Introduction1
Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (tubercle bacilli).
The lungs are the most common site of involvement in tuberculosis and are a major source of spread of the disease.
Pulmonary manifestations of tuberculosis are varied and depend on whether the infection is primary or post-primary.
Classification2
Pulmonary: involves lung parenchyma and airways.
Primary tuberculosis: infection following first time entry of the bacilli into the body; common sites being upper airways and lungs.Usually seen in children and young adults. Maybe self limiting or progress to progressive primary tuberculosis.
Post primary tuberculosis: adult type of tuberculosis in an otherwise sensitized individual by reactivation of primary focus or by reinfection.
Extra pulmonary: Involvement of pleura, lymph nodes, bone, kidney, brain and genital tract.
Etiology
TB is spread from person to person through air by droplet nuclei. M. tuberculosis may be expelled when an infectious person coughs, sneezes, speaks or sings. Transmission occurs when another person inhales these droplet nuclei.
Pathogenesis
The primary focus (Ghon’s focus) in the lung parenchyma consists of bacteria surrounded by lymphocytes, macrophages, epithelioid cells, giant cells and fibroblasts. Ghon’s focus along with lymphangitis and regional lymphadenopathy is called primary complex (Ghon’s complex). The primary infection is usually asymptomatic. Progression occurs in 5% of patients, usually in those with impaired immunity, and is called progressive primary tuberculosis.
Post-primary pulmonary tuberculosis develops later in adult life as pneumonia involving the upper lobes or superior segment of lower lobes. Pneumonia undergoes caseous necrosis and fibrosis subsequently.
Clinical features
Children with primary complex are mostly asymptomatic. However it can present as fever, loss of appetite and failure to thrive3.
Post primary tuberculosis presents with chronic cough, fever, malaise and weight loss. They may also have hemoptysis. Sometimes massive hemoptysis develops due to erosion of a bronchial artery (Rasmussen’s aneurysm).
Patients with acquired immunodeficiency syndrome have features similar to primary tuberculosis or disseminated tuberculosis.
Workup2
Sputum smear examination for acid fast bacilli (AFB). All patients with cough of more than 2 weeks should undergo sputum smear on 2 consecutive days. It is difficult to obtain sputum in young children and hence gastric aspirate is subjected to AFB smear.
Chest X-ray: All pulmonary TB suspects should undergo X-ray chest examination. X-ray is highly sensitive but not specific. Subcentimeter nodules or hilar lymphadenopathy may be seen3. In post primary TB, X-ray shows cavitating consolidation, fibrosis, miliary shadows and pleural effusion4.
Molecular methods such as TB-PCR, CBNAAT and true NAAT are widely used and are considered highly sensitive.
Sputum for mycobacterial culture is also done to confirm infection and to rule out drug resistance.
Management5
The major goals of treatment include cure the individual patient; minimize risk of death and disability and to prevent airborne transmission.
Tuberculosis must be treated for at least 6 months and in some cases even longer. Most of the bacteria are killed during the first 8 weeks of treatment; however, there are persistent organisms that require longer treatment. If treatment is inadequate, the surviving bacteria may cause relapse, potentially drug-resistant tuberculosis.
Treatment includes;
Intensive phase:8 weeks with 4 drugs- rifampicin, INH, ethambutol, pyrazinamide.
Continuation phase: f 16 weeks with 3 drugs- rifampicin, INH, ethambutol.
Directly Observed Therapy (DOT) is a component of case management that helps ensure patients adhere to therapy. It is the method whereby a trained health-care worker or another trained designated person observes drug intake to ensure compliance.
Prophylaxis
Treatment of latent TB infection by INH monotherapy for 6 months
References
1. Dye C. Global epidemiology of tuberculosis. Lancet 2006; 367: 938-40. [PubMed]
2. National Institute for Health and Clinical Excellence. Tuberculosis: clinical diagnosis and management of tuberculosis, and measures for its prevention and control. London: NICE, 2006. Available at: www.nice.org.uk/page.aspx?o=CG033.
3. Schaaf HS, Beyers N, Gie RB, Schaaf HS, Beyers N, Gie RP, et al. Respiratory tuberculosis in children: the diagnostic value of clinical features and special investigations. Pediatr Infect Dis J 1995; 14: 189-94. [PubMed]
4. Van Dyck P, Vanhoenacker FM, Van den Brande P, De Schepper AM. Imaging of pulmonary tuberculosis. Eur Radiol. 2003; 13:1771–85. [PubMed] [Google Scholar]
5. World Health Organization Stop TB Department. Treatment of tuberculosis: guidelines for national programmes. 3rd ed. Geneva: WHO, 2003.
No comments:
Post a Comment