D2.146 - Occupational Asthma due to Subtilisin: the power of specific inhalation challenge
Case report
Purpose: to confirm the potential of subtilisin, a high-molecular-weight (HMW) proteolytic enzyme, to induce asthma and reinforce the evidence that the specific inhalation challenge (SIC) remains the gold standard test for the diagnosis of occupational asthma (OA). Written informed consent was obtained from the patient for the publication of this case.
Case Report: A 51-year-old nurse, responsible for the sterilization of surgical instruments using a liquid disinfectant containing subtilisin, developed respiratory symptoms three months after starting this task. After a positive bronchial provocation challenge with methacholine (PD20: 91.99 µg), the patient was diagnosed with bronchial asthma. Skin prick tests with allergens from the sanitary series, as well as both diluted (1:10) and pure enzymatic sterilizing solution used at work, were negative.
In the clinical suspect of OA induced by subtilisin, the patient thus underwent a SIC at the Occupational Medicine Unit of Padua University Hospital.
On the first day, baseline global spirometry, fractional exhaled nitric oxide (FeNO), Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO), blood and skin prick tests were all negative.
On the second day (control day), the patient was exposed to an inert substance (water vapor) for one hour, and FEV1 values remained stable throughout the 7-hour monitoring period, with no variation exceeding 10%.
On the third day, the patient inhaled the diluted enzymatic sterilizing solution (25mL/4L; concentration 0.625%). After 3 minutes of exposure, FEV1 decreased by 30% from the baseline value (1.57 L vs 2.26 L). After the 7-hours monitoring, FeNO concentration was elevated (45 ppb).
This case report, the first in Italy to confirm OA due to subtilisin through SIC, shows that a negative result from skin prick tests is insufficient to exclude occupational asthma induced by HMW agents. Our patient exhibited an immediate response at the third minute of SIC and an increase in FeNO levels after the specific bronchoprovocation test.
