Initiation of smell function in patients with congenital hyposmia.

Background: Patients 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.

Methods: Smell 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, 200-800mg daily for periods of 2-36months with evaluation of smell function and serum theophylline measured at intervals of 2-6months.

Results: In 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 200-800mg of oral theophylline for periods of 2-19months.

Interpretation: This 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.