Enhancement of trigeminal chemosensory function in congenital anosmia and its contribution to the perception of odors.

Introduction and Aim: The majority of odorants activate both olfactory and trigeminal systems, and both systems are thought to contribute to the perception of odors. It is well known that, as compared to controls, patients suffering from congenital anosmia exhibit enhanced trigeminal responses, suggesting that trigeminal chemosensory input constitutes a unique way for people suffering from congenital anosmia to perceive odorants. The aim of this study was to investigate the contribution of the trigeminal system to the perception of odorants in congenital anosmia. Materials and Methods: We retrospectively reviewed 25 cases of patients suffering from congenital anosmia. Chemosensory function was investigated using psychophysical testing as well as the recording of trigeminal chemosensory event-related brain potentials (CSERPs). A structural MRI was also performed to evaluate the morphology of olfactory pathways. Results were compared to those obtained from 19 patients suffering from acquired anosmia (15 post-traumatic and 4 post-infectious) and 18 healthy controls. Results: The magnitude of the P2 wave of trigeminal CSERPs was significantly enhanced in congenital anosmia vs. healthy controls, and its latency was delayed. We also found a significant correlation between the psychophysical assessment of olfactory function and the magnitude of trigeminal CSERPs. This correlation was absent in acquired anosmia and healthy controls. Conclusion: Our results indicate that the chemosensory function of the trigeminal system is enhanced in congenital anosmia, as compared to acquired anosmia and healthy controls