What are the different types of tuberculosis (TB)?

Types of Tuberculosis: Pulmonary and Extrapulmonary

Tuberculosis (TB) is classified into two main types: pulmonary tuberculosis and extrapulmonary tuberculosis, based on the location of infection in the body.

Pulmonary Tuberculosis

Pulmonary TB is the most common form of tuberculosis, affecting the lungs. It is further classified into:

1. Primary Pulmonary TB:

   • Represents the first infection with Mycobacterium tuberculosis
   • Usually occurs in the mid-lung zones
   • Often asymptomatic
   • Characterized by a parenchymal focus and satellite lymphadenopathy
   • More common in children 1

2. Post-primary (Reactivation) Pulmonary TB:

   • Typically affects the upper lobes of the lungs
   • Can result from:
     • Reactivation of a dormant focus formed during primary infection
     • New exogenous reinfection
   • More common in adults 1

Extrapulmonary Tuberculosis

Extrapulmonary TB involves organs other than the lungs and accounts for a significant proportion of TB cases worldwide 2. Common forms include:

1. Miliary TB: Widespread dissemination affecting multiple organs 1

2. Tuberculous Meningitis: Affects the base of the skull with clear cerebrospinal fluid showing hypoglycorrhachia and lymphocyte pleocytosis 1

3. Lymph Node TB (Tuberculous Lymphadenitis):

   • Most commonly affects cervical lymph nodes
   • Usually unilateral 1

4. Pleural TB: Can be exudative or dry 1

5. Other Serositis Forms:

   • Tuberculous pericarditis
   • Tuberculous peritonitis 1

6. Skeletal TB:

   • Spinal TB (Pott's disease) - typically affects lower thoracic vertebrae
   • Tuberculous osteoarthritis 1

7. Genitourinary TB:

   • Renal TB affecting the medullary region
   • Genital tract TB 1

8. Gastrointestinal TB: Commonly affects the ileocecal region 1

9. ENT Tuberculosis:

   • Laryngeal TB
   • Tuberculous otitis media
   • Nasal TB 3

Classification Based on Host-Parasite Relationship

The American Thoracic Society and CDC provide a classification system based on exposure, infection, and disease status 4:

1. No TB exposure, not infected: No history of exposure and negative tuberculin skin test

2. TB exposure, no evidence of infection: History of exposure but negative tuberculin skin test

3. Latent TB infection, no disease: Positive tuberculin skin test but no clinical, bacteriological, or radiographic evidence of active TB

4. TB, clinically active: Clinical, bacteriological, and/or radiographic evidence of current TB

5. TB, not clinically active: History of previous TB or abnormal stable radiographic findings with positive tuberculin test but no current evidence of disease

6. TB suspect: Diagnosis pending

Diagnostic Considerations

Diagnosis of TB varies depending on the type:

• Pulmonary TB: Diagnosed through sputum microscopy, culture, and molecular tests like GeneXpert 4

• Extrapulmonary TB: Often requires tissue sampling and histopathological examination; diagnosis can be challenging due to:

  • Insidious clinical presentation
  • Poor performance of diagnostic tests
  • Technical constraints in obtaining adequate samples 2

Treatment Approach

Treatment regimens are determined by the category of TB 4:

• Category I (New smear-positive pulmonary TB, severe forms of extrapulmonary TB): 2HRZE followed by 4HR

• Category II (Relapse, treatment failure): 2HRZES/1HRZE followed by 5HRE

• Category III (Less severe forms of extrapulmonary TB): 2HRZ followed by 4HR

Where H=isoniazid, R=rifampin, Z=pyrazinamide, E=ethambutol, S=streptomycin

Special Considerations

• HIV Co-infection: Extrapulmonary TB is more common in HIV-infected individuals and is considered a diagnostic criterion for AIDS 5

• Immunocompromised Patients: Higher risk for extrapulmonary TB and may require longer treatment durations 5

• Children: Primary TB is more common; extrapulmonary manifestations may be more frequent 4

Clinical Pearls

• A high index of suspicion is needed for extrapulmonary TB as symptoms can be nonspecific and insidious 5

• Negative tuberculin skin tests do not exclude TB diagnosis, especially in immunocompromised patients 5

• All cases of TB must be reported to local health departments to facilitate contact tracing and public health interventions 4

• TB in a child is a "sentinel event" suggesting recent transmission, often from a family member 4

Understanding the different types of TB is crucial for appropriate diagnosis, treatment, and public health management of this infectious disease.