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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Occupational Asthma

• 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

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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 ltOEL
• 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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Common Sensitizers(Incomplete List!)

• Low MW
• Isocyanates
• Anhydrides
• Metal salts
• Epoxy resins
• Fluxes
• Persulfate
• Aldehydes

• High MW
• Pharmaceuticals
• Animal proteins
• Latex
• Cereals
• Seafood
• Proteolytic enzymes
• Wood constituents

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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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Patterns of Airways Response
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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
• Physicians 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