Tuberculosis (TB) Flashcards
How is M. tuberculosis transmitted? [2]
usually transmitted person-to-person (close contacts) via inhalation of aerosol droplets containing bacterium. M. tuberculosis which enters the lungs and is taken up by the macrophages
Describe primary tuberculosis [6]
- A non-immune host who is exposed to M. tuberculosis may develop primary infection of the lungs leading to the development of a small lung lesion composed of tubercle-laden macrophages known as a Ghon focus
- The macrophages often migrate to regional (hilar) lymph nodes forming a Ghon complex
- Ghon complex leads to the formation of a granuloma, which is a compact, organized aggregate of epithelioid cells with central caseous necrosis
- The inflammatory response is mediated by a type 4 hypersensitivity reaction.
- In immunocompetent people the initial lesion usually heals by fibrosis.
- Those who are immunocompromised may develop disseminated disease (miliary tuberculosis)
Describe the composition of a TB granuloma [9]
- A granuloma a compact, organized aggregate of epithelioid cells with central caseous necrosis.
- These epithelioid cells include:
- Macrophages
- which have undergone a specialized transformation to have tightly interdigitated cell membranes that link adjacent cells
- which can fuse into multinucleated giant cells or differentiate into foam cells, which are characterized by lipid accumulation and are most commonly located at the rim of the necrotic centre of a mature tuberculous granuloma
- Many other cell types also populate the granuloma, such as:
- neutrophils,
- dendritic cells,
- B and T cells,
- natural killer (NK) cells,
- fibroblasts
- cells that secrete extracellular matrix components.
- Epithelial cells which surround the granuloma
Where in a TB granuloma are bacteria most commonly present? [1]
Bacteria are most commonly present in the central necrotic areas in which dead and dying macrophages can be seen.
Describe secondary (post-primary) tuberculosis [3]
- If the host becomes immunocompromised the initial infection may become reactivated.
- Reactivation generally occurs in the apex of the lungs and may spread locally or to more distant sites.
- Possible causes of immunosuppression include:
- immunosuppressive drugs including steroids
- HIV
- malnutrition
Where in the body can secondary TB develop? [6]
- Lungs (most common site)
- Extra-pulmonary infection may occur in the following areas:
- central nervous system (tuberculous meningitis - the most serious complication)
- vertebral bodies (Pott’s disease)
- cervical lymph nodes (scrofuloderma)
- renal
- gastrointestinal tract
What is the Mantoux Test and what happens when it’s positive for TB? [2]
- a test of whether a person has been exposed to TB previously where you inject under the skin PPD (protein antigen from dead TB) and then you check whether this person has memory T cells for TB.
- If positive you get an induration of the skin (i.e. the sides rise up) and then this area of induration is measured.
What are the 2 problems with the Mantoux Test? [2]
- It can’t differentiate between active and latent disease
- It can be confounded in patients who have e.g. had their BCG vaccine (vaccine for TB) or patients who are infected with other non-TB bacteria
What are the 4 most important presenting symptoms of TB? [4]
- cough & sputum
- +/- haemoptysis
- night sweats
- weight loss
What are the pulmonary symptoms of TB? [4]
- Cough & sputum +/- haemoptysis
- Shortness of breath
What are the constitutional symptoms of TB? [6]
- Fever + chills
- Night sweats
- Fatigue
- Loss of appetite/weight loss
- Lymphadenopathy
What are the CNS symptoms of TB? [4]
- meningitis
- neck stiffness
- headache
- photophobia
What are the eye symptoms of TB? [3]
- Choroiditis:
- Blurred vision
- Red eyes
What are the CVS symptoms of TB? [3]
- Constrictive pericarditis:
- Chest pain
- Shortness of breath
What are the renal symptoms of TB? [3]
- Dysuria
- Haematuria
- Sterile pyuria
