A Surprising Case of Mycobacterium Avium Complex Skin Infection in an Immunocompetent Patient

December 2014 | Volume 13 | Issue 12 | Case Report | 1491 | Copyright © 2014

Angelo Landriscina BA,a Tagai Musaev BA,a Bijal Amin MD,b and Adam J. Friedman MDa,c

aDepartment of Medicine (Division of Dermatology), Albert Einstein College of Medicine, Bronx, NY
bDepartment of Pathology, Montefiore Medical Center, Bronx, NY
cDepartment of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY


An acute inflammatory nodule of unknown etiology can pose a formidable diagnostic challenge. Here, we highlight the importance of including Mycobacterium avium intracellulare complex (MAC) and other atypical mycobacterial infections in the differential diagnosis of a cutaneous nodule in an immunocompetent individual. We also explore the implications of eczema in the development of a mycobacterial infectious process. We report a case of MAC skin infection in an immunocompetent individual. The patient is a 49-year-old male with a history of dyshidrotic eczema presenting with a fluctuant, non-draining nodule on his right forearm for 2 to 3 weeks, identified by tissue DNA probe to be a cutaneous MAC infection without systemic complications, as serologies and chest X-ray were unremarkable. MAC should be included in the broader differential diagnosis of deep fungal vs atypical mycobacterial skin infections. Nucleic acid-based assays are an important tool in making a definitive diagnosis, allowing for utilization of appropriate therapy for the specific etiologic pathogen. Given the patient’s preceding diagnosis of eczema, it is possible that the compromised skin barrier and dampened cytotoxic Th1 activity predisposed the patient to this infection, typically appreciated in the immunosuppressed, warranting further investigation into the relative risk for atypical mycobacterial infections in the setting of eczema.

J Drugs Dermatol. 2014;13(12):1491-1493.

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Mycobacterium avium intracellulare complex (MAC) includes 2 genetically similar organisms: Mycobacterium avium and Mycobacterium intracellulare. MAC species are widely found in the environment, and are a major cause of nontuberculous mycobacterial infections worldwide.1 Although MAC is ubiquitous, it mainly causes disease in immunocompromised individuals. While rare, there are reports of varied cutaneous phenotypes including pustules, plaques or nodules.2,3 Here we present a notable case of a MAC skin infection in an immunocompetent patient without disseminated disease.


A 49-year-old male physician assistant, with a past medical history significant for dyshidrotic eczema, presented with a 2 to 3 week history of a tender, fluctuant nodule of the right forearm. The patient noted that he had visited Arizona prior to the development of the nodule and initially believed it to be caused by an arthropod bite. A 10-day course of trimethoprimsulfamethoxazole, which was prescribed by another provider, failed to alleviate his symptoms. Review of systems revealed no other pertinent findings.

A physical exam was notable for an ovoid, fluctuant, erythematous, tender dermal nodule on the right forearm. The remainder of the exam was unremarkable. Two punch biopsies of the lesion were collected and sent for pathology and tissue culture. Biopsy sites expressed no purulent material.

The histology demonstrated epidermal hyperplasia and hyperkeratosis as well as perivascular and perifollicular inflammatory cell infiltrate at low power. At high power, a perivascular inflammatory cell infiltrate was seen containing lymphocytes, histiocytes, and occasional eosinophils and neutrophils. A PAS-D stain, Gram stain, and Fite stain were negative for fungi, bacteria, and acid-fast bacilli, respectively.

Tissue culture and culture for acid-fast bacilli were unremarkable. A DNA probe was positive for MAC.

A diagnosis of atypical mycobacterial skin infection was made following a normal complete blood count, negative HIV test, and chest X-ray. A 9-month course of rifampin and clarithromycin was prescribed. Follow-up at 1, 2, and 5 months showed significant improvement in the lesion with decreased size, tenderness, and erythema.


Mycobacterium avium intracellulare complex is a group of genetically similar mycobacterial species best known for causing pulmonary infections in immunocompromised patients. MAC is ubiquitous in the environment, and the most common

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