Retro- and orthonasal olfactory function in relation to olfactory bulb volume in patients with hypogonadotrophic hypogonadism.

Introduction: Idiopathic hypogonadotrophic hypogonadism with an olfactory deficit is defined as Kallmann syndrome and is distinct from normosmic idiopathic hypogonadotrophic hypogonadism.

Objective: Because olfactory perception not only consists of orthonasally gained impressions but also involves retronasal olfactory function, in this study we decided to comprehensively evaluate both retronasal and orthonasal olfaction in patients with idiopathic hypogonadotrophic hypogonadism.

Methods: This case-control study included 31 controls and 45 idiopathic hypogonadotrophic hypogonadism patients. All participants whose olfactory and taste functions were evaluated with orthonasal olfaction (discrimination, identification and threshold), retronasal olfaction, taste function and olfactory bulb volume measurement. The patients were separated into three groups according to orthonasal olfaction: anosmic idiopathic hypogonadotrophic hypogonadism, hyposmic idiopathic hypogonadotrophic hypogonadism and normosmic idiopathic hypogonadotrophic hypogonadism.

Results: Discrimination, identification and threshold scores of patients with Kallmann syndrome were significantly lower than controls. Threshold scores of patients with normosmic idiopathic hypogonadotrophic hypogonadism. were significantly lower than those of controls, but discrimination and identification scores were not significantly different. Retronasal olfaction was reduced only in the anosmic idiopathic hypogonadotrophic hypogonadism group compared to controls. Identification of bitter, sweet, sour, and salty tastes was not significantly different when compared between the anosmic, hyposmic, and normosmic idiopathic hypogonadotrophic hypogonadism groups and controls. Olfactory bulb volume was lower bilaterally in all patient groups when compared with controls. The olfactory bulb volume of both sides was found to be significantly correlated with threshold, discrimination and identification scores in idiopathic hypogonadotrophic hypogonadism patients.

Conclusion: 1) There were no significant differences in gustatory function between controls and idiopathic hypogonadotrophic hypogonadism patients; 2) retronasal olfaction was reduced only in anosmic patients but not in orthonasally hyposmic participants, possibly indicating presence of effective compensatory mechanisms; 3) olfactory bulb volumes were highly correlated with olfaction scores in the hypogonadotrophic hypogonadism group. The current results indicate a continuum from anosmia to normosmia in idiopathic hypogonadotrophic hypogonadism patients.