House dust mite hypersensitivity: morning dipping and severity of wheeze.

Atopic subjects with asthma are frequently hypersensitive to house dust mite (Dermatophagiodes pyteronyssinus). Exaggerated nocturnal or early morning wheezing might occur in these patients, because of exposure to the allergen during the night, particularly in view of the biphasic response that it produces in airway resistance. This might be of diagnostic value in determining the relevance of house dust mite to the asthma of a particular subject. This hypothesis was tested in 100 patients with diurnal variation in airway obstruction, 78 of whom were predominantly asthmatic. Hypersensitivity to house dust mite was measured by a simple prick test. Morning dipping was seen in patients without hypersensitivity to house dust mite. There was no significant quantitative relationship between morning dip and hypersensitivity. There was a significant relationship between morning dip and severity of wheeze. This study confirms the view that morning dipping is a reflection of the severity of asthma, rather than a feature of any particular type.