Please confirm topic selection

Are you sure you want to trigger topic in your Anconeus AI algorithm?

Please confirm action

You are done for today with this topic.

Would you like to start learning session with this topic items scheduled for future?

Updated: Aug 14 2020

Mycobacterium Tuberculosis

  • Snapshot
    • A 33-year-old man presents to his primary care physician for a cough and generalized malaise. His symptoms are associated with 2 episodes of mild hemoptysis and night sweats. He denies any sick contacts or recent travels; however, he states he was released from prison 4 months ago. Physical examination is unremarkable. A chest radiograph is obtained, which demonstrates pulmonary infiltrates and cavitations in the upper lobe.
  • Introduction
    • Classification
      • acid-fast, rod-shaped, obligate aerobic, intracellular bacteria
    • Epidemiology
      • risk factors
        • traveling to endemic areas (e.g., Angola and the Central African Republic)
        • close contact (e.g., prisons, nursing homes, homeless shelters, and hospitals)
        • immunocompromised (e.g., HIV, immunosuppressive medications, and diabetes)
    • Transmission
      • airborne spread of droplet nuclei from patients with infectious tuberculosis (TB)
    • Microbiology
      • acid-fast on Ziehl-Neelsen staining
      • immune system itself causes damage
        • TB contains no endotoxins or exotoxins
      • cord factor
        • inhibits leukocyte migration
        • causes characteristic serpentine growth pattern
        • induces TNF-α release
      • tuberculin
        • triggers cell-mediated immunity → caseation and granulomas
        • triggers delayed hypersensitivity reaction
        • a surface protein
      • sulfatides
        • prevent phagosome-lysosome fusion
    • Pathogenesis
      • the infected person coughs up small droplets containing the bacteria that reaches the terminal alveoli of the uninfected person
        • alveolar macrophages are recruited, which eventually become infected, transporting the microbe to deeper tissues
        • more alveolar macrophages are recruited, leading to granuloma formation
          • granulomas are formed to "wall off" TB, where it lies dormant
      • secondary TB occurs when the patient's immune system is weakened (e.g., newly acquired HIV infection, being on immunosuppressant medications, malignancy, and poor nutrition)
        • macrophages' ability to maintain their barrier decreases, facilitating possible dissemination
        • TB infection typically manifests in the apical/posterior segments of the lung due to its increased oxygen tension
  • Presentation
    • TB can lead to pulmonary and extrapulmonary manifestations
      • lymph nodes (tuberculous lymphadenitis)
      • pleura
      • genitourinary
      • skeleton (can lead to Pott disease with spinal involvement)
      • meninges
      • gastrointestinal system
      • pericardium (tuberculous pericarditis)
    • Symptoms
      • typically asymptomatic in primary TB
      • cough
      • hemoptysis
      • fever
      • night sweats
      • malaise
    • Physical exam
      • weight loss
      • lymphadenopathy
      • dullness to percussion or decreased/absent breath sounds if there is a pleural effusion
      • back pain in spinal TB (Pott disease)
  • Imaging
    • Chest radiograph
      • indication
        • initial imaging study in the evaluation of TB
      • findings
        • middle or lower lung infiltrate (suggestive of primary infection)
        • upper lobe infiltrate (suggestive of latent TB reactivation)
          • apices have higher oxygen tension and reduced perfusion/lymph clearance compared to the base
        • cavitary lesions
        • Ghon complex (lobar or perihilar lymph node involvement)
  • Studies
    • Sputum acid-fast testing
      • demonstrates acid-fast bacilli
    • Real-time nucleic acid amplification
      • rapidly confirms TB and is considered the first-line diagnostic study
    • Tuberculin skin test (TST)
      • most widely used to screen for latent TB infection
      • a delayed-type hypersensitivity reaction against purified protein derivative (PPD) is induced
        • the size of the induration is assessed after 48-72 hours
        • note, patients who received the Bacille Calmette-Guerin (BCG) vaccination will have false positive results
        • a false negative result can be seen in immunocompromised patients
      • interpretation (positive results)
        • ≥ 15 mm in patients with no risk factors
        • ≥ 10 mm in patients with risk factors (e.g., healthcare worker, traveling to endemic areas, and being in prison)
        • ≥ 5 mm in immunocompromised patients (e.g., HIV, on immunosuppressants, and organ transplant recipients)
        • positive tests require a chest radiograph
    • Interferon-γ release assay
      • measures interferon levels released by the patient's immune system in response to TB antigens
        • the results are not affected by previous BCG vaccination
  • Differential
    • Lung cancer
      • differentiating factor
        • patients will not have positive TB studies
  • Treatment
    • Medical
      • rifampin, isoniazid, pyrazinamide, and ethambutol therapy
        • indication
          • first-line treatment for active pulmonary TB infection for 4 months
            • after 4 months, treatment involves isoniazid and rifampin
        • comments
          • isoniazid can cause peripheral neuropathy as well as sideroblastic anemia due to vitamin B6 deficiency, thus warranting pyridoxine in hopes to prevent this development from occurring
            • can also cause hepatitis
          • ethambutol can cause optic neuropathy
          • mutations in RNA polymerase lead to rifampin resistance
      • isoniazid monotherapy
        • indication
          • prophylactic treatment for latent primary TB after active TB has been excluded
  • Complications
    • Pott disease
    • Miliary or disseminated TB
    • Meningitis
    • Pericarditis
    • Lymphadenitis
    • Adrenal insufficiency
1 of 0
1 of 14
Private Note

Attach Treatment Poll
Treatment poll is required to gain more useful feedback from members.
Please enter Question Text
Please enter at least 2 unique options
Please enter at least 2 unique options
Please enter at least 2 unique options