Tuberculosis Pathology

Pathology of Tuberculosis: Aetiology, Diagnosis, and Impact

• Tuberculosis (TB) is an ancient disease that became a major public health problem during the Industrial Revolution.

• TB is caused by an infection with Mycobacterium tuberculosis, which is spread mostly through airborne droplets and dust particles.

• TB infects one-third of the world's population, but only 10% of those infected develop clinical disease.

• Persons at high risk for developing TB disease include those who have been recently infected with TB bacteria, and those with medical conditions that weaken the immune system.

• TB diagnosis involves skin tests, microbiological sampling, blood tests, molecular testing, and imaging.

• Active TB infection presents with symptoms such as a persistent cough, fatigue, weight loss, loss of appetite, fever, coughing up blood, and night sweats.

• Granulomatous inflammation is a form of chronic inflammation characterized by groups of activated macrophages, T lymphocytes, and sometimes necrosis.

• The body's attempt to section off an offending agent that is difficult to eradicate often causes damage to healthy tissue.

• The primary lesion of granulomatous inflammation is called a Ghon focus, and the Ghon complex involves a Ghon focus and infection of adjacent lymphatics and hilar lymph nodes.

• TB can spread via pulmonary veins to any organ, causing miliary TB of lung, and if few organisms invade the bloodstream, they can remain latent in an organ for years.

• Eradication of TB has been difficult due to issues such as resistance to anti-TB medications, the limitations of the BCG vaccination, and the global epidemic of HIV that weakens the immune system.

• The impact of COVID-19 has led to a reduction in TB care and an increase in TB deaths globally, with WHO maintaining a TB elimination target of 2035.Overview of Mycobacterium tuberculosis and Tuberculosis

• Mycobacterium tuberculosis infects one-third of the world's population, but only 10% of those infected develop clinical disease.

• The bacterium is usually acquired by inhaling aerosolized droplet nuclei.

• Infection may elicit a cellular immune response that controls infection or a host immune response responsible for the pathologic features of the disease.

• Active tuberculosis (TB) most often causes pulmonary disease associated with fever, weight loss, and drenching night sweats.

• TB is usually diagnosed by microscopy and culture of sputum.

• TB can cause illness that begins soon after initial infection (primary disease) or can remain latent for years before reactivating and causing illness (endogenous reactivation).

• TB is more risky for those who are immuno-compromised (HIV).

• Enlargement of caseation of lymph nodes can erode into bronchial wall or vessel, leading to tuberculous bronchopneumonia or miliary or isolated organ TB.

• Apical lesion of caseating granuloma is not lymph nodes, and immune response is activated for healing by fibrosis.

• Apical lesion enlargement can result in a large mass with little collagen, leading to an increased risk of erosion into vasculature/bronchi.

• In case of erosion into bronchus, live bacilli can be found in sputum, indicating open TB.

• In case of erosion into vessel, it can cause miliary or isolated organ TB.

Pathology of Tuberculosis: Aetiology, Diagnosis, and Impact

• Tuberculosis (TB) is an ancient disease that became a major public health problem during the Industrial Revolution.

• TB is caused by an infection with Mycobacterium tuberculosis, which is spread mostly through airborne droplets and dust particles.

• TB infects one-third of the world's population, but only 10% of those infected develop clinical disease.

• Persons at high risk for developing TB disease include those who have been recently infected with TB bacteria, and those with medical conditions that weaken the immune system.

• TB diagnosis involves skin tests, microbiological sampling, blood tests, molecular testing, and imaging.

• Active TB infection presents with symptoms such as a persistent cough, fatigue, weight loss, loss of appetite, fever, coughing up blood, and night sweats.

• Granulomatous inflammation is a form of chronic inflammation characterized by groups of activated macrophages, T lymphocytes, and sometimes necrosis.

• The body's attempt to section off an offending agent that is difficult to eradicate often causes damage to healthy tissue.

• The primary lesion of granulomatous inflammation is called a Ghon focus, and the Ghon complex involves a Ghon focus and infection of adjacent lymphatics and hilar lymph nodes.

• TB can spread via pulmonary veins to any organ, causing miliary TB of lung, and if few organisms invade the bloodstream, they can remain latent in an organ for years.

• Eradication of TB has been difficult due to issues such as resistance to anti-TB medications, the limitations of the BCG vaccination, and the global epidemic of HIV that weakens the immune system.

• The impact of COVID-19 has led to a reduction in TB care and an increase in TB deaths globally, with WHO maintaining a TB elimination target of 2035.Overview of Mycobacterium tuberculosis and Tuberculosis

• Mycobacterium tuberculosis infects one-third of the world's population, but only 10% of those infected develop clinical disease.

• The bacterium is usually acquired by inhaling aerosolized droplet nuclei.

• Infection may elicit a cellular immune response that controls infection or a host immune response responsible for the pathologic features of the disease.

• Active tuberculosis (TB) most often causes pulmonary disease associated with fever, weight loss, and drenching night sweats.

• TB is usually diagnosed by microscopy and culture of sputum.

• TB can cause illness that begins soon after initial infection (primary disease) or can remain latent for years before reactivating and causing illness (endogenous reactivation).

• TB is more risky for those who are immuno-compromised (HIV).

• Enlargement of caseation of lymph nodes can erode into bronchial wall or vessel, leading to tuberculous bronchopneumonia or miliary or isolated organ TB.

• Apical lesion of caseating granuloma is not lymph nodes, and immune response is activated for healing by fibrosis.

• Apical lesion enlargement can result in a large mass with little collagen, leading to an increased risk of erosion into vasculature/bronchi.

• In case of erosion into bronchus, live bacilli can be found in sputum, indicating open TB.

• In case of erosion into vessel, it can cause miliary or isolated organ TB.

Pathology of Tuberculosis

• Tuberculosis is caused by Mycobacterium tuberculosis, which is an obligate aerobe, acid-fast, non-motile, and slow-growing bacteria.
• TB infection can result in either latent TB infection or active TB disease, with the latter being infectious and requiring treatment.
• Diagnosis of TB can be done through blood tests such as Interferon-Gamma Release Assays (IGRAs) or molecular testing using nucleic acid amplification tests (NAATs).
• Symptoms of TB include persistent cough, weight loss, fever, night sweats, and hemoptysis if cavitation occurs.
• The granulomatous inflammation seen in TB is characterized by groups of activated macrophages, T lymphocytes, and sometimes necrosis. This is the body's attempt to section off the offending agent, which can be damaging to healthy tissue.
• Transmission of TB occurs through exposure to persons with active TB disease, who project high numbers of bacteria in coughs.
• The pathogenesis of TB involves the manipulation of endosomes, defective phagolysosome formation, mycobacterial proliferation in macrophages, and the activation of macrophages by Th1 cells.
• The primary lesion of granulomatous inflammation in TB is the Ghon focus, which can progress to the Ghon complex if adjacent lymphatics and hilar lymph nodes are infected.
• TB can spread through caseating tubercle erosion into lung vasculature, leading to systemic dissemination to any organ via pulmonary vein. If the pulmonary artery is involved, miliary TB of the lung can occur.
• Miliary TB of the lung and spleen is a serious, life-threatening illness characterized by the appearance of hundreds of tiny spots similar to millet seeds in various tissues.
• TB can be classified as secondary or primary, with the latter being subpleural caseous granuloma (Ghon focus) and the former being apical lesion of caseating granuloma.
• Active TB is usually diagnosed by microscopy and culture of sputum, and it is more risky for those who are immunocompromised, such as those with HIV.