Tenosynovitis Caused byMycobacterium arupensein a Patient with Diabetes Mellitus

To the Editor—Mycobacterium arupense, a slowly growing nonchromogenic mycobacterium, was first isolated from clinical samples in 2006 [1]. The clinical significance of this novel organism remains unknown. A 54-year-old woman presented with swelling and pain of the left middle finger and a tender nodule in the middle of her palm. Six months earlier, she had been involved in a motorcycle traffic accident and noted a mildly tender nodule on her left palm 1 month later. Swelling of the third distal phalanx then developed, and an incision was made on the palm after a diagnosis of trigger finger. The condition deteriorated after surgery, and a new nodule developed on the palm. She denied having contact with contaminated water or handling fish. Physical examination revealed diffuse swelling on the left middle finger and 2 tender nodules on the middle of her palm (figure 1). Tenosynovitis was suspected, and a biopsy was performed of a specimen obtained by incision. Pathological examination revealed suppurative granulomatous inflammation with Langhans giant cells, but results of acid-fast staining were negative. The lesions continued to progress despite empirical treatment, for 2 weeks, with minocycline (200 mg daily), itraconazole (400 mg daily), clarithromycin (1000 mg daily), rifampicin (450 mg daily), and ciprofloxacin (500 mg daily). Two months later, culture of a skin specimen grew acid-fast bacilli, and an unidentified Mycobacterium species was reported with test results. Because of the deterioration of the patient's clinical condition, synovectomy and debridement were performed. The patient then received treatment with clarithromycin (500 mg every 12 h), moxifloxacin (400 mg daily), rifabutin (300 mg daily), ciprofloxacin (400 mg every 12 h), and ethambutol (1000 mg daily) for 6 months, and her condition improved. Diffuse swelling on the left middle finger and 2 tender nodules (arrows) on the middle of the palm of a patient with tenosynovitis caused by Mycobacterium arupense. The isolate was negative for niacin accumulation and was positive for catalase under the following conditions: 68°C, hydrolysis of Tween 80, and arylsulfatase at 14 days. The partial sequence (850 nucleotides) was compared with published sequences in the GenBank database of the National Center for Biotechnology Information with the BLAST algorithm. The closest match was obtained with M. arupense (GenBank accession number AB239927.1) with 99% identity [1]. Cases of tenosynovitis caused by nontuberculous mycobacteria have been reported elsewhere [2–5]. Three isolates of M. arupense recovered from clinical specimens have been described in the literature [1, 6]. Two of these isolates were from patients with tenosynovitis, and another isolate was recovered from the sputum of a patient with an abnormal chest radiograph [1, 6]. M. arupense has also been isolated from fish tank water samples [7]. This organism was characterized on the basis of 16S ribosomal RNA, hsp65, and ropB and some specific phenotypic characteristics that were subsequently demonstrated to be variable among strains [1, 6]. Optimal therapy for M. arupense infection has not been established. The limited data available on antimicrobial susceptibility indicated that clarithromycin (MIC, <0.03 µg/mL), amikacin (MIC, <0.5 µg/mL), streptomycin (MIC, 0.25–0.5 µg/mL), ethambutol (MIC, 0.5–1 µg/mL) had good in vitro activity against M. arupense [1, 6]. Variable in vitro activities were found for rifampin (MIC, 0.12–8 µg/mL) or rifabutin and levofloxacin (MIC, 0.25–4 µg/mL). Isoniazid (MIC, >32 µg/mL) had the poorest activity [1]. In conclusion, we describe a case of tenosynovitis caused by M. arupense in a patient with diabetes mellitus. Because of the diversity of Mycobacterium species, accurate identification is imperative before proper treatment can be determined. Further research is needed to reveal the clinical spectrum of human infection caused by M. arupense. Potential conflicts of interest. All authors: no conflicts.