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Occupational Asthma . Tee L. Guidotti The George Washington University. Presentation of Occ Asthma. Immediate hypersensitivity reaction Immediate bronchospasm Isolated late response (usually sensitizer-induced) Sleep disorder Variable/dual response . Types of Occupational Asthma.

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Occupational Asthma

Tee L. Guidotti

The George Washington University


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Presentation of Occ Asthma

  • Immediate hypersensitivity reaction

  • Immediate bronchospasm

  • Isolated late response (usually sensitizer-induced)

  • Sleep disorder

  • Variable/dual response


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Types of Occupational Asthma

  • New Onset

    - Sensitizer-induced

    - Irritant induced

  • Aggravation of underlying asthma

  • Reactive airways dysfunction syndrome (RADS)

  • Cold air- or exercise-induced syndrome

  • Airways reactivity secondary to hypersensitivity pneumonitis


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Sensitizer-induced

Specific antigen

Minimal exposure

Stereotyped response

PPE often insufficient to control symptoms

Medical removal usually necessary

Irritant-induced

Any irritant

Moderate to heavy exposure

Often variable

PPE often effective in preventing episodes

Medical removal the last resort

Occupational Asthma


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Sensitizer-Induced Occ Asthma

  • Sensitization to a specific antigen

    - low molecular-weight, “hapten”

    - high molecular weight

  • Reaginic Ab, mostly IgE, mediated

  • Presentation variable

    - late phase reactivity

    - immediate sensitivity

    - dual or variable responsiveness


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Sensitizer-Induced Asthma 2

  • Sensitization may occur at <OEL

  • Sensitizers may also be irritants (e.g. TDI,TMA)

  • Prior history of atopy does not predict risk of asthma!

  • Therefore no basis of exclusion of persons with allergies from workplace


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Low MW

Isocyanates

Anhydrides

Metal salts

Epoxy resins

Fluxes

Persulfate

Aldehydes

High MW

Pharmaceuticals

Animal proteins

Latex

Cereals

Seafood

Proteolytic enzymes

Wood constituents

Common Sensitizers(Incomplete List!)


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Irritant-Induced Occupational Asthma

  • More common, clinically, than sensitizer-induced

  • Often represents clinical expression of airways hyperactivity + irritant exposure

  • May be induced by any irritating exposure

  • Usually history of intolerance to second-hand tobacco smoke

  • Some irritant exposures may also be sensitizing: CHO, TDI,TMA

  • Classic example is “hot wire” asthma


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RADS

  • Acute onset following exposure to irritant

  • Generally exposure of moderate severity

  • Prognosis good but may have several years of airway hyperactivity and sequelae

  • Often associated with:

    • upper airway problems

    • sleep disorder

  • Independent of prior history of airways reactivity

  • Conventional management


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Aggravational Asthma

  • Very common

  • Existing airways reactivity:

    • asthma

    • hay fever and rhinitis

    • other airways disease (e.g. COPD)

  • Initial condition not occupational

  • Moderate irritant exposure

  • Provokes airways response

  • Usually self-limited



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Immediate response

  • Same shift, rapid onset

  • Reaginic antibody if sensitizer-induced

  • Acute mediators

  • Responds to conventional asthma Rx

  • Often difficult to distinguish from conventional asthma

  • Irritant-induced tends to be milder


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Late Responders

  • Onset of bronchospasm hours after exposure

  • Usually wheezing post-shift

  • Often presents as a sleep disorder

  • If isolated, usually associated with certain antigens (Western red cedar, TDI)

  • Often combined


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Dual/Variable effects

  • Dual responders may combine immediate + late responses

  • Variations may include cyclic bronchospasm (esp. Western red cedar)

  • May be prolonged, sustained response (TDI, byssinosis)

  • Usually slow recovery, relatively refractory to conventional Rx


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Special Cases

The following subsets of occupational asthma have special features:

  • Laboratory animal sensitivity (high risk of anaphylaxis)

  • Cotton dust, byssinosis

  • Grain dust

  • Hypersensitivity pneumonitis may have an airways component


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Cold Air / Exercise-Induced Asthma

  • May be associated with:

    • dry cold air

    • exertion

    • hyperventilation

  • Work in cold, dry climates

  • Immediate response, short duration

  • Further exercise may improve airflow!

  • Mechanism: airway drying and cooling

    • stimulates vagal receptors

    • histamine, mediator release from mast cells


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Principles of Evaluation

  • Demonstrate airways reactivity

    - History

    - Presence of wheezing

  • Spirometry

  • Methacholine challenge

  • Bronchoprovocation or substitute

    - Symptom diary

    - Pre/post shift


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Methacholine Challenge

  • + Test confirms airways reactivity only

  • A functional test not specific for asthma

    - atopy

    - transient reactivity

  • Bronchoprovocation with with specific antigen preferable to diagnose sensitizer-induced asthma

  • -Tests can occur with quiescent occ asthma


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Risks of Bronchoprovocation

  • Anaphylaxis

  • Iatrogenic reaction

  • Sensitization


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Ancillary Tests

  • Clinical immunology

    - skin prick tests

    - RAST

    - ELISA

  • PEF or FEV1, symptom and medication diary

  • Pre/post shift and/or holiday PFTs

  • Work place HHE


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Management

  • Conventional Rx for asthma

  • Medical removal – consider options

  • Physician’s First Report

  • Impairment Assessment (c.f. AMA guidelines)

  • Avoid irritants

  • Evaluate PPE


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Compensation Management

  • Document causation

  • Document impairment (episodic?)

  • Medical removal required?

  • Claimant factors

    - degree of impairment

    - age

    - retraining

    Impairment – Disability


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Pop Health Management

  • Treat as “Sentinel event”

  • Surveillance

  • Identification of specific hazard when possible

  • Hazard Control

    - engineering controls

    - PPE


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