SAQ

• Haemoptysis


  Coughing up of blood or blood-stained sputum
• Haemoptysis is always abnormal, so it is a very important indicator of an abnormality in the respiratory system
• A bleeding lesion is likely to be either inflammatory or neoplastic, hence we always take seriously the symptom of haemoptysis
• Common causes of haemoptysis in Fiji

  • Bronchiectasis (in young people who cough up a lot of sputum)
  • Lung carcinoma (in older heavy smokers without previous cough)
  • Tuberculosis (if patient has had symptoms for weeks/months, been in contact with TB case, and has other symptoms like weight loss, fever, night sweats)
• Haemoptysis in tuberculosis


  Anastomoses between bronchial and pulmonary circulation, especially in cavity walls
• Haemoptysis in mitral stenosis

  Markedly elevated left atrial pressure transmitted back into pulmonary circuit, causing rupture of pulmonary veins and capillaries
• Investigations for haemoptysis


  • Chest X-ray (most important single investigation)
  • Sputum examination for acid-fast bacilli (if X-ray suggests tuberculosis)
  • Sputum cytology and bronchoscopy (if X-ray suggests bronchial carcinoma)
  • Thoracic CT scan (to better visualise lung architecture and mediastinal structures)
• Mycobacterium tuberculosis


  • Non-motile, non-sporing, non-capsulated rod
  • Cell wall is very lipid-rich, lipids comprising up to 40% of dry weight
  • Slow growing, with generation time of 15-20 hours
  • Requires special media for growth (LJ, Ogawa)
  • Highly sensitive to UV light and destroyed by heat
  • Survives in organic material for long time if not exposed to sunlight
  • Sensitive to alcohol, formaldehyde, glutareldehyde, and hypochlorites
  • Able to survive within macrophages
• Diagnosis of tuberculosis


  • Often relies on signs and symptoms in developing countries, as laboratory diagnosis requires sophistication
  • Least sophisticated method is Ziehl-Nielson staining of sputum, but this misses 20% of active TB cases
  • Culture of sputum required for those with too few bacilli to be detected by smear, but not available in most hospitals in the Pacific
  • Patients with extra-pulmonary TB not diagnosed by sputum smear or culture
• Mantoux skin test


  1. Standard amount of tuberculoprotein (antigen from TB cell wall) injected intradermally

  2. T-cells sensitised during prior TB exposure migrate to site, process antigen, and stimulate inflammatory response

  3. Induration at injection site measured after 2-3 days to determine if test is positive
• Mantoux skin test


  Example of type 4 (delayed) hypersensitivity reaction
• Ziehl-Nielson or Kinyoun stain

  Acid-fast stain that discriminates mycobacteria from other bacteria - mycobacteria retain the red stain after acid wash, while other bacteria are decolourised
• BCG vaccine


  Live attenuated strain of Mycobacterium bovis that stimulates cell-mediated immunity against M. tuberculosis, but does not prevent infection
• On a properly AFB-stained sputum specimen, the acid-fast bacilli will appear red, not gram-negative
• Mycobacterium tuberculosis must be cultured on Lowenstein-Jensen media, not MacConkey plates used for gram-negative enteric organisms
• Tuberculous granuloma


  • Central caseous necrosis surrounded by activated macrophages (epithelioid cells) and T lymphocytes
  • Langhans giant cells (multinucleated cells from fusion of epithelioid cells) may be present
• Caseous necrosis


  Degenerating necrotic macrophages
• Primary or Ghon complex

  First-time TB infection producing granulomatous lesion at lung periphery, together with involvement of regional lymph nodes
• Secondary pulmonary tuberculosis


  TB infection in previously exposed individual, causing extensive granuloma formation and caseation due to type IV hypersensitivity reaction
• Terms for TB in different locations

  • Tuberculosis of lymph nodes = scrofula
  • Tuberculosis of spine = Potts disease
  • Tuberculosis of skin = lupus vulgaris
• Miliary tuberculosis


  Disseminated TB from erosion of a focus into blood or lymphatic vessel, seeding distant organs with minute granulomatous lesions
• Acute tuberculous bronchopneumonia


  Complication of primary or secondary TB due to erosion of a bronchus by enlarging granuloma, causing sudden spread of caseous material into lower lung lobes
• Acid-Fast Bacilli (AFB)


  Mycobacteria that retain the red stain after acid decolourisation, due to their acid-resistant cell wall
• Sputum smear AFB positive vs culture positive

  Sputum smear positive indicates high concentration of organisms (>105/ml) and high infectivity, while culture positive with smear negative indicates low concentration of organisms and lower infectivity
• It takes 6-8 weeks for Mycobacterium tuberculosis to grow in culture
• Sputum AFB positive


  Concentration of organisms in the sputum is high (at least 105 organisms per ml)
• Sputum culture positive


  Concentration of organisms in the sputum is low (too few to be viewed easily on the slide, and too few to be easily transmitted to others when coughing)
• It is possible for the sputum to be AFB negative, but the culture positive
• In most places in the Pacific, TB culture is not routinely done. Diagnosis is made on the basis of the AFB stain of the sputum
• It takes 6-8 weeks for Mycobacterium tuberculosis to grow in the lab and produce a positive culture
• Mantoux test


  1. Tuberculin 0.1 ml (usually 10 IU) is injected intradermally on the volar surface of the forearm

  2. Induration is measured in 48 - 72 hours
• Mantoux test


  Tests for type IV hypersensitivity to Mycobacterium antigens
• A positive Mantoux indicates only TB infection, and can not distinguish active TB disease from latent (dormant) infection
• Finding AFB on a sputum smear is the easiest way to diagnose active pulmonary tuberculosis
• Extra-pulmonary TB is diagnosed by finding AFB on smear from another site (eg CSF in TB meningitis) or seeing AFB or characteristic granulomatous changes on histopathology of tissue (eg a lymph node)
• Extrapulmonary tuberculosis


  Tuberculosis is spread by aerosolisation of organisms, and extrapulmonary TB is unlikely to become aerosolised and infect others
• Someone with a positive Mantoux has about a 10% chance of developing active tuberculosis over the course of their lifetime, OR a 90% of not developing active TB
• If a person is HIV positive, the person has a 10% chance PER YEAR of developing active tuberculosis
• Corticosteroids


  Impair cell-mediated immunity, and permit tuberculous bacilli to reemerge from dormancy, in a reactivation of tuberculous infection
• Adults with active pulmonary TB usually have cavitary lesions, while children do not. Children's coughs tend to be more benign, and it is very unusual for children to spread aerosolised tuberculosis bacilli to other family members