Multiple chemical sensitivity: On the scent of central sensitization

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. PURPOSE: 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 60min 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