Clinical Case Studies - TB

Question 1

What is Tuberculosis?

Answer 1

TB is defined as a granulomatous disease caused by members of the M. tuberculosis complex (acid-fast bacillus)

Question 2

Describe the microbiological features of Mycobacterium tuberculosis

Answer 2

• Cell envelope — core of three macromolecules covalently linked. Outermost layer consists of a lipid bilayer structure
• Staining characteristics — Stains positive with Gram stain. The mycolic acid structure confers the ability to resist destaining by acid alcohol “acid-fast bacillus (AFB)”
• Growth characteristics — Slow

Question 3

What are the potential disease outcomes of TB?

Answer 3

• Immediate clearance of the organism
• Primary disease: immediate onset of active disease
• Latent infection
• Reactivation disease: onset of active disease many years following a period of latent infection (immunosuppressed individuals)

Question 4

What is the pathophysiology of primary TB disease of the lung?

Answer 4

• Established infection in the lungs via aerosol droplets
• Bacilli proliferate inside alveolar macrophages
• Cytokines and chemokines attract phagocytic cells and form a nodular granulomatous structure called a Ghon focus
• Lymphadenopathy + above = Ghon complex. When calcified = Ranke complex
• Immunocompetent patients - caseous necrosis - latency due to lowered O2 and pH levels
• Immunosuppressed patients - liquefaction of necrotic tissue - coughing of infected liquid from bronchus

Question 5

What tests can but used to identify TB?

Answer 5

Tissue Samples

Sputum

Transbronchial biopsy - granulomas are diagnostic

Pleural fluid aspirates

Microbiologic Testing

Sputum AFB smear - Ziehl-Neelsen or Kinyoun method vs flurochrome procedure

Mycobacterial culture - Egg based (Lowenstein-Jensen), Agar based (Middlebrook 7H10 or 7H11)

NAA testing — Nucleic acid amplification (NAA) tests

Radiographic Imaging

CXR - Ghon Focuses. Unilateral or bilateral. Cavitation. Enlargement of hilar and mediastinal lymph nodes.

CT - Less often used, can show early disease. May be used when alternative diagnosis is suspected

Question 6

What are the signs and symptoms of TB?

Answer 6

SYMPTOMS:

• Cough
• Fever
• Weight loss
• Chest pain
• Dyspnea

SIGNS:

• Crackles
• *

Question 7

Asides from the lung, what other forms of TB are there?

Answer 7

• Miliary (haematogenous dissemination of Mycobacterium tuberculosis)
• Genitourinary
• Bone (Pott’s disease of the spine)
• Peritoneal
• Meningitis

Question 8

What is the treatment of TB?

Answer 8

RIPE

• Rifampicin
• Isoniazid
• Pyrazinamide
• Ethambutol