Work-Related Asthma Prognosis After Specific Inhalation Challenge

Key Takeaways

• Among questionnaire respondents assessed for work-related asthma using SIC, 79% reported no current exposure to the suspected causal agent.
• Difficult-to-treat asthma was more common than medication-free clinical remission at long-term follow-up.
• Neither asthma outcome differed significantly between positive- and negative-SIC groups.
• Occupation changes were significantly more frequent after a positive SIC than after a negative result.
• Difficult-to-treat asthma at diagnosis was associated with difficult-to-treat asthma years later.

For people assessed for possible work-related asthma, how do symptoms and medication needs evolve years after diagnostic testing? A positive specific inhalation challenge (SIC) established occupational asthma in this cohort, but whether challenge status tracks with subsequent asthma is a separate question. Patients reported their longer-term symptoms and treatment needs through follow-up questionnaires.

Investigators assessed long-term work-related asthma outcomes by sending questionnaires to 618 people with work-related asthma; 44% responded a median of 8.5 years after SIC. This was observational follow-up, with no treatment assigned.

A positive SIC established occupational asthma, and respondents with positive and negative challenge results formed the comparison groups. Difficult-to-treat asthma meant poor symptom control, at least two asthma exacerbations, or at least one serious exacerbation over the preceding year despite Global Initiative for Asthma (GINA) steps 4–5 medication. Off-treatment clinical remission required no asthma symptoms, exacerbations, or medication during the preceding year.

At follow-up, 32% of respondents had difficult-to-treat asthma, while 4% met the definition of off-treatment clinical remission; neither outcome differed significantly by SIC result. Older age, a low Asthma Control Test (ACT) score, GINA steps 4–5 medication, and difficult-to-treat asthma at diagnosis were associated with difficult-to-treat asthma at follow-up. The diagnosis-time difficult-to-treat classification had the largest reported association, with an adjusted odds ratio (OR) of 5.73.

Occupation changes were reported more frequently after a positive SIC than after a negative result (67% versus 47%; P = .002). The questionnaire findings do not establish whether changing occupations altered subsequent symptoms or medication requirements.

Only a minority of those contacted returned questionnaires, so respondents may not represent everyone invited to participate. Follow-up information was questionnaire-reported, and neither the SIC-group comparison nor the occupational observations establish causal effects. A nonsignificant difference in asthma outcomes does not establish equivalent prognoses for positive- and negative-challenge groups.

The authors concluded that medication-free clinical remission was rare and long-term asthma outcomes were largely comparable across SIC groups. They also identified worse asthma status at diagnosis as associated with difficult-to-treat asthma at follow-up.

Clinician Questions

Did employment after specific inhalation challenge apply to all respondents with work-related asthma?

No. Employment was reported for the working-age subgroup, not for all respondents; most people in that subgroup reported being employed.

How many respondents with work-related asthma had positive versus negative specific inhalation challenges?

Among the 274 respondents who completed long-term follow-up after SIC, 110 had a positive result and 164 had a negative result. A positive result established occupational asthma in this cohort; negative-result respondents remained the work-related asthma comparison group.