Tuberculosis Lecture Notes

Overview

• Topic: Tuberculosis (TB)
• Key Areas Covered:
  • Pathophysiology
  • Pulmonary and Extrapulmonary TB
  • Diagnostic Steps
  • Treatment for Latent and Active TB

Pathophysiology

• Causative Agent: Mycobacterium tuberculosis (Airborne pathogen)
• Pathogenesis:
  • Inhalation into respiratory tract
  • Invades the lungs, especially the right middle and lower lobes
  • Immune response triggers macrophages, which phagocytose the bacterium
  • TB inhibits phagolysosome fusion inside macrophages, allowing it to proliferate
  • Formation of granulomas with caseous necrosis (central necrosis), surrounded by macrophages and T lymphocytes
  • Specific Granuloma: Ghon Focus in the middle/lower lobes close to the pleura
  • Spread to lymph nodes causing hilar lymphadenopathy; together forming Ghon Complex indicating primary TB
  • T cells release Interferon-gamma to recruit more macrophages and form granulomas

High-Risk Populations

• Exposure Risk:
  • Prisons
  • Health Care Workers
  • Homeless
  • Immigrants
  • IV Drug Abusers
• Progression Risk:
  • HIV patients
  • Status post transplant recipients
  • Patients on immunosuppressants
  • Elderly
  • Malnourished individuals
  • Diabetics, CKD patients, Alcoholics

Disease Progression

• Latent TB (90% of cases):
  • Pathogen goes dormant with fibrocystic changes (Ranke Complex if fibrocystic)
  • No symptoms, contained by the immune system
• Active TB:
  • Primary Progressive TB (<10% of cases)
  • Secondary TB (Reactivation from latent phase)
  • Reactivates particularly in upper lobes causing fibrocaseous necrosis

Complications of Pulmonary TB

• Fibrocavitatory lesions
• Pneumothorax (air leakage in pleural cavity)
• Bronchopneumonia
• Pleural effusion
• Hemoptysis (coughing up blood)
• Symptoms: night sweats, fever, weight loss, cough

Extrapulmonary TB (Miliary TB)

• Spread via bloodstream to other organs:
  • Meningitis (TB meningitis)
  • Cervical lymph nodes (Scrofula)
  • Pericarditis (constrictive)
  • Hepatitis
  • Pyuria (sterile pyuria in kidneys)
  • Addison's disease (Adrenals)
  • Pott's disease (vertebrae)
  • Osteomyelitis (long bones)

Diagnostics

• Initial Screening:
  • PPD (Tuberculin Skin Test, Mantoux Test)
  • Positive results vary by population (5mm, 10mm, 15mm thresholds)
  • False positives in BCG vaccinated; False negatives in immunocompromised
  • Interferon Gamma Release Assay recommended for better specificity
• Imaging:
  • Chest X-ray/CT for confirming active disease
  • Positive signs: Upper lobe fibrocavitatory lesions, Consolidation, Miliary TB indications
• Confirmatory Test:
  • Sputum culture (three samples, >8 hours apart)
  • Acid Fast Bacillus Smear and Culture (Gold Standard)
  • Biopsy for caseating granulomas (if performing bronchoscopy)

Treatment

• Latent TB:
  • Isoniazid (INH) + Vitamin B6 for 9 months OR
  • Rifampin for 4 months
  • Consider DOT for compliance
• Active TB:
  • R-I-P-E regimen for 2 months
    • Rifampin, Isoniazid, Pyrazinamide, Ethambutol (or Streptomycin)
  • Followed by Rifampin + Isoniazid for 4 more months
  • Monitor for drug compliance (DOT for active TB)

Drug Side Effects

• Rifampin:
  • Red-orange urine, tears
  • CYP450 inducer (caution with HIV meds)
• Isoniazid (INH):
  • B6 deficiency: neuropathy, seizures
  • Hepatotoxicity: monitor LFTs
• Pyrazinamide:
  • Hyperuricemia (gout)
  • Hepatotoxicity: monitor LFTs
• Ethambutol:
  • Optic neuritis: vision changes, requires eye exams
• Streptomycin:
  • Nephrotoxicity: monitor renal function
  • Ototoxicity: hearing loss

Case Study Example

• 45-year-old male, homeless, history of HIV and IV drug abuse
• Presented with night sweats, weight loss, hemoptysis
• Diagnosed with active TB based on positive PPD, chest X-ray, and sputum cultures
• Treated with R-I-P-E regimen for 6 months

End of notes.