Olfactory Function Assessment in Neuromyelitis Optica and Comparison with Multiple Sclerosis

Olfactory dysfunction may be an occasional presymptomatic sign of demyelinating diseases such as multiple sclerosis (MS), and neuromyelitis optica spectrum disease (NMOSD). In our study, we aim to investigate and compare olfactory functions in NMOSD and MS patients using a validated olfactory test tool and to evaluate the association of olfaction with disease duration, severity, and according to the presence of antibodies. This study was comprised of 16 NMOSD patients (9 women (56.2%), 7 men (43.8{\%})), 26 MS patients (17 women (65.4%), 9 men (34.6%)); 35 healthy volunteers (25 women (71.4%), 10 men (28.6%)) were included in the study as control group. The Connecticut Chemosensory Clinical Research Center olfactory test, developed for assessing orthonasal olfaction, was used. The odour identification score, smell threshold, and mean olfactory combined scores of NMOSD patients were significantly lower than the healthy controls and MS patients. All odour scores in control group and MS group did not differ significantly (p > 0.05). There was no difference in olfaction scores of NMOSD population with regard to AQP4-IgG positivity/negativity status. Our study suggests that olfactory dysfunction might be a part of clinical spectrum of NMOSD, so physicians treating patients with central nervous system demyelinating diseases should be aware of the potential for olfactory deficit and should counsel their patients accordingly.