Armando Hasudungan
Biology and Medicine videos

Tuberculosis

Overview

Definitions
Latent Tuberculosis: Asymptomatic infection of Mycobacterium tuberculosis.
Primary Tuberculosis: Development of clinical illness immediately after infection with M tuberculosis.
Reactivation Tuberculosis: Illness that occurs when latent TB becomes active and infectious after a period of dormancy, such as years after the initial infection.

Often seen in children, primary pulmonary TB usually affects the middle and lower lung zones. Lesions form in the periphery with hilar and paratracheal lymphadenopathy. Granulomatous lesions are caused by the inflammatory response of lymphocytes and macrophages. The center of the lesion may become necrotic (caseous necrosis) and liquefied, forming a cavity. Healed lesions are called Ghon lesions.

Reactivation TB usually involves the apical and posterior segments of the upper lobes or the superior segments of the lower lobes of the lungs. The course may be rapid (weeks to months), chronic and slowly progressive (“consumption”), or spontaneously remit.

Investigation

The diagnosis of TB is made by combining the history and clinical picture with AFB stains or culture of a specimen (smear or tissue biopsy).

Purified protein derivative (PPD), or tuberculin, skin testing is useful for screening for latent TB infection but has a limited role in diagnosing active infection because of frequent false-negative results in this setting. A positive PPD is defined by induration of at least 5 mm after 48 to 72 hours

Management

Individuals with active tuberculosis should be initiated on multidrug therapy, such as isoniazid, rifampin, pyrazinamide, and ethambutol. Pyridoxine (vitamin B6 ) is usually added to antituberculosis medications to prevent peripheral neuropathy.