Internal Medicine (Theory) · MU Sofia

9. Pulmonary tuberculosis - primary forms; 10. Pulmonary tuberculosis — secondary forms

Covers the causative organism Mycobacterium tuberculosis and its key features, the granulomatous inflammatory process, and immunity and transmission, then contrasts primary tuberculosis (Ghon focus, lymph node involvement, latency) with secondary reactivation in the upper lobes. Also includes a risk factor table, a symptom table, physical examination, laboratory tests such as Ziehl-Neelsen staining and the Mantoux test, and chest X-ray patterns for the various forms.

Inside: 9 sections · 6 labelled pictures · 2 tables · 15 flashcards · 5 min

Topic 9 of 58 in the MU Sofia syllabus for Internal Medicine (Theory) (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 510 words (5 min of reading), with 15 flashcards.

In this note

  1. Pulmonary tuberculosis – primary forms & Pulmonary TB – secondary forms
  2. Definition
  3. Risk Factors
  4. Primary Tuberculosis
  5. Secondary Tuberculosis
  6. Symptoms of Pulmonary TB
  7. Physical Exam Findings
  8. Lab Investigations
  9. Imaging (Chest X-Ray)

Definition

Pulmonary TB is an infectious disease caused by Mycobacterium tuberculosis. It primarily affects the lungs, but may also involve the bones, joints, kidneys, peritoneum, and genital system.

M. tuberculosis: Key Features

  • Obligate aerobes → prefer oxygen-rich areas like the lungs.
  • Intracellular pathogens → survive inside macrophages; explains the strong T-cell immune response and lymphocyte increase in patients.
  • Acid-fast bacilli → stainable with Ziehl-Neelsen stain for diagnosis.

TB Inflammatory Process: Special Characteristics

  • Tubercles → small granulomas formed of epithelioid cells, Langhans giant cells, and lymphocytes.
  • Caseous necrosis → cheese-like central necrosis, may liquefy to form cavitation.
  • Calcification during healing → common feature as lesions resolve.

Immunity in TB

  • T-cell mediated immunity → crucial in defense.
  • Natural immunity = asymptomatic carriers.
  • Artificial immunity = BCG vaccination (contains attenuated tuberculous bacteria, which act only as an Ag w/out causing a disease.)
  • Transmission: via inhalation of droplets containing M. tuberculosis.

Primary Tuberculosis

  • Occurs shortly after initial exposure to TB bacilli.
  • Affects middle & lower lobes (site of maximum air distribution).
  • Develops Ghon focus (acute exudative lesion) → may spread to regional lymph nodes.
  • Hilar or paratracheal lymphadenopathy appears.
  • Caseation & calcification of lymph nodes commonly follow.
  • The nonspecific inflammatory response evoked on 1st exposure to tubercle bacilli becomes granulomatous, evoking the formation of tubercles.
  • Ghon complex = combo of Ghon focus (lung lesion) + nearby lymph node swelling ± pleural thickening.
  • TB bacteria can silently spread through blood (hematogenous dissemination) to other body parts.
  • After body develops immunity, TB usually becomes latent (silent) in most people (90%) with no symptoms.
  • In young kids or weak immune systems, TB may progress—either at the lung or other body sites reached early.

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