Tuberculosis Flashcards
What happens in primary TB?
1st encounter
Lung macrophages in lung engulf organisms + carry them to hilar LN in attempt to control infection.
Small granulomas (tubercles) are formed around the body to contain mycobacteria
What is the outcome of primary TB?
80% heal spontaneously + bacteria are eliminated
20%: bacteria encapsulated in a defensive barrier but persist (dormant) in otherwise healthy individual
What is secondary TB? What is it usually precipitated by? Where does it usually occur?
Reactivation of semi-dormant TB
Precipitated by impaired immune function: malnutrition, AIDS or immunosuppressive therapy.
Occurs in lung apices
5 RFs for TB
Exposure to TB pt Ethnic minority groups (sub-saharan Africa + S. Asia) Homeless, alcoholics, IVDU HIV+ Immunosuppression
How do primary and secondary tuberculosis patients present?
1: usually asymptomatic.
2: variable + nonspecific
What genitourinary, musculoskeletal, CNS, and GI symptoms may arise from caseous tubercles spreading in miliary TB?
GU: Sterile pyuria, Infertility
MSK: pain, arthritis, osteomyelitis, Pott’s disease, spinal cord comp. + abscess formation
CNS: meningitis + tuberculomas: headaches, vomiting
GI: Subacute obstruction, CIBH, Weight loss, Peritonitis, Ascites
What is TB?
Granulomatous disease caused by Mycobacterium tuberculosis
What are the 3 subtypes of TB?
Primary: initial infection; pulmonary or GI (rare)
Post-primary: Reinfection/ reactvation
Miliary: Haematogenous dissemination
Give 4 features of Mycobacterium Tuberculosis
Intracellular organism
Acid fast bacilli
Survives after being phagocytosed by macrophages
Aerobe: prefers upper lung lobes
List 6 signs and symptoms in primary TB
Mostly ASYMPTOMATIC/ vague flu Sx Fever Malaise Cough Wheeze Erythema nodosum Phlyctenular conjunctivitis
List 7 symptoms in post-primary TB
Fever/ night sweats Malaise Weight loss SOB Cough with purulent, blood streaked sputum Pleuritic chest pain Clubbing
List 6 signs and symptoms in miliary TB
Fever Weight loss Cough SOB Meningitis Yellow caseous tubercles spread to other organs
What investigations should be performed for TB?
CXR
Sputum sample AFB +ve + NAAT
Raised WCC + Anaemia
HIV Test
What is seen on CXR in primary TB?
Peripheral consolidation
Hilar lymphadenopathy
What is seen on CXR in post-primary TB?
Upper lobe shadowing Streaky fibrosis + cavitation Calcification Pleural effusion Hilar lymphadenopathy
What is seen on CXR in miliary TB?
Fine shadowing
Nodular
What group of antibiotics are used to treat TB?
Rifampicin (6months)
Isoniside (6months)
Pyrazinamide (2months)
Ethambutol (2months)
What is extra pulmonary TB? In which patients does this most commonly occur?
TB involving organs other than the lungs
Immunocomprimised
What lymph/ derm/ CVS/ Adrenal signs and Sx may arise from caseous tubercles spreading in miliary TB?
Lymphadenopathy
Lupus vulgaris
Pericardial effusion, constrictive pericarditis
Addisons
What is the gold standard investigation for TB? What is the issue of relying on this?
Sputum culture + Ziehl-Nielsen staining
Culturing TB takes a long time (~ 6 weeks)
When are IGRAs useful? What occurs?
Useful in latent TB (high specificity)
Negative in BCG vaccine
Exposure of host T cells to TB antigens leads to release of interferon
Why is IGRA testing preferred to TSTs?
Single patient visit
BCG does NOT give false positive
What are the 2 forms of testing for TB?
Tuberculin Tests: Mantoux test +Heaf Test
Interferon Gamma Tests (IGRA)
How should cultures be taken in suspected TB?
Sputum acid-fast bacilli smear (3 samples 8 hours apart, with 1 being in early morning)
