Tuberculosis

Tuberculosis (TB) is an acute or chronic infection characterized by pulmonary infiltrates and by the 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 men as in women and four times as common in nonwhites as in whites. Incidence is highest in people who live in crowded, poorly ventilated, unsanitary conditions, such as prisons, tenement houses, and homeless shelters. The typical newly diagnosed patient with TB is a single, homeless, nonwhite man. With proper treatment, the prognosis is usually excellent.

Causes

TB results from exposure to Mycobacterium tuberculosis and, sometimes, other strains of mycobacteria. Transmission occurs when an infected person coughs or sneezes, spreading infected droplets.

The following are at-risk populations that incur a high incidence of TB with presenting symptoms:

• Black and Hispanic men between ages 25 and 44 those in close contact with a newly diagnosed patient with TB
• those who have had TB before
• people with multiple sexual partners.
• recent immigrants from Africa, Asia, Mexico, and South America
• gastrectomy patients
• people affected with silicosis, diabetes, malnutrition, cancer, Hodgkin's disease, or leukemia
• drug and alcohol abusers
• patients in mental health facilities
• nursing home residents, who are 10 times more likely to contract TB than anyone in the general population
• those receiving treatment with immunosuppressants or corticosteroids
• people with weak immune systems or diseases that affect the immune system, especially those with acquired immunodeficiency syndrome
• prisoners
• homeless persons.

Signs and Symptoms

Symptoms of pulmonary TB include fever, fatigue, loss of appetite and weight, night sweats and persistent cough. Phlegm coughed up may be streaked with blood. Tuberculous pleurisy (affecting the membranes around the lungs) leads to an accumulation of fluid in the pleural cavity (the normally very small space between the membranes) and partial collapse of the lung.

Rarely, the TB in the lung erodes an artery, causing dangerous bleeding into the lung. TB may then spread widely throughout the body via the bloodstream. Meningitis is another dangerous complication.

Diagnostic tests

Several of the following tests may be necessary to distinguish TB from other diseases that may mimic it, such as lung carcinoma, lung abscess, pneumoconiosis, and bronchiectasis.

Chest X-rays show nodular lesions, patchy infiltrates (mainly in upper lobes), cavity formation, scar tissue, and calcium deposits. They may not help distinguish between active and inactive TB.

A tuberculin skin test reveals that the patient has been infected with TB 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 (greater than or equal to a 10-mm induration) develops within 2 to 10 weeks after infection with the tubercle bacillus in both active and inactive TB.

Stains and cultures of sputum, cerebrospinal fluid, urine, drainage from abscess, or pleural fluid show heat-sensitive, nonmotile, aerobic. acid-fast bacilli.

Computed tomography scans or magnetic resonance imaging 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.

Treatment

Antitubercular therapy with daily oral doses of isoniazid, rifampin, and pyrazinamide (with ethambutol added in some cases) for at least 6 months usually cures TB. After 2 to 4 weeks, the disease is no longer infectious and the patient can resume normal activities while continuing to take medication.

The patient with atypical mycobacterial disease or drug-resistant TB may require second-line drugs, such as capreomycin, streptomycin, paraaminosalicylic acid, pyrazinamide, and cycloserine.

Prevention

Treatment to prevent TB in a single person aims to kill walled-up germs that are doing no damage right now, but could break out years from now and become active.

• If you should be treated to prevent sickness, your doctor usually prescribes a daily dose of isoniazid (also called INH), an inexpensive TB medicine.
• You will take INH for up to a year, with periodic checkups to make sure you are taking it as prescribed and that it is not causing undesirable side effects.