Tuberculosis

Question 1

What happens in the inital phase of TB exposure?

Answer 1

Alveolar Macrophages recognise bacterium and consume in phagosome
TB, once inside phagosome, releases protein that inhibits the fusion with lysosomes for enzyme breakdown.
Survives and proliferates – produces localised infection

Question 2

what mechanisms lead to the latent phase of TB?

Answer 2

Immune cells surround site of TB infection creating a Granuloma
Formation of a ghon complex. Some cases Tb is killed, other TB remains viable.

Question 3

what is a ghon complex?

Answer 3

Ghon Focus - Tissue inside granuloma dies – caseous necrosis
TB also enters hilar lymph nodes – casesous occurs there
Occur subpleural, lower lobes
Ranke Complex - fibrosis and calcification of ghon complexes

Question 4

what leads to reactivation of TB?

Answer 4

If the immune system is compromised:
o Ghon focus can become reactivated
o TB can spread upper lobes of lungs
o Memory T cells release cytokines
o Cytokines forms more areas of caseous necrosis
o This forms cavities, causing TB dissemination - Lungs + Vascular

Question 5

what is the cause of TB

Answer 5

mycobacterium tuberculosis

Also m.bovis, m.africanum

Question 6

what are the features of mycobacterium tuberculosis?

Answer 6

o Strict Aerobes
o Waxy cell wall – mycolic acid = acid fast (holds onto acid despite
o Hardy – resists weak infections, survives on surfaces for long periods

Question 7

what are the risk factors for TB?

Answer 7

o HIV
o Overcrowding/close contact with active case
o Ethnic minority groups
o Malnutrition, IV drug use, alcohol, Homelessness, poverty
o Chronic lung disease
o Immunosuppression – chemotherapy, biological agents
o Old, young

Question 8

what are the constitutional symptoms associated with TB?

Answer 8

Fever + chills
night sweats
fatigue
loss of appetite
weight loss
lymphadenopathy

Question 9

what are the pulmonary symptoms of TB?

Answer 9

cough +/- haemoptysis

SOB

Question 10

What are the CNS features of TB?

Answer 10

meningitis: neck stiffness, headache, photophobia

Question 11

What are the eye features of TB?

Answer 11

choroiditis: blurred vision, red eye

Question 12

What are the CVS features of TB?

Answer 12

constrictive pericarditis: chest pain, SOB

Question 13

What are the renal features of TB?

Answer 13

dysuria, haematuria (sterile pyuria)

Question 14

What are the GI symptoms of TB?

Answer 14

ileocaecal: abdo pain, mass in RIF
peritoneal: distended abdomen and ascites

Question 15

What are the skeletal symptoms of TB?

Answer 15

(if occurs in the spine potts disease)

Arthritis and osteomyelitis: joint/bone pain localised swelling

Question 16

what are the skin symptoms of TB

Answer 16

lupus vulagaris: brown plaques which can ulcerate and can occur at mucocutaneous junction

Question 17

What tests can be used for Tb diagnosis?

Answer 17

PPD intradermal skin test
IGRA
Chest Xray
Sputum staining, culture, PCR

Question 18

What is a PPD

Answer 18

Purified protein derivative (PPD) intradermal skin test
Tuberculin injected and if previously exposed immune system reacts
If large enough area of redness = positive
Indicates exposed at some point, doesn’t say if active or latent

Question 19

What is the treatment of TB

Answer 19

• Multidrug regimen for prolonged period in active disease (isoniazid and rifampicin, pyrazinamide and ethambutol)
o All 4 for 2 months, then, 4 months pf rifampicin + isoniazid
Single antibiotic for latent TB for 3-6 months
BCG vaccine

Question 20

what are the differentials for TB?

Answer 20

Carcinomas
Pneumonia
PUO
Lymphoma
Fibrotis lung diseases (e.g. sarcoidosis)