9- TB overview

• Inhalation of aerosol droplets containing M. tuberculosis

  1. Deposition in the lungs

  2. One of four possible outcomes:
• Possible outcomes of M. tuberculosis infection

  • Immediate clearance of the organism (no infection)
  • Primary disease: immediate onset of active disease
  • Latent infection: infected by Tb but infection is contained by the immune system & the patient develops cell-medicated immunity
  • Reactivation disease: onset of active disease many years following a period of latent infection
• Primary Tb


  Initial infection with Mycobacterium tuberculosis
• Primary Tb

  • Mostly asymptomatic; may present as erythema nodosum, pleural effusion, or collapse (if compressed by enlarged LNs)
  • Upper region of lungs
  • Ghon focus: granulomatous lesions: central areas of caseation surrounded by epithelioid & giant Langerhans cells. subpleural lesion
  • Ghon complex: Ghon focus + caseous lesions in mediastinal & cervical LNs
  • The majority heal and calcify à Latent infection. May reactivate in the future.
• Reactivation Tb

  Only 5-10% of people with primary Tb get active disease in their life, they get it if immunosuppressed
• Causes of Reactivation Tb

  • HIV co-infection
  • Chemotherapy, steroids, cytotoxins
  • DM, ESKD, lymphoma
  • Malnutrition, aging
• Active Tb

  • Fever, night sweats, weight loss
  • Cough: dry>> purulent (mucoid purulent or blood stained) >> hemoptysis
  • Apical areas
• Extrapulmonary Tb sites


  • LNs
  • primary TB can be in GI: ILEOCECAL REGION (like Crohn's)
  • Pleura, GU, spine, kidneys, meninges
  • LNs: firm nontender enlargement, centrally necrotic, overlying skin may be indurated or have sinus tract formation
  • Tuberculous meningitis
  • Choroidal tubercles (yellow/ white raised lesions) in eyes
  • Hepatosplenomegaly (in later stages)
• Miliary Tb

  • Hematogenous dissemination; characterized by the presence of small, firm 1-2mm white nodules
  • Mostly in lungs, LNs, bones, CNS (detect with MRI), liver/spleen