the last week. She complained of a warm, erythematous, fluctuant, 1.5 by 2 centimeter nodule on the lateral aspect of her right forearm. It had a central ulceration with mild overlying scale without any purulent drainage. There was no erythematous streaking towards the axilla or along the forearm distal to the lesion or palpable lymphadenopathy. She also endorsed intermittent fevers up to 103 degrees Fahrenheit but was generally nontoxic appearing upon presentation. Notably, the patient underwent right-sided modified radical mastectomy five months prior to presentation and had been actively receiving intravenous adjuvant chemotherapy via chest wall Metaport. Her oncologic course was uncomplicated and she had not been recently hospitalized.