occ asthma

Diagnosis of Asthma

  • Key Challenges:

    • Securing an accurate diagnosis of asthma for patients or workers.
    • Determining whether it is work-related asthma.

  • Diagnostic Process:

    • Clinical and Occupational History: Essential for establishing a diagnosis.
    • Spirometry:
    • Performed with a Beta-agonist bronchodilator for pre and post-bronchodilator testing.
    • Can provide straightforward diagnosis with appropriate symptoms and examination findings.
    • Methacholine Challenge Testing:
    • Serves as an important adjunctive test to identify reactive airways.
    • Reports up to a 6-30% false positivity rate depending on the study.

  • Additional Testing for Occupational Asthma:

    • Pre and Post Shift Pulmonary Function Tests (PFTs):
    • Assess lung function before and after work at different times of the week.
    • Look for changes in airway reactivity related to workplace exposure.
    • Specific Inhalational Challenge Testing:
    • Optional adjunct but helpful to confirm diagnosis.

Criteria for Diagnosis of Occupational Asthma

  • Medical and Occupational History:
    • Must document specific occupational exposure rather than general work exposure.
  • Agent Identification:
    • Define a specific agent related to bronchial reactivity.
    • Reference literature to support the agent’s classification as an asthmatogen.
  • Hyperresponsiveness Documentation:
    • Evidence of airway hyperresponsiveness post-exposure.
    • Record sensitization status if the agent is immunological.
  • Response Documentation:
    • Record obstructive changes before and after work exposure during the workweek.

Types of Allergic Reactions

  • Immediate Reactions:

    • Occur typically within 15-30 minutes post-exposure.
    • Typically an IgE mediated response.

  • Delayed Responses:

    • Concern over potential for serious outcomes.
    • Can drop off over hours or even days.
    • May lead to exacerbated symptoms after weekends away from exposure.

  • Combined Responses:

    • Patients may exhibit both immediate and delayed reactions.

Risk Factors for Development of Occupational Asthma

  • History of Allergies:
    • Increased risk for individuals with prior allergic histories.
  • Other Factors:
    • Tobacco smoke (weaker trigger).
    • Atopic history (eczema, hives).
    • Family history of asthma or allergies.
    • Higher respiratory demands seen in athletes leading to increased airway sensitivity.

Agents of Exposure

  • Variability of Agents:
    • Agent-specific dose-response relationship with potential for sensitization over time.
  • Occupational Groups at Higher Risk:
    • Laboratory and animal technicians (41% symptom prevalence; 11-30% allergy prevalence).
    • Workers exposed to wheat flour (upwards of 25%).
    • Exposure to red cedars and isocyanates are critical.
    • Increased latex allergies related to glove usage during the HIV epidemic.

Characteristics of Allergens

  • Typical Patterns:
    • Commonly large complex proteins lead to sensitization.
    • Metals (nickel, platinum) recognized allergens.
    • Smaller organic solvents and aerosolized agents also significant.
  • Dose-Response Relationships:
    • Established especially in sensitizing agents.
    • Individual susceptibility varies; some easily sensitized while others remain unaffected.

Recovery from Occupational Exposure

  • Clinical Observations:
    • Symptoms often improve post-removal from exposure.
    • Tables document agents and associated occupational exposures.

Key Agents Causing Occupational Asthma

  1. Animal-based Agents:
    • Substantial prevalence in laboratory settings, handling of various animals (e.g., rodents, birds).
  2. Chemical-Based Antigens:
    • Metals and organic chemicals noted for potential to induce asthma.
  3. Pharmaceuticals:
    • Including those in supplement industries.

Focus on Isocyanates

  • Isocyanate Overview:

    • A prototypical asthmatogen (types include toluene diisocyanate, methylene diisocyanate).

  • Common Uses:

    • Found in two-component systems for foams, spray paints, and insulations.
    • Approximately 50-100,000 workers exposed; around 5% develop asthmatic reactions.

  • Sensitization Process:

    • Initial sensitization may take years; often follows an incident like infection or larger exposure events.
    • Symptoms may be immediate or delayed; nocturnal wheezing possible.

  • Treatment Considerations:

    • Employment decisions may hinge on managing sensitized asthma.
    • Many develop lower thresholds for asthma attacks over time.

Challenges in Diagnosis and Management

  • Clinical Testing:
    • Importance of peak flow measurements to monitor lung function over time.
    • Decrements in FEV1 indicative of occupational asthma response.
  • Graphical Analysis:
    • Results from methacholine challenge tests reveal response dynamics distinct from non-sensitized individuals.