TUBERCULOSIS: Overview of presentation (Canadian)

The clinical manifestations of pulmonary Tb are protean, but there are a few characteristic syndromes with which patients may present.
i) Primary Tb – The response to the first exposure to Tb, this is usually a subclinical process, though about 5% of immunocompetent patients will develop symtoms. Fever is the most common symptom, as relatively few patients actually have symptoms referable to the lungs (cough is the most common). Rarely, pleuritis or erythema nodosum may be seen. The most common CXR finding is hilar adenopathy, with or without infiltrates.
ii) Latent Tb – Most host’s will be able to control the initial exposure to Tb, rendering the organism dormant/latent. These patients are asymptomatic, and are diagnosed on the basis of a Tb skin test. Approximately 90% of these patients will remain latent; however, 5-10% will develop…iii) Reactivation Tb – If 10% of patients infected with Tb reactivate, 5% will do so within two years of initial infection, and 5% will do so beyond 2 years. Clinically, this is often a subacute or chronic process, with cough, fever, malaise and weight loss. Dyspnea and chest pain may develop, and the cough tends to become more productive over time. Other complications that are seen as the condition progresses include hemoptysis, effusions, bronchiectasis, and hematogenous dissemination (“miliary Tb”).CXR will typically reveal upper lobe infiltrates (reactivation Tb is most commonly found in the posterior apices). Cavitation and volume loss may also occur.
Note that 5% of patients with active Tb have a normal CXR.The gold standard for diagnosis of Tb is a positive culture for Mycobacterium tuberculosis.
Specimens for culture can be obtained via:- sputum (sensitivity approaches 90% with 3 acceptable samples)- induced sputum (sensitivity 90% when done correctly)- bronchoscopy (sensitivity 77%)- early morning gastric aspiration (sensitivity approx. 70%; uncomfortable and cumbersome)Prior to definitive culture results, public health will report the results of the acid-fast smear, and often results of nucleic acid amplification, ie. the (A)MTD test. The MTD is usually reserved for smear positive Tb, where it has high specificity, but sensitivity around 80%.
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