Abstract
BackgroundReports of reduced pain sensitivity in autism have prompted opioid theories of autism and have practical care ramifications. Our objective was to examine behavioral and physiological pain responses, plasma β-endorphin levels and their relationship in a large group of individuals with autism.Methodology/Principal FindingsThe study was conducted on 73 children and adolescents with autism and 115 normal individuals matched for age, sex and pubertal stage. Behavioral pain reactivity of individuals with autism was assessed in three observational situations (parents at home, two caregivers at day-care, a nurse and child psychiatrist during blood drawing), and compared to controls during venepuncture. Plasma β-endorphin concentrations were measured by radioimmunoassay. A high proportion of individuals with autism displayed absent or reduced behavioral pain reactivity at home (68.6%), at day-care (34.2%) and during venepuncture (55.6%). Despite their high rate of absent behavioral pain reactivity during venepuncture (41.3 vs. 8.7% of controls, P<0.0001), individuals with autism displayed a significantly increased heart rate in response to venepuncture (P<0.05). Moreover, this response (Δ heart rate) was significantly greater than for controls (mean±SEM; 6.4±2.5 vs. 1.3±0.8 beats/min, P<0.05). Plasma β-endorphin levels were higher in the autistic group (P<0.001) and were positively associated with autism severity (P<0.001) and heart rate before or after venepuncture (P<0.05), but not with behavioral pain reactivity.Conclusions/SignificanceThe greater heart rate response to venepuncture and the elevated plasma β-endorphin found in individuals with autism reflect enhanced physiological and biological stress responses that are dissociated from observable emotional and behavioral reactions. The results suggest strongly that prior reports of reduced pain sensitivity in autism are related to a different mode of pain expression rather than to an insensitivity or endogenous analgesia, and do not support opioid theories of autism. Clinical care practice and hypotheses regarding underlying mechanisms need to assume that children with autism are sensitive to pain.
Highlights
It has often been stated that individuals with autistic disorder have reduced pain sensitivity
The results suggest strongly that prior reports of reduced pain sensitivity in autism are related to a different mode of pain expression rather than to an insensitivity or endogenous analgesia, and do not support opioid theories of autism
Decreased compared to normals Similar to normals Decreased compared to normals or schizophrenics Increased compared to normals Similar to normals Decreased compared to normals or girls with Rett’s Increased compared to normals or girls with Rett’s Increased compared to normativecontrol values Increased compared to normals Increased compared to normals or PDD Increased compared to normals Increased in selfinjurious behaviors (SIB) and low pain sensitivity Increased compared to normals Decreased compared to normal adults Similar to normals
Summary
It has often been stated that individuals with autistic disorder have reduced pain sensitivity. The opioid theories in autism have been based on 1) symptom profiles seen in autism, 2) reported therapeutic effects of opiate antagonists and 3) reported abnormalities in opioid levels measured in individuals with autistic disorder, such as b-endorphin (BE). There are apparent symptom similarities between autism and opiate addiction or behavioral states following administration of opiate and opioid agents in animals [13,14,15,16,17,18,19]. Autistic children and opiate-addicted organisms both appear less sensitive to pain, less emotional and asocial. Reports of reduced pain sensitivity in autism have prompted opioid theories of autism and have practical care ramifications. Our objective was to examine behavioral and physiological pain responses, plasma b-endorphin levels and their relationship in a large group of individuals with autism
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