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Updated: Apr 13 2022

Pulmonary Tuberculosis and PPD

Images tb.jpg complex tb.jpg tb.jpg
  • Snapshot
    • A 37-year-old man presents to his primary care physician with subjective fever, malaise, and cough. He reports a few episodes of night sweats and has noted an unintentional 15-pound loss over the course of 2 months. Yesterday, he noted bloody sputum. He recently immigrated from Central Africa and currently lives with many family members in a small apartment. Chest radiograph demonstrates a cavitary lesion in the right upper lobe of the lung.
  • Introduction
    • Definition
      • infection of the respiratory system caused by Mycobacterium tuberculosis
    • Transmission
      • inhaling airborne particles (droplet nuclei)
      • suspected patients should be placed on respiratory isolation precautions during workup
    • Extrapulmonary Tb
      • meningitis
      • Pott disease (vertebral infection)
      • miliary Tb
      • pericarditis
      • adrenal gland infection
      • genitourinary Tb
  • Epidemiology
    • Risk factors
      • close contact with someone with tuberculosis (Tb)
        • e.g., prisons and homeless shelters
      • immigrating from highly endemic regions such as
        • Bangladesh
        • Cambodia
        • Central African Republic
      • working in hospitals and nursing homes
      • immunosuppression (e.g., HIV, diabetes, and on immunosuppressive medications)
      • substance use disorder
        • most important for diffuse reticulonodular pattern
  • Etiology
    • Pathophysiology
      • droplet nuclei produced by coughing gets inhaled → recruits macrophages when in the alveoli → dissemination of macrophage infected cells into deeper tissues and caseating granuloma formation
    • Mycobacterium tuberculosis
  • Presentation
    • Symptoms
      • cough (productive or nonproductive)
      • hemoptysis
      • night sweats
      • fever
      • loss of appetite
    • Physical exam
      • weight loss
      • although physical exam is not helpful in diagnosing Tb, it is important to assess for extrapulmonary involvement
        • e.g., hepatosplenomegaly, lymphadenopathy, scrotal, and pelvic tenderness
  • Imaging
    • Chest radiography
      • findings
        • non-specific findings (e.g., patchy or lobar consolidation or non-detectable lesions)
        • cavitary lesions
        • miliary nodules
        • hilar adenopathy
        • pleural effusion
  • Studies
    • Sputum specimen
      • acid-fast bacilli
      • culture
      • nucleic acid amplification tests
    • Blood
      • interferon-gamma release assay
    • Tuberculin skin test
      • results in a delayed immune response with the administration of purified protein derivatives (PPD) from Mycoplasma tuberculosis
        • measured in 48-72 hours
      • Findings
        • ≥ 5 mm
          • considered a positive test in patients with
            • HIV
            • recent Tb exposure
            • chest radiographic findings consisted of healed Tb infection
            • organ transplantation or on immunosuppressants
        • ≥ 10 mm
          • considered a positive test in patients with
            • injection drug users
            • chronic diabetes
            • chronic renal failure
            • employees in high-risk settings (e.g., physicians, nurses, or prison workers)
            • recent immigrant from endemic country
        • ≥ 15 mm
          • considered a positive test in patients with no known risk factors
  • Treatment
    • Medical
      • rifampin, isoniazid, pyrazinamide, and ethambutol (RIPE) therapy
        • indication
          • treatment of choice for the 2-month initial phase
            • 4-month continuation phase is with rifampin and isoniazid
        • side effects
          • isoniazid should be given with vitamin B6 (pyridoxine) to prevent peripheral neuropathy
            • B6 deficiency can cause refractory seizures
              • treat with pyridoxine
          • rifampin, isoniazid, and pyrazinamide can cause liver toxicity
          • ethambutol results in optic neuropathy
          • rifampin causes reddish-orange discoloration of body secretions
          • pyrazinamide causes hyperuricemia, which can precipitate gouty attacks 
      • isoniazid
        • indication
          • for Tb prophylaxis
  • Complications
    • Tuberculoma
    • Aspergilloma
    • Acute respiratory failure
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