title: Reduced response to the thermal grill illusion in chronic pain patients.
abstract: OBJECTIVE
  Sensory illusions may reveal fundamental features of the nervous system. The thermal grill illusion is such a pain illusion, where interlaced warm and cool temperature bars (thermal grill) produce a paradoxical burning sensation. Previous studies have only systematically investigated the thermal grill illusion in pain-free volunteers. The objective of this study was to investigate whether the response to the thermal grill illusion was tolerable in patients with chronic pain and whether the response differed between patients with chronic pain and pain-free volunteers.
  
  
  METHODS
  Sixteen pain-free participants and 18 chronic pain patients (seven not receiving opioids and 11 receiving opioids).
  
  
  METHODS
  The thermal grill response was investigated using a custom-built thermal grill. Heat and cold pain thresholds were also determined.
  
  
  RESULTS
  Chronic pain patients reported less intense pain, heat, and unpleasantness to the thermal grill compared with pain-free participants; in particular, there was an overall main effect for significantly less heat from the thermal grill compared with pain-free participants (P = 0.016). At the 22/38°C combination, although the majority of pain-free participants experienced the illusion to some degree, the majority of pain patients in both groups did not (median pain score 0). Although perceived heat from the thermal grill was significantly lower in chronic pain patients, both heat and cold pain thresholds did not differ among the three populations.
  
  
  CONCLUSIONS
  This preliminary data suggest that the thermal grill response may provide insights into pain sensitivity that are not detected by conventional thermal quantitative sensory testing.
authors: Discipline of Pharmacology, School of Medical Sciences, University of Adelaide, Adelaide, South Australia, Australia.
authors: Nicole M
authors: NM
authors: Sumracki
authors: Femke T A
authors: FT
authors: Buisman-Pijlman
authors: Mark R
authors: MR
authors: Hutchinson
authors: Melanie
authors: M
authors: Gentgall
authors: Paul
authors: P
authors: Rolan
mesh_terms: D000328:Adult; D000368:Aged; D000701:Analgesics, Opioid / Q000627:therapeutic use; D016022:Case-Control Studies; D059350:Chronic Pain / Q000188:drug therapy / Q000503:physiopathology*; D003080:Cold Temperature; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D020886:Somatosensory Disorders / Q000503:physiopathology*; D013697:Thermosensing / Q000502:physiology*
chemical_list: D000701:Analgesics, Opioid
keywords: Chronic Pain; Cold Pain Thresholds; Heat Pain Thresholds; Pain Model; Thermal Grill Illusion