Resp - TB

Question 1

TB

Classification

Answer 1

Primary TB
* Describes new tuberculosis infection or active disease in a previously naïve host

Latent TB
* 90% of individuals with intact immunity can control further replication of bacilli after primary infection

Reactivation TB
* Also known as chronic TB or post-primary TB
* Reactivation of previous focus of mycobacterial containment that was seeded at the time of primary infection

Miliary TB
* Clinical disease resulting from hematogenous dissemination of Mycobacterium tuberculosis
* Result from both progressive primary infection or via reactivation of latent focus with
subsequent hematogenous spread via bloodstream
* Spread is limited to lung if pulmonary artery is involved but spread is systemic if the pulmonary vein is involved

Endobronchial TB
* Defined as tuberculous infection of the tracheobronchial tree
* Develop via direct extension to bronchi from an adjacent parenchymal focus or via spread of organisms to bronchi via infected sputum

Extra-pulmonary TB

Question 2

Latent vs Active TB

• Differences in infectivity, presentation, investigations, diagnosis, treatment

Answer 2

Question 3

TB lymphadenitis

Features
Clinical manifestations
Diagnosis
Treatment

Answer 3

Question 4

TB pleuritis

Features
Diagnosis
Treatment

Answer 4

Question 5

Musculoskeletal TB

Types of infection
Diagnosis
Treatment

Answer 5

Question 6

TB meningitis

Staging
Diagnosis
Treatment

Answer 6

Question 7

TB risk factors

Answer 7

Question 8

TB

Risk factor for progression or dissemination

Answer 8

Question 9

Types of mycobacterium

Microbiological features of M.TB

Answer 9

Question 10

Pulmonary TB ddx

Answer 10

Differential diagnosis
 Bronchiectasis
 Pneumonia
 Lung abscess
 Lung cancer
 Sarcoidosis
 Silicosis

Question 11

TB

Infection course
Pathogenesis of primary and reactivated TB

Answer 11

Inhalation of aerosol droplets containing Mycobacterium tuberculosis with subsequent deposition in the lungs leads to 1 of the 4 possible outcomes
- Immediate clearance of the organisms
- Primary disease: Immediate onset of active disease
- Latent infection
- Reactivation disease: Onset of active disease many years following a period of latent infection

Pathogenesis:
Primary disease
- Tubercle bacilli establish infection in the lungs after they are carried in droplets small enough to reach alveolar spaces
- Failure to eliminate the infection by innate defense system leads to proliferation of bacilli inside alveolar macrophages
- Macrophages produce cytokines that attract other phagocytic cells including monocytes, macrophages and neutrophils which eventually form a nodular granulomatous structure known as tubercle
- Activation of cell-mediated immune response (90%) controls infection
- Failure of cell-mediated immune response: Progressive destruction of lung with development of caseating necrosis; Tubercle enlarges and bacilli enters local draining lymph nodes leading to lymphadenopathy

Reactivation disease:
- proliferation of previously latent bacteria seeded at the time of primary infection
- localized with little regional lymph node involvement

Question 12

TB

Clinical presentation

Answer 12

Physical examination
 General examination: Lymphadenopathy
 Palpation: ↓ Chest wall expansion
 Percussion: Stony dullness in pleural effusion
 Auscultation
* ↓ Breath sounds
* Bronchial breathing
* Pain-inspiratory crackles
* Wheezing in endobronchial TB

Question 13

TB

Diagnosis methods

Answer 13

Sampling for pulmonary TB
- Early morning sputum with multiple samples/ induced by inhalation of aerosolized hypertonic saline generated by nebulizer
- Broncho alveolar lavage (BAL): indicated for negative sputum studies with high suspicion of TB
- Fiberoptic bronchoscopy (FOB)
- Transbronchial/ transthoracic needle biopsy

Sampling for extra-pulmonary TB: invasive procedure at tissue + PCR/ Histopathology analysis
e.g. LN FNA for TB lymphadenitis, LP for CSF in TB meningitis, Pleural tap/ pleural biopsy for TB pleuritis

Immunocompromised: IGRA/ TST have no role, require radiological diagnosis

Biochemical:
- CBC with differentials: NcNc anemia, Leukocytosis/ Monocytosis, Thrombocytopenia/ thrombocytosis, Pancytopenia in BM infiltration
- Inflammatory markers
- RFT and electrolyte: HypoNa in SIADH

Immunological tests:
- Tuberculin skin test (Mantoux test) (PPD test)
- Interferon-γ release assay (IGRA) (QuantiFERON-TB GOLD/ T-SPOT
- Urine lipoarabinomannan (LAM) antigen detection

Microbiological tests:
- AFB smear microscopy with Ziehl-Neelsen (ZN) stain
- Mycobacterial culture with Lowenstein-Jensen medium egg-based culture/ BACTEC broth bacsed culture
- Nucleic acid amplification test (NAAT) (e.g. PCR): adjunct test that does not exclude active TB and drug resistance pattern
- Histopathological analysis: Caseating granulomatous inflammation with epithelioid macrophages, Langhans giant cells (horseshoe appearance with nuclei locate peripherally) and lymphocytes

Radiological:
- CXR/ CT chest