Mycobacterium tuberculosis

• Mycobacterium tuberculosis causes tuberculosis
• Most commonly pulmonary TB but extrapulmonary tuberculosis is possible (including adenitis, gastrointestinal TB, pericarditis, meningitis)
• Standard treatment for susceptible TB is RIPE x2mo then RI x4mo

Classification

• Primary vs. reactivation vs. reinfection
• Latent vs. active

Epidemiology

• Reinfection accounts for ~40% of active tuberculosis in endemic countries
• Latent tuberculosis in ~30% of the global population

Clinical Presentation

• Primary tuberculosis is usually asymptomatic
  • Possible presentations include mild URTI with cough and/or fever
  • May be seen on CXR as infiltrate in mid-lung zones with hilar adenopathy
    • Ghon complex, especially in children
  • May progress in children and the immunocompromised patients
• Recent primary tuberculosis
  • Immunological phenomena
    • Erythema nodosum
    • Phlyctenular conjunctivitis
• Recent or active tuberculosis
  • Erythema induratum
• Reactivation tuberculosis
  • Poorly-defined clinical course
  • Usually reactivates in lung apices
• Active tuberculosis
  • Cough and fever for more than two weeks
  • Cough and HIV infection
• Extra-pulmonary tuberculosis
  • Pleural tuberculosis is most common
  • Scrofula (cervical lymph node infection) next-most common
  • Tuberculous meningitis
  • Tuberculous pericarditis
  • Renal tuberculosis
  • Abdominal tuberculosis
  • Gastrointestinal tuberculosis

Investigations

• AM sputum for acid-fast bacilli x3
  • About 70% sensitive
• ANTB (PCR)
  • About 75% sensitive

Management

• Standard HREZ x2mo then HR x4mo
  • Isoniazid 5mg/kg/d, max 300mg daily
  • Rifampin 10mg/kg/d
  • Pyrazinamide 25mg/kg/d, max 2g daily
  • Ethambutol 20mg/kg/d, max 1.2g daily
  • Pyridoxine
• Airborne precautions until:
  • Treated for at least 2 weeks
  • 3x negative sputum smears
    • Collected at 8- to 24-hour intervals, including one early morning collection
  • Improvement in symptoms

DILI

• Most common complication leading to treatment interruption, with a mortality of 6-12% if drugs are not stopped
• Rif > INH > PZA
• Most patients can have the same TB drugs reintroduced without recurrence of DILI, though recurrence can be delayed
• Procedure
  • Hold if ALT >120 and symptoms, if ALT >200 even without symptoms, or bili >2x ULN
  • Switch to second-line meds
  • Reintroduce the original drugs once AST & ALT are <2x ULN
  • Only rechallenge with pyrazinamide if it was a mild case

Adherence to Treatment

• Refer to Let's Talk TB

Further Reading

• Tuberculosis Standards, 7th Edition (2014)