Initiation of smell function in patients with congenital hyposmia

BackgroundPatients with congenital smell loss (hyposmia) are born without a sense of smell. They comprise two types. Type I patients have genetic abnormalities manifested by brain, gonadal and other somatic abnormalities. Type II patients have neither a family history of smell loss nor any somatic abnormalities. No systematic attempts to initiate smell function in Type II patients have been reported.MethodsSmell function was measured in 19 Type II congenital smell loss patients by both subjective responses and by olfactometry using measurements of detection and recognition thresholds, magnitude estimation and hedonics in response to four odors (pyridine, nitrobenzene, thiophene and amyl acetate) before and after treatment with oral theophylline, 200–800 mg daily for periods of 2–36 months with evaluation of smell function and serum theophylline measured at intervals of 2–6 months.ResultsIn 12 of the 19 Type II patients (63%) smell function was initiated for the first time and was quantitated by both subjective responses and by olfactometry. Initiation of smell function occurred after treatment with 200–800 mg of oral theophylline for periods of 2–19 months.InterpretationThis is the first systematic demonstration of initiation of smell in patients who were born without smell function. Oral theophylline presumably acts to increase both olfactory receptor growth, development and perpetuation and brain plasticity which enables them to recognize olfactory signals with initiation of olfactory function.