Absence of Hyper-Responsiveness to Methacholine after Specific Bronchial Provocation Tests in a Worker With Hydroxyapatite-Induced Occupational Asthma

Hydroxyapatite is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. Many modern implants, such as hip replacements and dental implants, are coated with hydroxyapatite. We report a patient with occupational asthma due to hydroxyapatite, proven by a specific inhalation challenge, who experienced an early asthmatic reaction after exposure to hydroxyapatite, without increased airway responsiveness to methacholine despite an increased eosinophil count in the peripheral blood. A 38-year-old male dental implant worker visited our allergy department for the evaluation of occupational asthma. He had treated dental implant titanium surfaces with hydroxyapatite for 1.5 years. One year after starting his employment, he noticed symptoms of rhinorrhea, paroxysmal cough, and chest tightness. His symptoms were aggravated during and shortly after work and subsided several hours after work. When he stopped working for 2 months because of his chest symptoms, he became asymptomatic. After restarting his work, his symptoms reappeared and were aggravated. A methacholine bronchial challenge test had a negative response. The following day, a specific bronchial provocation test with wheat powder was negative. On the third day, a specific bronchial provocation test with hydroxyapatite powder produced an early asthmatic response. On the fourth day, a methacholine bronchial challenge test was negative. Further studies are needed to evaluate the exact pathogenetic mechanism of hydroxyapatite-induced occupational asthma.