Tuberculosis

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TB Pathophysiology - The Ghon Show

  • Primary TB: Occurs on first exposure. Organisms implant in subpleural airspaces of the mid-to-lower lobes.
  • Pathogenesis: Mediated by Th1 cells activating macrophages via IFN-γ. Activated macrophages form epithelioid histiocytes and Langhans giant cells, leading to caseating necrosis.
  • Ghon Focus: The initial parenchymal granuloma.
  • Ghon Complex: Ghon focus + associated hilar lymph node granuloma. Usually contains the infection in immunocompetent hosts.

⭐ A Ghon complex that has undergone subsequent fibrosis and calcification is known as a Ranke complex, indicating healed primary TB.

TB Clinical Forms - Consumption's Comeback

  • Primary TB: Usually asymptomatic. Ghon complex (calcified lung focus + hilar node) → Ranke complex.
  • Latent TB (LTBI): Contained, non-infectious. Positive TST/IGRA, negative CXR, no symptoms.
  • Reactivation (Secondary) TB: Symptomatic disease from LTBI, often in immunosuppressed (HIV, TNF-α inhibitors).
    • Symptoms: "Consumption" (fever, night sweats, weight loss), cough, hemoptysis.
    • Location: Apical/posterior upper lobes (high O₂).
  • Extrapulmonary/Miliary:
    • Pott's Disease: Vertebral body destruction.
    • Scrofula: Cervical lymphadenitis.
    • Miliary: Hematogenous spread; "millet-seed" CXR.

⭐ Reactivation TB classically presents with cavitary lesions in the lung apices, a high-oxygen environment where M. tuberculosis thrives.

TB Diagnosis - Spotting the Intruder

  • Latent TB Screening:

    • Tuberculin Skin Test (TST/PPD): Positive if induration is:
      • ≥5 mm: HIV+, recent contacts, fibrotic changes on CXR.
      • ≥10 mm: Recent immigrants, IVDU, high-risk settings.
      • ≥15 mm: No known risk factors.
    • Interferon-Gamma Release Assays (IGRAs): Blood test, preferred if BCG vaccinated.
  • Active TB Diagnosis:

    • Sputum Analysis: 3 samples; AFB smear (Ziehl-Neelsen), NAAT, and culture (gold standard).
    • Chest X-ray: Look for upper lobe cavitations, Ghon complex, or miliary pattern.

High-Yield: IGRAs (like QuantiFERON-Gold) are more specific than TST in patients who have received the BCG vaccine, avoiding false-positive results.

TB Treatment - RIPE for the Picking

📌 RIPE Mnemonic for standard 6-month regimen.

  • Rifampin: Red-orange body fluids (tears, urine); potent CYP450 inducer.
  • Isoniazid (INH): Peripheral neuropathy, hepatotoxicity. Requires B6.
  • Pyrazinamide (PZA): Hyperuricemia (can precipitate gout), hepatotoxicity.
  • Ethambutol: Eye issues (optic neuritis, red-green color blindness).

⭐ Always co-administer Pyridoxine (Vitamin B6) with Isoniazid to prevent peripheral neuropathy.

High‑Yield Points - ⚡ Biggest Takeaways

  • Primary TB is often asymptomatic, forming a Ghon complex; reactivation classically occurs in the lung apices.
  • Suspect extrapulmonary TB in vertebral pain (Pott's disease) or cervical lymphadenitis (scrofula).
  • Screen for latent TB with PPD or IGRA; diagnose active disease with sputum AFB smear and culture.
  • Standard therapy for active TB is RIPE: Rifampin, Isoniazid, Pyrazinamide, Ethambutol.
  • Key side effects: Isoniazid causes hepatotoxicity and neuropathy (give B6); Ethambutol causes optic neuritis.

Practice Questions: Tuberculosis

Test your understanding with these related questions

A 24-year-old man comes to the physician for a routine health maintenance examination. He feels well. He has type 1 diabetes mellitus. His only medication is insulin. He immigrated from Nepal 2 weeks ago . He lives in a shelter. He has smoked one pack of cigarettes daily for the past 5 years. He has not received any routine childhood vaccinations. The patient appears healthy and well nourished. He is 172 cm (5 ft 8 in) tall and weighs 68 kg (150 lb); BMI is 23 kg/m2. His temperature is 36.8°C (98.2°F), pulse is 72/min, and blood pressure is 123/82 mm Hg. Examination shows a healed scar over his right femur. The remainder of the examination shows no abnormalities. A purified protein derivative (PPD) skin test is performed. Three days later, an induration of 13 mm is noted. Which of the following is the most appropriate initial step in the management of this patient?

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Flashcards: Tuberculosis

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Conditions that cause _____ include infection, medication, vestibular dysfunction, and chemoradiation

TAP TO REVEAL ANSWER

Conditions that cause _____ include infection, medication, vestibular dysfunction, and chemoradiation

vomiting

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