Are the terms extrinsic (allergic) and intrinsic (non-allergic) asthma still used in current clinical practice?

Extrinsic and Intrinsic Asthma Classification: Current Status in Clinical Practice

The terms "extrinsic" (allergic) and "intrinsic" (non-allergic) asthma are outdated and should no longer be used in current clinical practice. Instead, asthma is now classified based on phenotypes, endotypes, and assessment of control and severity 1, 2.

Historical Context and Evolution of Terminology

• The terminology of "extrinsic" and "intrinsic" asthma was first introduced by Rackeman in 1947, with extrinsic referring to allergen-triggered asthma and intrinsic referring to non-allergic asthma with unknown triggers 2.
• Historically, extrinsic asthma was characterized by positive skin tests to aeroallergens, while intrinsic asthma showed negative skin tests 3, 2.
• These terms were commonly used through the 1990s, with "extrinsic-allergic asthma" being recognized as affecting the majority of asthma patients who demonstrated sensitization to inhaled or food allergens 4.

Current Classification Approach

• Modern asthma guidelines have moved away from the extrinsic/intrinsic dichotomy toward a more comprehensive understanding of asthma as a heterogeneous condition with multiple phenotypes and endotypes 5, 1.
• Current classification focuses on:
  • Level of control (controlled, partly controlled, uncontrolled) 6
  • Severity (intermittent, mild persistent, moderate persistent, severe persistent) 1
  • Specific phenotypes (allergic, non-allergic, occupational, aspirin-exacerbated respiratory disease, exercise-induced, cough variant) 1

Why the Terminology Changed

• The recognition that asthma is not a single disease but a heterogeneous condition with various underlying pathophysiological mechanisms led to this shift 5.
• The four components of asthma (symptoms, airway obstruction, airway hyperresponsiveness, and airway inflammation) are only loosely associated, making simple dichotomous classification inadequate 5.
• Research has shown that asthma control should encompass both the patient's current clinical state and future risk of adverse outcomes, which is not captured by the extrinsic/intrinsic classification 5.

Current Understanding of Asthma Pathophysiology

• Asthma is now understood as involving chronic inflammation with activation of various immune cells including mast cells, eosinophils, T lymphocytes, and epithelial cells 7.
• The underlying mechanisms include:
  • Airway inflammation (the fundamental process)
  • Bronchoconstriction
  • Airway hyperresponsiveness
  • Airway edema
  • Airway remodeling 7

Clinical Implications

• The shift from extrinsic/intrinsic classification to phenotype-based approaches has important implications for treatment decisions 6, 1.
• Treatment is now guided by:
  • Assessment of current control
  • Evaluation of future risk factors
  • Identification of specific phenotypes that may respond to targeted therapies 5
• This approach allows for more personalized treatment strategies that address the specific underlying mechanisms in each patient 7, 6.

Diagnostic Approach in Modern Practice

• Current diagnosis focuses on:
  • Establishing the presence of variable airflow limitation
  • Documenting airway hyperresponsiveness
  • Identifying specific triggers and inflammatory patterns 5
• Allergic status is still assessed but is considered one component of a broader phenotypic characterization rather than a defining feature 1, 2.

The evolution from the extrinsic/intrinsic dichotomy to the current multidimensional approach reflects our improved understanding of asthma's complex pathophysiology and heterogeneity, allowing for more targeted and effective management strategies 5, 6.