Tuberculosis

03/06/2013 by admin | Respiratory

Tuberculosis

Incidence

Worlds leading cause of death from a single infectious disease, with two million deaths in 2000.

This is a result of:

  1. Inadequate programmes for disease control with poorly supervised treatment (no DOTs)
  2. Multiple drug resistance (MDR/XDR-TB): 6-7% is MDR, 25% of which is XDR. MDR-TB is resistant to R&I. XDR-TB has 98% mortality in 1/12.
  3. Co-infection with HIV (70% of Africa co-infected).
  4. A rapid rise in the world’s population of young adults = the age group with the highest mortality from TB
  5. Overcrowding and poor nutrition

 

In the UK:

  1. ~8000 cases/y
  2. 39% cases from London
  3. 72% cases of immigrant status.

 

Classification:

  1. Primary = first infection
  2. Post-primary – reactivation of old primary.

 

Presentation: apical lung cavitation

Primary TB p/c: 30-34yo, asymptomatic, vague cough, wheeze, small pleural effusion, erythema nodosum. Occasionally persistant collapse can give rise to bronchiectasis in the middle lobe = Brock’s syndrome.

Post-primary tuberculosis p/c: 70-74yo, fatigue, malaise, anorexia, weight loss, chest ache, pleural effusion/pneumonia, pleuritic pain, dyspnoea, haemoptysis, fever,

RFs for TB: silicosis (x30 risk), CRF (x10-25), DM (x2-4), low body weight, IVDU…

Diagnostic/Investigation

  1. Chest xray and CT scan – visualise lesion / cavitation
  2. Staining
    1. o Sputum is stained with Ziehl-Neelsen stain ( CANNOT be Gram stained due to waxy capsule) for acid and alcohol-fast bacilli (ZNS for AAFB).
  3. Culture
    1. o Sputum is cultured on Ogana or Lowenstein-Jensen medium for 4-8 weeks.
  4. Fibreoptic bronchoscopy
    1. o With washing of affected lobes if no sputum is available – or broncho-alveolar lavage (BAL)
  5. Biopsy

Aetiology

Mycobacterium tuberculosis (MTB): small, aerobic, non-motile, high lipid content, Gram +ve (but cannot be stained due to capsule), ZNS will show AAFB

Mycobacterium complex: M.bovis, M.africanuum, M.canetti, M.microti

Pathophysiology

The first infection with M.tuberculosis = Primary Tuberculosis.

  1. Usually subpleural, often in mid to upper zones = Ghon focus
  2. Within a few hours of reaching the lung, tubercle bacilli reach the lymph nodes and go into blood.
  3. Initial reaction is an exudative response and infiltration with neutrophil granulocytes.
  4. These are rapidly replaced by macrophages that ingest the bacilli.
  5. Interact with T lymphocytes
  6. Development of cellular immunity by 3-8 weeks after initial infection.
  7. Also get delayed hypersensitivity reaction which results in tissue necrosis and results in the pathology of tuberculosis.
  8. Development of granulomatous lesions
  9. Central area of necrotic caseation material, surrounded by epithelioid cells and Langhan’s giant cells with multiple nuclei. (Both cells derived from macrophages).
  10. Heal and become calcified.
  11. 20% contain tubercle bacilli

 

Adult post-primary tuberculosis: Reactivation leads to post-primary tuberculosis with cavitation (second lesion = Assman focus). Gradual onset of symptoms over weeks and months

Miliary tuberculosis can occur within a year of the primary infection.

  1. Result of acute dissemination of tubercle bacilli via the blood stream.
  2. Difficult diagnosis especially in older people.
  3. Fatal without treatment – aggressive sepsis!
  4. Occasionally presents as tuberculous meningitis.
  5. Mantoux test is usually positive
    1. o Negative in very severe disease.

 

Extrapulmonary TB:

  1. Involve LNs, bone (Pott’s disease of the spine), joints, soft tissue, GU.
  2. More common in the immunosuppressed.

 

Treatment/management

Rifampicin

  1. Induces liver enzymes which are elevated in serum of patients.
  2. Stop drug if bilirubin is elevated or liver transferases are >3x elevated.
  3. Stains body secretions orange.
  4. Oral contraceptive is not effective – use alternative form of contraception.

 

Isoniazid

  1. Few unwanted side effects
  2. May produce polyneuropathy in high doses
    1. o Prescribe pyridoxine (Vit B6) to prevent this

 

Pyrazinamide

  1. Hepatic toxicity
  2. Reduces the renal excretion of urate and may precipitate gout

 

Ethambutol

  1. Dose-related optic retrobulbar neuritis
  1. o Presents with colour blindness for green, reduction in visual acuity and central scotoma.
  2. o Usually reverses when drug stopped.

 

Regime: 1st 2/12 RIPE, further 4/12 just R&I. to be conducted under DOT to maximise compliance.

Prevention

BCG vaccination 

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