COMMENTS
FINDINGS:
Most cases of primary TB are asymptomatic. The most common extrapulmonary sites are lymph nodes, pleura, bones, and joints. [Cecil, p. 2000, 2003] Reactivation TB in adolescents and adults has a predilection for the lung apices probably because of increased oxygen concentrations and/or decreased lymphatic clearance. Lower lobe pneumonia is the pattern more commonly seen in the elderly and in progressive primary infection of childhood. "Pneumonia associated with hilar adenopathy should always suggest primary tuberculosis regardless of the lung fields involved and patient age." [PPID, p. 2996-3000]
Lymphadenitis (usually cervical) is the most common form of extra-pulmonary TB in developing countries. CNS infections include meningitis and tuberculomas of the brain and spinal cord. Findings in renal tuberculosis include hematuria, pyuria, flank pain, and positive AFB stains of the urine sediment. Abdominal TB is still common in developing countries. The clinical presentation may include gastrointestinal bleeding, fever, abdominal mass, bowel obstruction, and acute abdomen secondary to perforation. Rarely, TB patients develop eye infections (uveitis or oculoglandular conjunctivitis); skin infections (nodules or warty growths); or infections of the larynx, sinuses, salivary glands, and adrenal glands. Other complications of TB include pericarditis, epididymo-orchitis, female genital tract infections, arthritis, and osteomyelitis. Worldwide, TB is the most common cause of granulomatous hepatitis--jaundice may occur. Pott's disease involves two adjacent vertebral bodies with narrowing of the intervertebral disc. Miliary TB affects the bone marrow (anemia and thrombocytopenia) and the lungs (dyspnea). [MMWR: Jan 16, 2009]
Pott's disease (tuberculous spondylitis) may cause paralysis, weakness, deformity, and sinus formation. Nodular and ulcerative skin lesions occur, especially in patients with AIDS. Gastrointestinal TB was common in the past before effective drugs were available; patients had diarrhea and abdominal pain. Patients with miliary TB may have cutaneous eruptions, sinus tracts, scrotal masses, and/or lymphadenopathy. [PPID, 8th Ed, p. 2810-17] Anemia and thrombocytopenia are common in miliary TB. Patients may present with shock and ARDS. [Cohen, p. 277-8] Patients with tuberculous meningitis present with headache, vomiting, confusion, stiff neck, and focal neurologic deficits. Patients with brain tuberculomas may have seizures. Hematemesis is a rare complication of esophageal disease after formation of an aortoesophageal fistula. [PPID, 8th Ed, p. 2813-16] Tuberculous meningitis can cause cranial nerve palsies and coma. [Cohen, p. 186] The ulcerations and fistulae of gastrointestinal TB may simulate Crohn's disease. [Harrison ID, p. 622] Renal failure is a complication of renal TB. [Guerrant, Ch. 35]
DIAGNOSTIC TESTS:
TB skin tests (TST) and interferon-gamma release assays (IGRA) usually become positive 8-10 weeks after exposure. The diagnosis of latent TB infection (LTBI) is based on a positive TST or IGRA. It takes 2 weeks to identify M. tuberculosis by culture. Identification of acid fast bacilli is a less sensitive and specific method. Nucleic acid amplification (NAA) testing of sputum is a rapid technique, more sensitive and specific than acid fast staining, but less sensitive than culture. [CDC Travel, p. 356-7] For active TB, AFB stain of sputum is 50% sensitive, and AFB culture is 80% sensitive. TST and IGRA cannot distinguish between latent and active disease. In patients with active disease, >25% of cases will be negative by TST or IGRA. [ABX Guide] The tuberculin skin test is used primarily to detect infection in persons without symptoms; it may be negative in up to 50% of patients with miliary (disseminated) TB. [Harrison ID, p. 623, 617-8] A positive tuberculin skin test will revert to negative in the absence of new aerosol inocula or persisting infection. [PPID, p. 2995] Chronic TB is associated with hypergammaglobulinemia. [MMWR: Jan 16, 2009]
EPIDEMIOLOGY:
M. tuberculosis infects 1/3 of the world’s population and causes over 9 million new cases and 1.7 million deaths (including 230,000 deaths in patients co-infected with HIV) per year. Worldwide, most exposures occur in the household, and only 1/2 of close contacts become infected. Healthcare workers are exposed to tubercle bacilli in airborne droplet nuclei while caring for patients with tuberculosis and while performing bronchoscopies or endotracheal intubations on these patients. Approximately 90%-95% of those newly infected with tuberculosis never develop clinical illness. These individuals have a latent infection that may persist for a lifetime. Silicosis and other debilitating diseases can impair the immune system and increase the risk for activation of latent tuberculosis. In some sub-Saharan areas of Africa, 10%-15% of adults are co-infected with HIV and TB. To become infected, one must breathe the air contaminated by a coughing, sneezing, or talking patient with active TB. The likelihood of infection increases as the exposure period extends longer than just a few minutes or a few hours, e.g., attending to a patient with active TB in a hospital, prison, or homeless shelter. TB is transmitted rarely by direct contact with infected tissues, e.g., a pathologist with a "prosector's wart." The only reservoir for M. tuberculosis is other humans. Many animals are susceptible to infection, and rarely, the disease spreads through infected monkeys, cattle, badgers, swine, and other mammals. TB from milk infected with M. bovis occurs in travelers to some countries, e.g., Mexico. [Merck Manual, p., 1650-60; CCDM, p. 639-50; CDC Travel, p. 356-7; Guerrant, p. 228-245, 921, 999, 1004-5; PPID, p. 2985-3018; Cohen, p. 1135t]
SCOPE
70% of cases: India, China, Indonesia, Pakistan, Bangladesh, Philippines, South Africa, , DR Congo, Nigeria, Myanmar, and Ethiopia; [PPID, p. 2991t]