Tuberculosis
An acute or chronic infection, tuberculosis is characterized by pulmonary infiltrates and by formation of granulomas with caseation, fibrosis, and cavitation. The American Lung Association estimates that active disease has increased by more than 20% in the past 5 years.
The disease is twice as common in males as in females and four times as common in nonwhites as in whites. But incidence is highest in people who live in crowded, poorly ventilated, unsanitary conditions, such as those in some prisons, tenement houses, and homeless shelters. The typical newly diagnosed tuberculosis patient is a single, homeless, nonwhite
male. With proper treatment, the prognosis is usually excellent. (See Who’s at risk for tuberculosis?)
male. With proper treatment, the prognosis is usually excellent. (See Who’s at risk for tuberculosis?)
Causes
Tuberculosis results from exposure to Mycobacterium tuberculosis or other strains of mycobacteria. Transmission occurs when an infected person coughs or sneezes, spreading infected droplets.
When a person without immunity inhales these droplets, the bacilli lodge in the alveoli, causing irritation. The immune system responds by sending leukocytes, lymphocytes, and macrophages to surround the bacilli, and the local lymph nodes swell and become inflamed. If the encapsulated bacilli (tubercles) and the inflamed nodes rupture, the infection contaminates the surrounding tissue and may spread through the blood and lymphatic circulation to distant sites—a process called hematogenous dissemination. This same phagocytic cycle occurs whenever the bacilli spread.
After exposure to M. tuberculosis, roughly 5% of infected people develop active tuberculosis within 1 year; in the remainder, microorganisms cause a latent infection. The host’s immunologic defense system usually destroys the bacillus or walls it up in a tubercle. But the live, encapsulated bacilli may lie dormant within the tubercle for years, reactivating later to cause active infection.
Complications
Tuberculosis can cause massive pulmonary tissue damage, with inflammation and tissue necrosis eventually leading to respiratory failure. Bronchopleural fistulas can develop from lung tissue damage, resulting in pneumothorax. The disease can also lead to hemorrhage, pleural effusion, and pneumonia. Small mycobacterial foci can infect other body organs, including the kidneys and the central nervous and skeletal systems.
Assessment
The patient with a primary infection may complain of weakness and fatigue, anorexia and weight loss, and night sweats. The patient with reactivated tuberculosis may report chest pain and a cough that produces blood or mucopurulent or blood-tinged sputum. He may also have a low-grade fever.
Who’s at risk for tuberculosis?
The risk of tuberculosis is higher in the following groups:
Black and Hispanic men between ages 25 and 44
those in close contact with a patient whose tuberculosis is newly diagnosed
those who have had tuberculosis before
people who have had multiple sexual partners
recent immigrants from Africa, Asia, Mexico, and South America
patients who have had gastrectomy
people affected with silicosis, diabetes, malnutrition, cancer, Hodgkin’s disease, or leukemia
those who abuse alcohol or drugs
patients in mental institutions
residents of nursing homes (10 times more likely to contract tuberculosis than people in the general population)
those receiving immunosuppressants or corticosteroids
people with weak immune systems or diseases that affect the immune system, especially those with acquired immunodeficiency syndrome.
When you percuss, you may note dullness over the affected area, a sign of consolidation or the presence of pleural fluid. On auscultation, you may hear crepitant crackles, bronchial breath sounds, wheezes, and whispered pectoriloquy.
Diagnostic tests
Chest X-rays show nodular lesions, patchy infiltrates (mainly in upper lobes), cavity formation, scar tissue, and calcium deposits. However, they may not help distinguish between active and inactive tuberculosis.
A tuberculin skin test reveals that the patient has been infected with tuberculosis
at some point, but it doesn’t indicate active disease. In this test, intermediate-strength purified protein derivative or 5 tuberculin units (0.1 ml) are injected intradermally on the forearm and read in 48 to 72 hours. A positive reaction (equal to or more than a 10-mm induration) develops within 2 to 10 weeks after infection with the tubercle bacillus in both active and inactive tuberculosis.
Stains and cultures—of sputum, cerebrospinal fluid, urine, drainage from abscess, or pleural fluid—show heat-sensitive, nonmotile, aerobic, acid-fast bacilli.
Computed tomography or magnetic resonance imaging scans allow the evaluation of lung damage or confirm a difficult diagnosis.
Bronchoscopy may be performed if the patient can’t produce an adequate sputum specimen.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
