Increased capsaicin-induced secondary hyperalgesia in patients with multiple chemical sensitivity.
OBJECTIVE
the underlying cause of pathophysiological mechanisms triggering multiple chemical sensitivity (MCS) remains disputed.Recently, alterations in the central nervous system, for example,central sensitization, similar to various chronic pain disorders, have been suggested. Capsaicin is used in experimental pain models to provoke peripheral and central sensitization. In patients with symptoms elicited by odorous chemicals capsaicin-induced secondary hyperalgesia and temporal summation were assessed as markers for abnormal central nociceptive processing together with neurogenic inﬂammation (ﬂare).


METHODS
sixteen patients fulﬁlling Cullen criteria for MCS and 15 eczema patients with airway symptoms induced by odorous chemicals (EC) were compared with 29 age-matched healthy controls.Participants underwent 2 intradermal injection of capsaicin (3.3 mM and 33 mM). Measurements included pain intensity, ﬂare, pinprick hyperalgesia, temporal summation, and McGill Pain Questionnaire score.


RESULTS
no diﬀerence was found in the ﬂare area between the groups. The capsaicin-evoked pain intensity was higher in MCS patients compared with controls (P<0.01, 33 mM). The area of secondary hyperalgesia was larger in both the patient groups compared with controls (P<0.05) at both capsaicin concentrations. Temporal summation was increased in MCS patients compared with controls(P<0.01). Further, in patients with comorbidity of ﬁbromyalgia, pain and chronic fatigue, pain continued after end stimulation, and the stimulus response function was enhanced compared with patients without comorbidity, and signiﬁcant to controls (P<0.05).


CONCLUSIONS
this is the ﬁrst study to show facilitated pain processing in MCS and EC patients with the most abnormal responses in MCS.
Danish Research Centre for Chemical Sensitivities, Gentofte Hospital University of Copenhagen.
Helle
H
Holst
Lars
L
Arendt-Nielsen
Holger
H
Mosbech
Jesper
J
Elberling
D002211:Capsaicin; D004357:Drug Synergism; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000150:complications / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018777:Multiple Chemical Sensitivity / Q000150:complications / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects*
D002211:Capsaicin