TB

• TB is a notifiable disease.
• How is TB transmitted?


  Airborne
• Pathophys of TB 


  Inhalation of TB → deposit in alveoli → engulfed by alveolar macrophages → proliferates in macrophages → release virulence factors → immune response

  • Immediate clearance
  • Majority
  • Primary disease
  • if the immune response is inadequate
  • Latent infection (with or without subsequent reactivation disease)
  • Th1 response → caseating granuloma (caseous centre with necrotic material, surrounded by lymphocytes and macrophages) → successful containment
  • Reactivation disease
  • Occurs when the immune response is suppressed
  • Onset of the active disease years after latent infection
• What is the classification of TB based on anatomical site?


  Pulmonary TB (in lung parenchyma)

  Extrapulmonary TB (outside of lungs)
• What is miliary TB?

  TB affects multiple organs
• What is the classification of TB based on bacteriological status?

  Tuberculin positive

  • Indicates exposure to Mycobacterium tuberculosis or BCG vaccine
  • Does not indicate active disease

  Smear positive

  • AFB (acid-fast bacilli) are detected in sputum smear microscopy

  Smear negative

  • No AFB detected in sputum BUT culture grows Mycobacterium tuberculosis

  Culture negative

  • Neither acid-fast bacilli are detected nor does culture grow Mycobacterium tuberculosis
  • Diagnosis based on clinical or radiological grounds
• What is the classification of TB based on Hx of treatment classification?


  New - Pt never been treated for TB or has taken anti-TB drugs for < 1 month

  Relapse - Pt was previously treated & declared cured, but now diagnosed with recurrent episode of TB

  Treatment after failure - Pt started treatment but bacteriological status remains positive after 5 or more months of treatment

  Treatment after loss to follow-up - Pt returns to treatment, bacteriologically positive, following 2 or more consecutive months of treatment

  Chronic case - Pt remains smear +ve after supervised re-treatment
• How is TB classified based on severity of disease?


  Drug-sensitive TB

  • sensitive to all 1st line anti-TB drugs

  Multidrug-resistant TB

  • resistant to at least isoniazid & rifampicin

  Extensively drug-resistant TB

  • resistant to any fluoroquinolone PLUS at least one 2nd line injectable drug
• What are the signs & symptoms of TB?


  Latent infection = asymptomatic & non-contagious

  Fever

  Night sweats

  Weight loss

  Malaise

  SOB

  Persistent cough (>/= 3 weeks)

  Haemoptysis

  Chest pain

  Crackles

  Bronchial breath sounds
• What are the RFs for TB?


  Exposure to infection

  Living in/visiting endemic country

  Immunodeficiency (inc. HIV)

  Drug/alcohol misuse

  Homelessness/overcrowding

  Imprisonment

  IV drug use

  Malnutrition
• What are the Inx & diagnosis of TB?


  Obs

  Full Hx & exam

  Bloods (FBC, U&E, LFTs, CRP, IGRA)

  CXR

  CT

  Tuberculin skin test (Mantoux test)

  Sputum culture

  Sputum smear microscopy

  Bronchoscopy with bronchoalveolar lavage (BAL)

  Nucleic acid amplification tests (NAATs)

  Tissue biopsy

  HIV testing
• What is IGRA?


  Interferon gamma release assay

  Measure of immune response to TB proteins
• What would a CXR show in TB?


  Consolidation in upper lobes

  Granulomas

  Calcified granulomas (Ghon complex)

  Cannot confirm TB diagnosis
• What is shown in this CXR?


  TB

  
• What is the tuberculin skin test?


  Intradermal injection of purified protein derivative of mycobacterium tuberculosis

  Raised area with diameter of 10mm or more after 48-72 hours suggests TB infection

  Cannot differentiate between latent & active disease
• Sputum culture in TB


  3 x morning sputum samples

  Gold standard for detection of TB

  Can determine drug susceptibility

  Results can take up to 6 weeks
• Sputum smear microscopy in TB


  Ziehl-Neelson stain

  Will show acid-fast bacilli (AFB)
• When is bronchoscopy with bronchoalveolar lavage used?


  In pts who are unable to produce sputum or when smear microscopy is negative but there is high suspicion of pulmonary TB
• When is tissue biopsy used in the diagnosis of TB?


  Suspected extrapulmonary TB
• Why is HIV testing done in TB?


  Often co-exists with TB
• What are the DDx of TB?


  COVID-19

  CAP

  Lung cancer

  Non-TB mycobacterium

  Sarcoidosis

  Fungal infection

  Nocardiosis
• What are the complications of TB?

  Transmission of TB

  Immune reconstitution inflammatory syndrome (IRIS)

  Acute respiratory distress syndrome (ARDS)

  PTX

  Empyema

  Bronchiectasis

  Extensive Lung Destruction
• What is immune reconstitution inflammatory syndrome (IRIS)?


  Transient worsening of TB symptoms & lesions following initiation of anti-TB therapy

  More common in immunocompromised pts
• What is the treatment of latent TB?


  3 months isoniazid (with pyridoxine) + rifampicin

  OR

  6 months isoniazid (with pyridoxine)
• What is the treatment of active TB (w/o CNS involvement)?


  2 months of RIPE (rifampicin, isoniazid (with pyridoxine), pyrazinamide & ethambutol)

  4 further months of RI ((rifampicin, isoniazid (with pyridoxine)
• What is the treatment of active TB (w/ CNS involvement)?


  2 months of RIPE (rifampicin, isoniazid (with pyridoxine), pyrazinamide & ethambutol)

  10 further months of RI ((rifampicin, isoniazid (with pyridoxine))
• What are the side effects of rifampicin?


  Thrombocytopenia

  Discolouration of bodily fluids (turns red/orange)
• What are the side effects of isoniazid?


  Hepatic disorders

  Severe cutaneous adverse reactions (SCARs)
• What are the side effects of pyrazinamide?


  Hepatic disorders

  Sideroblastic anaemia

  Splenomegaly
• What are the side effects of ethambutol?


  Hyperuricaemia

  Nerve disorders

  Visual impairment