Tuberculosis Flashcards
What happens in primary TB?
1st encounter
Lung lesion “Ghon focus” develops: composed of tubercle-laden macrophages
Combination of a Ghon focus + hilar LNs = Ghon complex
How is TB transmitted?
Inhalation of respiratory droplets from infectious active pulmonary TB cough
What are the outcomes of primary TB infection?
Immediate clearance. Asymptomatic
TB contained (disease is dormant): caseating granuloma formation. Asymptomatic
Primary disease: TB disseminates due to inadequate immune response
What is secondary TB? What is it usually precipitated by? Where does it usually occur?
Reactivation of dormant TB (5-10% lifetime risk)
Precipitated by impaired immune function
Occurs in lung apices
List 6 risk factors for TB
Born in high prevalence area
Close contact with TB patient
Homeless, alcohol dependent, IVDUs
Immunosuppression
Co-morbidities
Age <5y
List 4 co-morbidities increasing the risk of TB
HIV
DM
End-stage CKD
Occupational lung disease e.g. silicosis
List 3 immunosuppressive drug classes increasing risk of TB
High dose CS
Chemotherapy
Biologics e.g. TNF alpha inhibitors- Infliximab
List 5 constitutional symptoms a patient with TB may complain of
Fever
Night sweats
Weight loss
Anorexia
Malaise
List 3 pulmonary symptoms that occur in TB
Chronic, initially dry, then productive cough; purulent sputum
Dyspnoea
Haemoptysis
What extra-pulmonary symptoms of TB may arise?
Lymphadenopathy
Bone/ joint pain
GI: Abdo pain, constipation, obstruction
GU: Dysuria, haematuria
TB meningitis: Headaches, vomiting
Cutaneous: erythema nodosum
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 4 signs of TB on examination
Fever
Clubbing
Auscultation: crackles, bronchial breath sounds or normal
Wasting
What initial investigations should be performed for suspected active TB?
3x Sputum samples for microscopy, culture + NAAT
CXR
What is used in microscopy for TB and what does this detect?
Ziehl-Neelsen stain for acid-fast bacilli
What is the gold standard investigation for TB? What is the issue of relying on this?
Sputum culture with Lowenstein-Jensen agar
Culturing TB takes a long time (~ 6w)
If unable to produce an adequate sputum sample, what other investigations can be used for TB?
Bronchoalveolar lavage sample, Pleural fluid or gastric aspirate for culture.
Pleural biopsy or lung biopsy if other testing not diagnostic.
What is seen on CXR in primary TB?
Hilar lymphadenopathy
Pleural effusion
Pulmonary infiltrates
Consolidation
What is seen on CXR in post-primary TB?
Upper lobe consolidation
Fibrocaseous cavitary lesions in upper lobes
Calcification
What is the treatment for active TB?
Rifampicin (6 months)
Isonizid (6 months) + Pyridoxine (Via B6)
Pyrazinamide (2 months)
Ethambutol (2 months)
In which patients is directly observed therapy indicated with a 3x a week dosing regimen?
Homeless + active TB
Patients who are likely to have poor concordance
Prisoner with active or latent TB
What is the treatment for latent TB?
Rifampicin + Isoniazid for 3 months
OR
Isoniazid (+ pyridoxine) for 6 months
How does treatment for patients with meningeal TB differ?
Treated for prolonged period >,12 months with the addition of steroids
What is extra pulmonary TB? In which patients does this most commonly occur?
TB involving organs other than the lungs
Immunocomprimised
What lymph, dermatological, CVS and adrenal signs and symptoms may arise from caseous tubercles spreading in miliary TB?
Lymphadenopathy
Skin: lupus vulgaris
Heart: pericardial effusion, constrictive pericarditis
Adrenals: Addisons
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 8h apart, with 1 being in early morning)
What is shown by tuberculin skin tests?
Positive if previous exposure to TB or BCG
Negative TST doesn’t rule out TB
What is the Mantoux test? What does it identify?
Erythema after 72h of PPD injection suggests patient has previously been exposed to TB.
Identifies those exposed to TB
DOES NOT distinguish between active + latent TB.
What is the Heaf test? How is it interpreted?
PPD on forearm. Graded according to papule size + vesiculation
(ring-shaped induration)
What is the limitation of the IGRA test?
Does not differentiate between latent + active TB
What is a Ghon focus?
Granuloma in which central tissue has died due to caseous necrosis
Sequela of primary TB infection
What is a Ghon complex comprised of? What may this progress to if calcified?
Ghon focus + ipsilateral mediastinal lymphadenopathy
Ranke complex
What is a Ranke complex?
a Ghon lesion that has undergone calcification
+
an ipsilateral calcified mediastinal node
Which anti-TB antibiotic is an enzyme inducer? Thus what drugs need to be considered?
Rifampicin
OCP
Give 3 side effects of Rifampicin
Orange / red secretions
CYP450 induction
Raised transaminases
Give 2 side effects of Isoniazid
Peripheral neuropathy (B6 deficiency)
Hepatotoxicity
Give 2 side effects of Pyrazinamide
Hyperuricaemia
Hepatotoxicity
Give a side effect of Ethambutol
Optic neuritis
(Pain, vision loss, 1 eye)
MOA of Rifampicin
inhibits RNA polymerase
MOA of Isoniazid
Decreased mycolic acid synthesis (part of cell wall)
MOA of Pyrazinamide
Unknown
MOA of Ethambutol
Decreased polymerisation of cell wall
