Insulin Injection Abscesses Caused by Mycobacterium Chelonae

Insulin injection abscesses occur in patients with diabetes and are mainly due to Staphylococcus aureus. However, we need to look for other organisms that can cause problems so that appropriate treatment can be given. Here we report a case of injection abscesses due to an atypical mycobacterium, Mycobacterium chelonae.

A 43-year-old woman with diabetes presented with a 5-month history of abscesses on her thighs and abdomen at injection sites. She used a pen device three times daily (reusing the needle) and a syringe and needle in the evening. With an HbA_1c of 14%, her diabetes control was far from ideal. She had a 23-year history of diabetes and had been admitted to the hospital on a few occasions for seizures during episodes of hypoglycemia.

The abscesses had been treated with several courses of oral flucloxacillin but continued to enlarge with the development of new lesions. The largest abscess on her right thigh was incised and drained by the general surgeons and continued to drain pus after the procedure. No infecting organism had been isolated from charcoal swabs of the lesions.

On presentation, she had a large abscess draining pus on the left thigh with smaller nodules on the right thigh and a carbuncle on her anterior abdominal wall. She was well, apyrexial, and her diabetes control had not changed significantly since the abscesses had appeared.

After discussion with the microbiology department with reference to the obvious pus but apparently sterile culture taken from the swabs, pus was aspirated from the abscess on the thigh and sent for culture. A skin biopsy was also taken and sent for histological assessment and culture. The biopsy showed a deep dermal abscess with inflammation. Microscopy of the pus did not show acid and alcohol fast bacilli (AFBs). After being cultured for 6 weeks at 30°C, M. chelonae was isolated from the pus. This was sent to the reference laboratory where the diagnosis was confirmed and the M. chelonae was found to be sensitive to clarithromycin and ciprofloxacin. The cultures of the patient’s needles and pen device did not reveal any M. chelonae.

The patient was started on 500 mg b.d. clarithromycin and 250 mg t.d.s. ciprofloxacin, which cleared the abscesses over the next few months. Toward the end of treatment a new nodule appeared on the right thigh away from injection sites, which was completely excised. The histology showed granulomatous inflammation in the deep dermis and subcutis. A single well-formed AFB was identified by a modified Zeil-Neilsen stain. Treatment was continued for 6 months after the lesions cleared, and the patient has remained well and has not developed any new lesions.

M. chelonae is a fast-growing, atypical mycobacterium of Runyon group IV. It is considered fast growing as it grows in 3–7 days at 25°C to 40°C compared with other groups that require 2 weeks to grow. Despite this, M. chelonae is difficult to culture.

It is widespread in the environment and has been reported to survive on the skin for 6 h. It is contracted from the environment rather than by human-to-human transmission but rarely causes human disease. Primary cutaneous infections have been reported after injections in patients with diabetes on insulin (2,3) and in postoperative patients. In immunocompetent patients there is usually a known portal of entry, but cutaneous disease can follow dissemination from an endogenous source (4). Disseminated disease is more likely to occur in immunosuppressed patients, such as those on long term steroids or after a renal transplant (5). In a study of 100 cases of cutaneous disease, 35% had localized infections following trauma and, of these, 3 had diabetes (6)

The presentation of cutaneous infection includes localized cellulitis, granulomatous nodules, abscesses, and ulcers (7). Lesions have been noted to exhibit spirotrichoid spread (8). This is lymphangitic spread with nodules ascending proximally along lymphatic vessels. Extracutaneous lesions include osteomyelitis, endocarditis, and keratitis following surgery and may be related to catheters, renal dialysis catheters, and tracheostomy tubes.

M. chelonae is resistant to usual antituberculous treatment but may be sensitive to clarithromycin and ciprofloxacin. It may also respond to imipenem and linezolid. This case reinforces the need to consider atypical infections in cases of persistant cutaneous infection, especially in patients who are relatively immunocompromised.