title: Multiple chemical sensitivity: on the scent of central sensitization.
abstract: BACKGROUND
  Multiple Chemical Sensitivity (MCS) is a chronic condition characterized by recurrent, non-specific symptoms in response to chemically unrelated exposures in non-toxic concentrations. Although the pathophysiology of MCS remains unknown, central sensitization may be an important factor contributing to the clinical manifestations.
  
  
  OBJECTIVE
  To use quantitative sensory testing (QST) to study central hyperexcitability and multiple aspects of central sensory processing in MCS patients without comorbid overlapping disorders and to compare the results with those among matched controls.
  
  
  METHODS
  15 MCS patients and 15 healthy matched controls underwent QST to assess the following aspects of pain: capsaicin-induced secondary punctate hyperalgesia, stimulus response function (SRF) to punctate mechanical stimuli before and after capsaicin injection, temporal summation to punctate stimuli post capsaicin injection, pressure pain thresholds, heat pain thresholds, tonic heat stimulation and conditioning pain modulation (CPM: formerly known as diffuse noxious inhibitory control or DNIC).
  
  
  RESULTS
  The mean area of capsaicin-induced secondary punctate hyperalgesia was significantly larger in MCS patients than in controls at 5, 30 and 60 min post capsaicin injection (p=0.01). In addition MCS patients reported higher ratings in response to punctate mechanical stimuli assessed by SRF compared with controls (p<0.001). The CPM test induced significantly higher pain ratings in patients than in controls (p=0.002). We found no group differences in pressure pain and heat pain thresholds, temporal summation to punctate stimuli post capsaicin injection, capsaicin and tonic heat pain ratings or CPM effect.
  
  
  CONCLUSIONS
  Increased capsaicin-induced secondary punctate hyperalgesia was demonstrated in MCS patients without comorbid, overlapping disorders, suggesting facilitated central sensitization in MCS.
authors.affiliation: The Danish Research Centre for Chemical Sensitivities, Department of Dermato-Allergology, Copenhagen University Hospital Gentofte, Denmark. mathtr01@geh.regionh.dk
authors.forename: Marie Thi Dao
authors.initials: MT
authors.lastname: Tran
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Ron
authors.initials: R
authors.lastname: Kupers
authors.forename: Jesper
authors.initials: J
authors.lastname: Elberling
mesh_terms: D000328:Adult; D002211:Capsaicin / Q000008:administration & dosage; D059333:Central Nervous System Sensitization; D003080:Cold Temperature; D005260:Female; D006358:Hot Temperature; D006801:Humans; D006930:Hyperalgesia / Q000150:complications* / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D018777:Multiple Chemical Sensitivity / Q000150:complications* / Q000503:physiopathology; D010147:Pain Measurement; D011795:Surveys and Questionnaires
chemical_list: D002211:Capsaicin