Case Letter

Mycobacterium haemophilum: A Challenging Treatment Dilemma in an Immunocompromised Patient

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The patient was evaluated by the dermatology consultation service on hospital day 1. At the time of consultation, the lesions were still painless but had enlarged. Two new satellite lesions were noted on his other extremities. Due to the widespread distribution of the lesions, there was concern for disseminated disease. The relatively rapid onset of new lesions increased concern for infection with rapid-growing mycobacteria, including Mycobacterium abscessus, Mycobacterium fortuitum, and Mycobacterium chelonae. A detailed history revealed that the patient’s wife had a fish tank, which supported the inclusion of Mycobacterium marinum in the differential; however, further questioning revealed that the patient never came in contact with the aquarium water. The initial outpatient biopsy had not been sent for culture. Following inpatient biopsy, the patient was initiated on empiric antimycobacterials, including imipenem, amikacin, clarithromycin, and levofloxacin. Computed tomography of the head was negative for cerebral involvement.

Acid-fast bacilli blood cultures were drawn per the recommendation from infectious diseases in an attempt to confirm disseminated disease; however, blood cultures remained negative. Tissue biopsy from the right arm was sent for AFB staining and culture. Many AFB were identified on microscopy, and growth was observed in the mycobacterial growth indicator tube after 6 days of incubation. The DNA probe was negative for M tuberculosis complex or Mycobacterium avium complex.

The patient was discharged on hospital day 6 on empiric therapy for rapid-growing mycobacteria while cultures were pending. The empiric regimen included intravenous imipenem 1 g every 6 hours, intravenous amikacin 1 g once daily, clarithromycin 500 mg every 12 hours, and levofloxacin 750 mg once daily. All solid media cultures were negative at the time of discharge.

The biopsy specimen proved difficult to culture on solid media using traditional methods. Three weeks after the inpatient biopsy, the microbiology laboratory reported that growth was observed on solid media that was incubated at 30°C and supplemented with iron. These findings were not characteristic of a rapidly growing mycobacteria (eg, M fortuitum, M chelonae, M abscessus) or M marinum but raised concern for infectionwith M haemophilum. Antimycobacterial treatment was adjusted to amikacin, clarithromycin, levofloxacin, and rifabutin.

Six weeks after the inpatient skin biopsy, final speciation confirmed infection with M haemophilum. The isolate proved susceptible to amikacin (minimal inhibitory concentration [MIC], 16), clarithromycin (MIC, 0.12), linezolid (MIC, <1), moxifloxacin (MIC, 0.5), rifabutin (MIC, <0.25), and trimethoprim-sulfamethoxazole (MIC, 0.5/9.5). The isolate was resistant to ciprofloxacin (MIC, 4), ethambutol (MIC, >16), and rifampin (MIC, 2). Based on these findings, an infectious disease specialist modified the treatment regimen to azithromycin 600 mg once daily, moxifloxacin 400 mg once daily, and rifabutin 300 mg once daily. Azithromycin was substituted for clarithromycin in an attempt to minimize the gastrointestinal side effects of the antibiotics. The infectious disease specialist was concerned that the clarithromycin could exacerbate the patient’s chronic GVHD-associated diarrhea, which posed a challenge to the oncologist, who was attempting to manage the patient’s GVHD and minimize the use of additional prednisone. At the time of this change, the patient was doing well clinically and denied any active skin lesions.

Four months later, he developed new left-sided neck swelling. Computed tomography revealed nonspecific enhancement involving the skin and superficial subcutaneous tissues in the left anterior neck. He was referred to otolaryngology given concern for recurrent infection vs leukemia cutis. He underwent excisional biopsy. Pathology was negative for malignancy but demonstrated subcutaneous necrotizing granulomatous inflammation with a positive AFB stain. Tissue AFB cultures revealed moderate AFB on direct stain, but there was no AFB growth at 12 weeks. Clarithromycin was restarted in place of azithromycin to increase the potency of the antimycobacterial regimen. Cultures from this neck biopsy were negative after 12 weeks of incubation.

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