Olfactory Function In Patients With Multiple Sclerosis

ObjectiveMultiple sclerosis(MS)is an autoimmune demyelinating disease of the central nervous system.MS is the most common cause of neurological disorders in young adults.Subcortical,periventricular,infratentorial structures and spinal cord are the most common sites involved.According to the different parts of the central nervous system involved,MS patients exhibit different symptoms,especially the optic nerve and spinal cord symptoms.Atypical symptoms include fatigue,mental symptoms,slurred speech and difficulty swallowing.Olfactory dysfunction has been reported in many neurodegenerative diseases,while olfactory function of MS has been few studied.In this survey,we explored the olfactory function in patients with MS,and the correlation factors to provide new evidence for the diagnosis and treatment of MS.MethodsJapanese T&T olfactometer threshold test was used to evaluate olfactory detection threshold(DT)and identification threshold(IT)in 30 MS patients and 30 age-and sex-matched healthy controls.Demographic,clinical information and subjective sense of smell were collected,Expanded Disability Status Scale(EDSS)were used to assess neurological function in patients.Mini-Mental State table(MMSE)and the Beck Depression self-assessment questionnaire(BDI)were used to assess cognitive and mental state of all subjects.MRI parameters such as olfactory bulb and olfactory-related gray matter volume changes were assessed.Correlation between clinical data and the olfactory function were analyzed by t-test and Pearson correlation statistic methodsResults1.There were 50%(15/30)MS patients proved abnormal IT scores;and 33.3%(10/30)MS patients presented with abnormal DT values.While,totally 30%(6/15)patients,both their IT and DT values over the normal range,but only one had subjective hyposmia.40%(6/15)of patients suffered with unilateral damage and 60%(9/15)of patients had bilateral damage,while no suffered anosmia2.The IT and DT were significantly higher in MS patients than healthy control(P=0.001,P=0.039).3.EDSS score was higher in MS patients group with identification dysfunction(MS-IT>1)than the normal group(MS-IT ≤1)(P=0.017).4.The IT score in MS patients with a disease duration more than 2 years was higher than the shorter duration group(P=0.003),however there was no significant difference of DT score between the two groups(P>0.05).5.There was no significant difference of BDI score between MS patients and healthy controls,MS patients with identification dysfunction and the normal group(P>0.05).6.EDSS score correlated with the IT values in MS patients(r=0.4399,P=0.0150).7.BDI score did not correlate with the IT or DT values in MS patients(r=0.2001,P=0.2891;r=-0.0209,P=0.9126).8.BDI score did not correlate with the IT or DT values in MS patients with olfactory dysfunction(r=0.0899,P=0.7499;r=-0.1308,P=0.6422).9.Patients had smaller OB volume than controls(P=0.012),and olfactory bulb volume correlate with the DT(r=-0.567,P=0.022).10.The significant grey matter volume reduction in MS was found in the parahippocampal gyri and olfactory cortex(FDR correction,P<0.05,cluster size>200voxels).Conclusions1.Patients with MS can experience decreased olfactory function,including the ability to detect odours and the ability to identifiy odours.2.Identification threshold was significantly impaired in patients with disease duration more than 2 years and in patients with a higher EDSS score.3.The BDI did not correlate with neither the IT nor DT in MS patients.There was no significant difference of BDI scores comparing between MS patients and healthy controls,MS-IT>1 group and MS-IT≤1 group.Thus olfactory dysfunction in MS patients could be independent of the depressive symptoms,however,the disease process might undermine the olfactory conduction system.4.Reduced OB and olfactory-related cortex volume may be responsible for MS patients.