Thermal Pain Perception in Adults with Asperger Syndrome

Background:  

Case studies and caregiver reports often describe pain hypo- or insensitivity in individuals with autism spectrum disorders. Diminished or altered observable reactions to pain might have several reasons, including true hyposensitivity but also communication deficits or altered emotional expression in body language or a different understanding of the concept of pain. Experimental studies that assessed pain perception in autism spectrum disorders are rare. To our knowledge, no study has measured pain thresholds in individuals with autism spectrum disorders empirically yet.

Objectives:  

The aim of our study was to assess objective pain measurements in the thermal domain (absolute temperature thresholds) in individuals with Asperger syndrome and typically developed control participants, and to relate these measures to their subjective pain experience in terms of intensity and quality ratings and verbal attributes at the measured heat levels as well as to autistic personality traits.

Methods:  

Thermal pain onset (TPO - the temperature at which heat perception turns into pain) and thermal pain tolerance (TPT - the temperature at which pain perception is not tolerated any longer) were measured at the volar forearm in 29 adults with Asperger syndrome (AS) and 29 control participants (CG). To prevent injuries, thermal stimulation stopped automatically at a temperature of 52°C. Thermal pain range was calculated as the difference of the mean TPT and TPO. Subjective pain experience was rated at TPO and TPT regarding quality (from neutral to uncomfortable) and intensity (from no pain to maximal self experienced pain) and additionally assessed with the McGill Pain Questionnaire. Autistic personality traits were assessed with Baron-Cohen’s Autism Questionnaire (AQ), Alexithymia was assessed with the Toronto Alexithymia Scale. Performance and verbal IQ were estimated with two tests of the Wechsler Adult Intelligence Scale (WAIS-III). 

Results:  

Thermal pain range was higher in the AS group. Absolute temperature levels of thermal pain onset and thermal pain tolerance did not differ significantly between the two groups. Neither differed the subjective pain intensity and pain quality ratings of the two groups. However, within the AS group, individuals with more pronounced autistic traits (in terms of higher AQ scores) tolerated significantly higher temperatures and rated their subjective pain experience as lower regarding pain intensity and pain quality. The same was observed in AS individuals with higher alexithymia scores, which themselves were highly correlated with the AQ scores. AS individuals with higher AQ scores chose less words on the McGill Pain Questionnaire to describe their pain experience. Over all participants, those with higher IQ estimates showed lower pain quality ratings at pain onset (TPO).

Conclusions:  

Our results could be interpreted as signs of an altered understanding of the concept of pain in individuals with Asperger syndrome especially those more severely affected. The absolute temperature thresholds of thermal pain onset and tolerance did not differ from the not affected control group, indicating intact thermal pain sensitivity.