SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 012

 1. Discuss the main pathologic characteristics of primary tuberculosis.

Primary tuberculosis develops in individuals not previously exposed to Mycobacterium tuberculosis. The primary lesion, called the Ghon focus, usually forms in the subpleural region of the lower part of the upper lobe or the upper part of the lower lobe.

The bacilli spread through lymphatics to the hilar lymph nodes. The combination of the Ghon focus and involved hilar lymph nodes constitutes the Ghon complex.

Histologically, granulomas composed of epithelioid cells, Langhans giant cells, and lymphocytes surround central caseous necrosis. Fibrosis and calcification commonly occur during healing.

Most primary infections are asymptomatic and heal spontaneously. In immunocompromised individuals, progressive primary tuberculosis may develop with extensive pulmonary and systemic disease.

2. What are the main pathologic characteristics of secondary pulmonary tuberculosis and tuberculous bronchopneumonia?

Secondary pulmonary tuberculosis develops in previously sensitized individuals due to reactivation or reinfection with Mycobacterium tuberculosis.

The lesions usually involve the apical segments of the upper lobes where oxygen tension is highest. Caseating granulomas with central necrosis are the characteristic pathological feature. Progressive disease leads to cavitation caused by liquefaction of caseous material. Fibrosis and calcification are common in healing lesions.

Tuberculous bronchopneumonia occurs when infected material spreads through the bronchi to adjacent lung tissue. Numerous patchy areas of caseating consolidation develop throughout the lungs.

Extensive pulmonary destruction may lead to respiratory failure. Hematogenous spread may result in miliary tuberculosis. Untreated disease may become chronic and highly infectious.

3. Define miliary tuberculosis and tuberculous bronchopneumonia.

Miliary tuberculosis is a disseminated form of tuberculosis resulting from hematogenous spread of Mycobacterium tuberculosis. Numerous tiny millet seed-sized granulomas develop simultaneously in the lungs and other organs.

Commonly affected organs include the liver, spleen, kidneys, bone marrow, meninges, and adrenal glands. It is a life-threatening condition requiring prompt diagnosis and treatment. Tuberculous bronchopneumonia develops when tuberculous material spreads through the bronchial tree. Multiple patchy foci of caseating inflammation appear in different parts of the lungs.

 The lesions resemble bronchopneumonia but contain tuberculous granulomas. Patients usually have fever, cough, and progressive respiratory symptoms.

Both conditions indicate active and widespread tuberculosis. Early antitubercular therapy significantly improves prognosis.

4. Which histologic and laboratory methods are useful in the diagnosis of tuberculosis?

Histologically, tuberculosis is identified by caseating granulomas composed of epithelioid histiocytes, Langhans giant cells, lymphocytes, and central caseous necrosis. Ziehl–Neelsen staining demonstrates acid-fast bacilli within tissue or sputum.

Auramine-rhodamine fluorescent staining increases detection sensitivity. Sputum smear microscopy remains a widely used diagnostic method. Mycobacterial culture is the gold standard for confirming infection and determining drug susceptibility.

Nucleic acid amplification tests, such as GeneXpert MTB/RIF, rapidly detect tuberculosis and rifampicin resistance. Tuberculin skin testing and interferon-gamma release assays identify prior exposure. Chest radiography and CT scanning demonstrate characteristic pulmonary lesions.

Histopathology combined with microbiological confirmation establishes the diagnosis. Molecular techniques have greatly improved early detection.

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DR.C.GANESAN M.D

PROFESSOR OF MEDICINE