PLoS ONE (Aug 2009)

Pain reactivity and plasma beta-endorphin in children and adolescents with autistic disorder.

  • Sylvie Tordjman,
  • George M Anderson,
  • Michel Botbol,
  • Sylvie Brailly-Tabard,
  • Fernando Perez-Diaz,
  • Rozenn Graignic,
  • Michèle Carlier,
  • Gérard Schmit,
  • Anne-Catherine Rolland,
  • Olivier Bonnot,
  • Séverine Trabado,
  • Pierre Roubertoux,
  • Guillaume Bronsard

DOI
https://doi.org/10.1371/journal.pone.0005289
Journal volume & issue
Vol. 4, no. 8
p. e5289

Abstract

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BACKGROUND: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 beta-endorphin levels and their relationship in a large group of individuals with autism. METHODOLOGY/PRINCIPAL FINDINGS:The 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 beta-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 (Delta 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 beta-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/SIGNIFICANCE:The greater heart rate response to venepuncture and the elevated plasma beta-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.