Differentials
Pulmonary tuberculosis
SIGNS / SYMPTOMS
Difficult to clinically distinguish tuberculosis from Mycobacterium avium complex (MAC).
History of tuberculosis exposure is helpful though not diagnostic.
INVESTIGATIONS
Difficult to distinguish MAC fibrocavitary lesions from tuberculosis on lung imaging. However, MAC tends to have thinner-walled cavities, more contiguous extension of disease, and more pleural involvement.
Smears will not distinguish between types of mycobacteria.
Cultures are necessary to determine type.
Other nontuberculous mycobacteria (NTM)
SIGNS / SYMPTOMS
Other types of NTM, such as M fortuitum or M cheloneae/abscessus, are difficult to distinguish based on symptoms.
INVESTIGATIONS
Smears will not distinguish mycobacteria.
Cultures are the most accurate way of making the distinction.
HIV-related lymphoma
SIGNS / SYMPTOMS
Clinically difficult to distinguish from disseminated Mycobacterium avium complex (MAC).
INVESTIGATIONS
Histopathology is required to make the diagnosis of lymphoma.
Cultures will be negative unless superimposed MAC infection present.
Histoplasmosis
SIGNS / SYMPTOMS
Fungal infection commonly seen in immunosuppressed patients.
Clinically difficult to distinguish from Mycobacterium avium complex.
INVESTIGATIONS
Chest x-ray shows solitary pulmonary nodule that rarely cavitates.
Diagnosed by culture, fungal stains, serologic tests for antibodies, and antigen detection.
Blastomycosis
SIGNS / SYMPTOMS
Fungal infection with similar clinical presentation to Mycobacterium avium complex.
Commonly associated with skin lesions such as widespread papules or erythematous verrucous lesions.
INVESTIGATIONS
Chest x-ray may have abnormal infiltrates.
Sputum smear with fungal stains may show organism.
Culture of sputum positive for fungus.
Skin biopsy of lesion may show organism.
Cryptococcosis
SIGNS / SYMPTOMS
Causes pulmonary, neurologic and disseminated disease.
Pedunculated skin lesions.
Central nervous system manifestations do not rule out disseminated Mycobacterium avium complex but are more suggestive of cryptococcosis.
INVESTIGATIONS
Peripheral and cerebrospinal fluid cryptococcal antigen are very sensitive and specific tests.
Wasting syndrome
SIGNS / SYMPTOMS
Occurs in people with HIV in the absence of opportunistic infections or other identifiable causes of weight loss.
INVESTIGATIONS
Clinical diagnosis of exclusion.
Sarcoidosis
SIGNS / SYMPTOMS
Difficult to differentiate from pulmonary Mycobacterium avium complex and hypersensitivity pneumonitis.
INVESTIGATIONS
Bilateral hilar lymphadenopathy on chest x-ray; lung biopsy demonstrates granulomatous tissue.
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