Approach
Clinical presentation of Mycobacterium avium complex (MAC) varies according to the site of infection and patient characteristics. Diagnosis may be confirmed by radiologic techniques and microbiologic sampling (sputum or blood). More invasive procedures such as biopsy and bone marrow aspirate may be necessary in specific cases.
Pulmonary MAC
Symptoms corroborative of MAC lung disease are cough, fatigue, fever, and weight loss, especially in those with underlying lung diseases for whom an alternative diagnosis has not been obtained and treatment with conventional antibiotics has not been successful.[30]
One form of pulmonary MAC disease presents as a subacute to chronic illness with productive cough, weight loss, fever, or night sweats in middle-aged-to-older men, frequently with a history of underlying lung disease, heavy smoking, and excessive alcohol consumption.
The second form presents with a more indolent clinical picture in middle-aged-to-older women with no preexisting lung disease. These patients have chronic cough but no constitutional symptoms such as fever or weight loss. The characteristic morphotype is a thin body habitus with scoliosis and pectus excavatum. Also, commonly associated with mitral valve prolapse.
Patients with the above symptoms should have a chest x-ray performed, with comparison to old films if available. The presence of infiltrates (with or without nodules), multiple nodules, or cavitations suggest MAC.
An abnormal chest x-ray but without cavitations should prompt high-resolution computed tomography (HRCT) scanning. This may show multiple small nodules and multifocal bronchiectasis with or without lung nodules.
When clinical and radiologic findings suggest the diagnosis, microbiologic analysis of sputum is required.
Bronchoscopy, lung biopsy, and bronchial lavage are performed when sputum cultures are nondiagnostic.
Disseminated MAC
History of HIV infection or general severe immune suppression, leukemia, lymphoma, organ transplantation, or other immunosuppressive therapy. Present with a febrile illness with fever, fatigue, abdominal pain, and diarrhea.[18] Hepatomegaly and/or splenomegaly may be present on physical exam.
Blood testing with complete blood count, liver function test, and culture should be performed initially. Culture positive with 1+ growth is sufficient if HIV-positive with CD4 under 200 cells/microliter.[30] Bone marrow aspirate and culture are useful in HIV-associated MAC disease and may yield a quicker result.
Polymerase chain reaction of blood is a promising test for MAC detection, but is not yet not available for routine clinical use.[32]
Cervical lymphadenitis
Occurs predominantly in children with the majority of cases occurring between 1 and 5 years of age. It has a subacute or chronic course with cervicofacial lymph node enlargement and can be associated with constitutional symptoms or fever.[33][34] It is usually unilateral. Potential complications of the disease include extranodal extension and sinus tract formation.[35]
Lymph node biopsy should be performed and will reveal granulomas and culture MAC.
Hypersensitivity pneumonitis
A form of hypersensitivity pneumonitis associated with hot tub use and attributed to infection with MAC commonly referred to as ‘'hot tub lung'’. The most common symptoms are cough and dyspnea, which develop in temporal relationship to hot tub use.[36] Symptoms may be accompanied by fevers.
A chest x-ray should be performed initially, with subsequent HRCT if chest x-ray suggests interstitial or micronodular infiltrates. HRCT shows diffuse centrilobular nodules and/or ground-glass infiltrates.
Cultures of sputum and hot tub water samples are recommended.
Bronchoscopy, lung biopsy, and bronchial lavage are performed when sputum cultures are nondiagnostic. Histology shows noncaseating granulomas.[37]
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