Tuberculosis

Question 1

What happens in primary TB?

Answer 1

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

Question 2

What is the outcome of primary TB?

Answer 2

80% heal spontaneously + bacteria are eliminated

20%: bacteria encapsulated in a defensive barrier but persist (dormant) in otherwise healthy individual

Question 3

What is secondary TB? What is it usually precipitated by? Where does it usually occur?

Answer 3

Reactivation of semi-dormant TB
Precipitated by impaired immune function: malnutrition, AIDS or immunosuppressive therapy.
Occurs in lung apices

Question 4

5 RFs for TB

Answer 4

Exposure to TB pt
Ethnic minority groups (sub-saharan Africa + S. Asia)
Homeless, alcoholics, IVDU
HIV+
Immunosuppression

Question 5

How do primary and secondary tuberculosis patients present?

Answer 5

1: usually asymptomatic.
2: variable + nonspecific

Question 6

What genitourinary, musculoskeletal, CNS, and GI symptoms may arise from caseous tubercles spreading in miliary TB?

Answer 6

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

Question 7

What is TB?

Answer 7

Granulomatous disease caused by Mycobacterium tuberculosis

Question 8

What are the 3 subtypes of TB?

Answer 8

Primary: initial infection; pulmonary or GI (rare)
Post-primary: Reinfection/ reactvation
Miliary: Haematogenous dissemination

Question 9

Give 4 features of Mycobacterium Tuberculosis

Answer 9

Intracellular organism
Acid fast bacilli
Survives after being phagocytosed by macrophages
Aerobe: prefers upper lung lobes

Question 10

List 6 signs and symptoms in primary TB

Answer 10

Mostly ASYMPTOMATIC/ vague flu Sx
Fever  
Malaise  
Cough  
Wheeze  
Erythema nodosum 
Phlyctenular conjunctivitis

Question 11

List 7 symptoms in post-primary TB

Answer 11

Fever/ night sweats  
Malaise  
Weight loss  
SOB 
Cough with purulent, blood streaked sputum  
Pleuritic chest pain  
Clubbing

Question 12

List 6 signs and symptoms in miliary TB

Answer 12

Fever  
Weight loss  
Cough
SOB
Meningitis
Yellow caseous tubercles spread to other organs

Question 13

What investigations should be performed for TB?

Answer 13

CXR
Sputum sample AFB +ve + NAAT
Raised WCC + Anaemia
HIV Test

Question 14

What is seen on CXR in primary TB?

Answer 14

Peripheral consolidation

Hilar lymphadenopathy

Question 15

What is seen on CXR in post-primary TB?

Answer 15

Upper lobe shadowing  
Streaky fibrosis + cavitation  
Calcification  
Pleural effusion 
Hilar lymphadenopathy

Question 16

What is seen on CXR in miliary TB?

Answer 16

Fine shadowing

Nodular

Question 17

What group of antibiotics are used to treat TB?

Answer 17

Rifampicin (6months)
Isoniside (6months)
Pyrazinamide (2months)
Ethambutol (2months)

Question 18

What is extra pulmonary TB? In which patients does this most commonly occur?

Answer 18

TB involving organs other than the lungs

Immunocomprimised

Question 19

What lymph/ derm/ CVS/ Adrenal signs and Sx may arise from caseous tubercles spreading in miliary TB?

Answer 19

Lymphadenopathy
Lupus vulgaris
Pericardial effusion, constrictive pericarditis
Addisons

Question 20

What is the gold standard investigation for TB? What is the issue of relying on this?

Answer 20

Sputum culture + Ziehl-Nielsen staining

Culturing TB takes a long time (~ 6 weeks)

Question 21

When are IGRAs useful? What occurs?

Answer 21

Useful in latent TB (high specificity)
Negative in BCG vaccine
Exposure of host T cells to TB antigens leads to release of interferon

Question 22

Why is IGRA testing preferred to TSTs?

Answer 22

Single patient visit

BCG does NOT give false positive

Question 23

What are the 2 forms of testing for TB?

Answer 23

Tuberculin Tests: Mantoux test +Heaf Test

Interferon Gamma Tests (IGRA)

Question 24

How should cultures be taken in suspected TB?

Answer 24

Sputum acid-fast bacilli smear (3 samples 8 hours apart, with 1 being in early morning)

Question 25

What is shown by tuberculin skin tests?

Answer 25

Positive if previous exposure to TB or BCG

Negative TST doesn’t rule out TB

Question 26

What is the Mantoux test? What does it identify?

Answer 26

Erythema after 72hrs of PPD injection suggests patient has previously been exposed to TB.
Identifies those exposed to TB
DOES NOT distinguish between active + latent TB.

Question 27

What is the Heaf test? How is it interpreted?

Answer 27

PPD on forearm. Graded according to papule size + vesiculation
(ring-shaped induration)

Question 28

What is the limitation of the IGRA test?

Answer 28

Does NOT differentiate between latent + active TB

Question 29

What is a Gohn focus?

Answer 29

Granuloma in which central tissue has died due to caseous necrosis
Sequela of primary TB infection

Question 30

What is a Ghon complex comprised of? What may this progress to if calcified?

Answer 30

Ghon focus + ipsilateral mediastinal lymphadenopathy 
Ranke complex (Calcified Ghon + LN)

Question 31

Which anti-TB antibiotic causes optic neuritis? How may this present?

Answer 31

Ethambutol

Loss of colour vision + visual acuity

Question 32

Which anti-TB antibiotic is an enzyme inducer? Thus what drugs need to be considered?

Answer 32

Rifampicin

OCP

Question 33

Which anti-TB antibiotic causes peripheral neuropathy?

Answer 33

Isoniazid

Question 34

Which anti-TB antibiotics are hepatotoxic?

Answer 34

Rifampicin
Isoniazid
Pyrazinamide