Olfactory Dysfunction in Nmo Vs MS

Background: Whilst optic nerves and spinal cord are preferentially affected in NMO, it is widely recognised that NMO pathology is not restricted to these areas. Emerging evidence suggests that olfactory dysfunction may be a feature of NMO. In this study, we provide independent confirmation that olfactory dysfunction not only occurs in NMO, but is more frequent and severe than in MS.  Additionally, we provide evidence, for the first time, that olfactory deficits correlate significantly with measures of disability in NMO. 

Objectives: To evaluate the presence and extent of olfactory dysfunction in AQP-4 positive neuromyelitis optica (NMO) compared to multiple sclerosis (MS) and to relate these findings to clinical factors, including measures of disability.

Methods: A prospective study at a tertiary NMO and MS Centre evaluating olfactory function using the Sniffin’ Sticks Identification Test in a cohort of clinically definite NMO (n=19) and MS (n=27) patients in whom demographic and clinical measures of disability (European Database for Multiple Sclerosis (EDMUS)) were available.

Results: NMO patients were slightly older and had a shorter duration of disease compared to the MS group with no significant differences in disability being observed between groups.  Olfactory dysfunction was not only more frequent in NMO compared to MS (NMO – 10/19 (52.6%) versus MS – 6/27 (22.2%), p <0.05) but also more severe when adjusted for age, sex, and duration of disease.  No patients from either disease group reported subjective olfactory disturbance. Olfactory dysfunction in NMO and MS correlated significantly with age (r = -0.454, p = 0.002) and EDMUS score (r= -0.381, p = 0.009), with these relationships being driven mostly by the NMO group.

Conclusions: Olfactory dysfunction occurs frequently in NMO , is more severe than the olfactory loss seen in MS, and correlates with measures of clinical disability.   These findings expand the widening clinical spectrum of NMO.