Tuberculosis (TB) is an infectious disease that primarily affects the lung parenchyma.
It also may be transmitted to other parts of the body, including the meninges, kidneys, bones, and lymph nodes (Extra pulmonary Tuberculosis).
The primary infectious agent, Mycobacterium tuberculosis, is an acid-fast aerobic rod that grows slowly and is sensitive to heat and ultraviolet light.
Different Categories of Tuberculosis
Latent TB Infection
Many of those who are infected with TB do not develop overt disease. They have no symptoms and their chest x-ray may be normal.
The only manifestation of this encounter may be reaction to the tuberculin skin test (TST).
The risk to be an active disease is increased by other illnesses such as HIV or medications which compromise the immune system.
Active TB Disease
Active TB is an illness in which the TB bacteria are rapidly multiplying and invading different organs of the body.
A person with active pulmonary TB disease may spread TB to others by airborne transmission of infectious particles coughed into the air.
Miliary TB
Miliary TB is a rare form of active disease that occurs when TB bacteria find their way into the blood stream.
In this form, the bacteria quickly spread all over the body in tiny nodules and affect multiple organs at once. This form of TB can be rapidly fatal.
Transmission and Risk Factors
- TB spreads from person to person by airborne transmission.
- An infected person releases droplet nuclei through talking, coughing, sneezing, laughing, or singing. Larger droplets settle; smaller droplets remain suspended in the air and are inhaled by the susceptible person.
Pathophysiology of TB
Inhalation of tubercle bacilli
Reach the alveoli of the lungs
Ingested by alveolar macrophages
Accumulation of exudate in the alveoli, causing bronchopneumonia.( 2 to 10 weeks after exposure).
A small number of the bacilli spread through the blood stream to the apex of the lung, the kidneys, the brain, the bones, and through the lymphatic channels to regional lymph nodes (Extra pulmonary TB).
new tissue masses of live and dead bacilli, are surrounded by macrophages( granulomas).
Granulomas are then transformed to a fibrous tissue mass.
Then becomes necrotic, forming a cheesy mass.
This mass may become calcified and form a collagenous scar.
At this point, the bacteria become dormant, and there is no further progression of active disease (Latent TB). • After initial exposure and infection or inadequate immune system response.
Active disease also may occur with re infection and activation of dormant bacteria.
In this case, the cheesy material is released into the bronchi
Assessment and Diagnostic Findings
- A complete history,
- Physical examination,
- Tuberculin skin test,
- Chest x-ray,
- Sputum culture are used to diagnose TB.
MANTOUX TUBERCULIN SKIN TEST (TST)
The Mantoux tuberculin skin test, or TST, is performed by placing an intradermal injection of 0.1 ml of purified protein derivative (PPD) containing 5 tuberculin units (TU) into the intradermal layer of the inner aspect of the forearm.
This should produce a wheal 6 mm to 10 mm in diameter. Institutional guidelines regarding universal precautions for infection control (e.g., use of gloves) should be followed . The reaction to the TST should be read 48 to 72 hours after the injection by a trained healthcare worker.
The reaction is read by measuring in millimeters the diameter of induration (palpable raised hardened area) across the forearm. If there is no induration, the result should be recorded as 0 mm. The area of erythema should not be measured, just the induration.
Interpretation of Results
The size of the induration determines the significance of the reaction.
A reaction of 0 to 4 mm is considered not significant;
a reaction of 5 mm or greater may be significant in individuals who are considered at risk.
An induration of 10 mm or greater is usually considered significant in individuals who have normal or mildly impaired immunity.
A significant reaction indicates that a patient has been exposed to M. tuberculosis recently or in the past or has been vaccinated with bacille Calmette-Guerin (BCG) vaccine.
Medical Management
- Pulmonary TB is treated primarily with (antituberculosis agents) for 6 to 12 months.
- A prolonged treatment duration is necessary to ensure eradication of the organisms and to prevent relapse.
- In current TB therapy, five first-line medications are used: isoniazid (INH), rifampin, pyrazinamide, and either streptomycin or ethambutol.
- second-line medications. Capreomycin, ethionamide, paraaminosalicylate sodium, and cycloserine
- Additional potentially effective medications include other aminoglycosides, quinolones, rifabutin, clofazimine, and combinations of medications.
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