OLFACTORY FUNCTION IN PATIENTS WITH HYPOGONADOTROPIC HYPOGONADISM - AN ALL-OR-NONE PHENOMENON

Hypogonadotropic hypogonadism (HH) refers to an endocrine defect of hy pothalamic origin resulting in gonadal hypoplasia and frequently assoc iated with anosmia or severely impaired olfactory function (Kallmann's syndrome). This apparently results from a disruption in the migration of neurons from the olfactory placode to the bulb and hypothalamus ea rly in development, and so provides a unique opportunity to investigat e olfactory function in human subjects with congenitally incomplete pe ripheral systems. Olfactory performance in 37 HH patients and 37 age-m atched controls was compared using a modified version of the Munich Ol faction Test. This test is based on the sniff-bottle method and includ es tests of (i) odor quality discrimination, (ii) intensity discrimina tion, (iii) detection thresholds, and (iv) recognition, hedonic evalua tion and identification ability. The patients could be divided into tw o distinct groups differing significantly on all four subtests and sho wing no overlap in performance: 20 anosmics, conforming to Kallmann's syndrome, and 17 apparent normosmics whose performance was slightly po orer, but not significantly different to that of the controls. The une xpected failure to find a continuum of olfactory dysfunction now raise s the question whether HH with or without anosmia represents two syndr omes with distinct etiologies, or rather reflects the ability of the o lfactory system to function well despite morphological impairment.