Mycobacterium abscessus (M. abscessus) belongs to the M. chelonae/abscessus complex and the rapid growth group of nontuberculous mycobacteria. Tender nodules, ulcers, and abscesses may occur during skin infection. This case reports a nontraumatic M. abscessus skin infection in a healthy adult.

A 41-year-old female patient with no specific medical or traumatic history visited our hospital with a skin lesion on the right calf that had developed 3 months earlier. Although incision and drainage were performed twice and the patient was treated with oral antibiotics in another hospital, no improvement was realized. A rigid patch approximately 2 cm in diameter was observed on the right calf, which was accom- panied by slight skin depression, erythema, abscess, and tenderness (Fig. 1A). On the first visit, no symptoms other than the lesion were observed and no abnormalities were found in the blood test, fungus study, or chest X-ray. Histo- logical examination revealed an abscess containing neutro- phils on the upper dermis layer and chronic granulomatous inflammation, including Langhans giant cells, on the deep dermal and subcutaneous fat layers. Mycobacteria staining showed a positive result (Fig. 1B). The combination of anti- tuberculosis drugs for three weeks showed no improvement. Therefore, nontuberculous mycobacterium (NTM) polymerase chain reaction (PCR) and culture were performed. To dis- tinguish M. abscessus and M. massiliense, the erythromycin ribosome methyltransferase (erm) gene was confirmed using an ERM-plus real-time PCR kit (LG Chem; not a commercial product)¹, and M. abscessus was detected. The antibiotic susceptibility test was sensitive to amikacin, clarithromycin, imipenem, and linezolid. We started treatment with 500-mg oral clarithromycin twice a day and 500-mg levofloxacin once a day. After 24 weeks of treatment, all lesions improved without recurrence.

Figure 1. (A) Solitary dimpled erythematous patch on the right shin approximately 2 cm in diameter (B) Purplish-stained acid-fast bacilli are seen (Ziehl-Neelsen stain, ×400).

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M. abscessus is found in soil, water, and dust. In addition to skin diseases, it can infect joints, bones, and lungs. In Korea, trauma-related skin infections, such as mesotherapy, have been reported. However, only a few nontraumatic cases have been reported in healthy people^3-5. M. abscessus infection is mainly caused by invasive actions, such as injections, surgery, or trauma. However, in this case, the M. abscessus infection occurred in a healthy adult without a history of invasive procedures or trauma.

Currently, no standard guidelines exist for treating cuta-neous M. abscessus infections. M. abscessus is generally sen- sitive to macrolides, such as clarithromycin and azithromycin, but may have resistance genes, such as erm41. Therefore, combination therapy with other antibiotics is recommended². In cases of M. abscessus without trauma in a healthy adult in Korea, combination antibiotic therapy is used. The treatment period varies from 2 to 6 months, and in one case, incision and drainage were additionally performed (Table 1).

If subcutaneous nodules do not improve with conventional treatment, mycobacterial infection should be suspected. In the case of M. abscessus infection, an antibiotic susceptibility test and antibiotic combination therapy based on clarithro- mycin should be implemented for 4~6 months.