Abstract
Tourette syndrome is a chronic tic disorder characterized by motor and vocal tics. Comorbidities such as attention deficit hyperactivity disorder and obsessive compulsive disorder can be found. The overlap between neuroanatomical regions and neurotransmitter systems in the olfactory system and the pathophysiology of Tourette syndrome let us hypothesize altered olfactory performance in Tourette syndrome. The main objective of this study was to systematically assess olfactory functioning in subjects with Tourette syndrome and to compare it to healthy controls. We assessed 28 adults with Tourette syndrome (age 33.1±9.4 years, disease duration 23.7±9.7 years) and 28 healthy controls (age 32.9±9.0 years) matched in regard to age, sex, education and smoking habits. The “Sniffin Sticks” test battery was applied to assess odor threshold, discrimination, and identification. Additionally, the combined score of the odor threshold test, the odor discrimination test and the odor identification test of the “Sniffin Sticks” test battery was calculated. Although it was not the primary aim of this study, we assessed whether tics and comorbidity could contribute to olfactory alterations in adults with Tourette syndrome. Therefore, clinical scores were used to assess severity of tics and co-morbidity such as attention deficit hyperactivity disorder, obsessive compulsive disorder, anxiety and depression in subjects with Tourette syndrome. Pathology of the nasal cavities was excluded with rhinoendoscopy. Independent sample t-tests were applied to compare performance in olfactory tests. In the case of statistically significant differences (critical p-value: 0.05), multiple linear regression analysis was carried out to explore whether tic severity, social impairment, co-morbidity or medical treatment had an impact on the differences found. Descriptive values are reported as mean ± standard deviation. Tourette syndrome subjects showed lower combined scores (Tourette syndrome subjects 31.9 ± 5.1 versus healthy controls 35.0 ± 3.1; p = 0.007), odor identification scores (Tourette syndrome subjects 12.4 ± 2.0 versus healthy controls 13.7 ± 1.4; p = 0.008) and odor discrimination scores (Tourette syndrome subjects 12.1 ± 2.1 versus healthy controls 13.2 ± 1.6; p = 0.041) in comparison to healthy subjects, while there was no difference in odor threshold (Tourette syndrome subjects 7.3 ± 2.7 versus healthy controls 8.1 ± 2.2; p = 0.22). Seven out of 28 Tourette syndrome subjects (25%) scored in the range of the age- and sex-dependent combined score for hyposmia, while two of 28 healthy controls (7%) had a similar low combined score. None of the participants were found to have functional anosmia. Multiple linear regression analyses suggest that social impairment may a predictor for low combined score and odor identification score in Tourette syndrome subjects (p = 0.003). Compared to healthy controls, altered olfaction in adults with Tourette syndrome was found in this study. Normal odor threshold level but lower scores at tasks involving supra-threshold odor concentrations point towards a central-nervous alteration in the processing of olfactory information in Tourette syndrome.
Highlights
Tourette Syndrome (TS) is a chronic tic disorder characterized by the presence of fluctuating motor and vocal tics [1,2,3]
Compared to healthy controls, altered olfaction in adults with Tourette syndrome was found in this study
Values are means ± standard deviations; YGTSS = Yale Global Tic Severity Scale; Obsessive compulsive symptoms (OCS) = obsessive compulsive symptoms as assessed by the OCS checklist; BSI = Brief Symptom Inventory to assess depression or anxiety; WURS—ADHD = attention deficit hyperactivity disorder as assessed by the German version of the Wender-UtahRating-Scale; TMT-A/-B = Trail Making Test–Part A/B; Digital Span test according to Demuth et al Ãp-values as assessed by independent samples t-test, two-tailed
Summary
Tourette Syndrome (TS) is a chronic tic disorder characterized by the presence of fluctuating motor and vocal tics [1,2,3]. TS typically occurs during childhood and puberty, but may persist into adulthood [2,3] Sensory abnormalities such as the premonitory urge phenomena, enhanced sensory perception, and alleviating maneuvers are reported in TS [1,4,5]. Normal odor threshold but altered subjective sensitivity to odors in adults with TS was reported [1]. The pattern suggestive for olfactory decline of central nervous origin is (almost) unaffected odor threshold but altered odor identification and discrimination [4,6,7]. To the best of our knowledge, a systematic assessment of olfactory functioning in subjects with TS, including an odor threshold test and tests for odor identification and odor discrimination, has not been reported before
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