Sensory sensitivity to external stimuli in Tourette syndrome patients

Abstract

Patients with Tourette Syndrome often state that their sensitivity to sensations is equally or more disruptive than are motor tics. However, their sensory sensitivity is not addressed by standard clinical assessments nor is it a focus of research. This lapse likely results from our limited awareness and understanding of the symptom. In this study (1) we defined the patients' experience of sensitivity to external stimuli in detail, and (2) we tested 2 hypotheses regarding its origin. First, we interviewed in depth and administered a lengthy questionnaire to adult Tourette patients (n = 19) and age-matched healthy volunteers (n = 19). Eighty percent of patients described heightened sensitivity to external stimuli, with examples among all 5 sensory modalities. Bothersome stimuli were characterized as faint, repetitive or constant, and nonsalient, whereas intense stimuli were well tolerated. We then determined whether the sensitivity could be the result of an increased ability to detect faint stimuli. After measuring the threshold of detection for olfactory and tactile stimuli among the patients and healthy volunteers, we found no significant differences between them for either sensory modality. These results indicate that patients' perceived sensitivity derives from altered central processing rather than enhanced peripheral detection. Last, we assessed one aspect of processing: the perception of intensity. When subjects rated the intensity of near-threshold tactile and olfactory stimuli, there was a surprising difference: Tourette patients more frequently used the lowest range of the scale than did healthy volunteers. Future research is necessary to define the anatomical and physiological basis of the patients' experience of heightened sensitivity. © 2011 Movement Disorder Society.

Figure 1. Subjective report of sensitivity to external stimuli

A. Responses to single questions asking if the subject had a heightened sensitivity to external stimuli in general, or sensitivity to specific sensory modalities. Statistically significant differences (p<0.01) between TS patients and HVs are indicated by an asterisk. B. Responses to questions describing specific scenarios involving tactile stimuli. This pattern of enhanced sensitivity to faint stimuli but not to intense stimuli among TS patients was similar for all sensory modalities.

Figure 2. Thresholds of detection for olfactory and tactile stimuli

Tactile stimuli were presented both to the lower leg, and to the site of an active tic in each TS patient, matched 1:1 in HVs. Stimulus strength number corresponds to its order within the geometric series: a higher value represents a weaker stimulus. There was no significant difference between the thresholds for TS patients and HVs (p>0.01) Error bars indicate SD.

Figure 3. Subjective intensity ratings of near-threshold stimuli

A. The average scores for stimuli one level above threshold (T+1) and four levels above threshold (T+4) are shown. There was no significant difference between TS and HV groups (p>0.01). Error bars indicate SD. B. The distribution of high scores in each group is plotted for tactile stimuli at the tic site. Quartiles of the intensity scale are: 1=0–25, 2=26–50, 3=51–75, 4=76–100. Note that, in contrast to HVs’ scores, the TS patients’ scores were significantly skewed toward the low end of the scale (p<0.0001).