An objective olfactory evaluation and its correlation with magnetic resonance imaging findings in Asian Indian patients with idiopathic hypogonadotropic hypogonadism.

OBJECTIVE

Idiopathic hypogonadotropic hypogonadism (IHH) can be associated with subnormal sense of smell. The objective of our study was to determine if there is a correlation between the olfactory phenotype (clinical smell test) of IHH patients and structural abnormalities in the olfactory apparatus on magnetic resonance imaging (MRI).

METHODS

This was a single-center prospective case control study. Forty-one IHH patients underwent a brief University of Pennsylvania Smell Identification Test (UPSIT) and an MRI of the olfactory apparatus. The size of the olfactory sulcus and bulb were quantified and compared with the normative data of 40 controls. Agreement between UPSIT and MRI results was assessed using the kappa index.

RESULTS

MRI showed that the olfactory apparatus was normal in 17 patients, hypoplastic in 14, and aplastic in 10. All 13 patients who complained of anosmia and 12 of 28 patients who reported normosmia had a low UPSIT score. Thus, 25 patients had Kallmann syndrome (KS) and 16 were normosmic IHH (nIHH). MRI revealed abnormalities in 68% of KS and 37.5% of nIHH patients. The MRI abnormalities in KS patients were aplasia (56%) and hypoplasia (44%). All 6 nIHH patients with abnormal MRI had hypoplasia. A significant positive correlation (r = 0.61; P<.01) between olfactory bulb volume (from MRI) and smell-test score was found, and there was good agreement (kappa index, 0.72) between anosmia and the presence of an aplastic olfactory apparatus.

CONCLUSION

Self-reporting of the sense of smell significantly underestimates olfactory phenotype; hence, we recommend an objective smell test to distinguish KS from nIHH. Olfactory phenotype correlates well with MRI quantification of the olfactory apparatus in IHH.