New research into multiple chemical sensitivity shows that the brains of sufferers respond more easily and more strongly to stimuli than those of healthy individuals, supporting the 'central sensitization' theory as an explanation for the illness.
Multiple Chemical Sensitivity (MCS) is a chronic condition in which those affected experience an array of non-specific symptoms including headaches, fatigue, weakness, dizziness, cognitive dysfunction, and a general feeling of being unwell, when exposed to minute amounts of chemical triggers such as synthetic fragrances and industrial pollution.
The few scientists and physicians who have been actively investigating this disabling and increasingly common condition over the past few decades have long suspected that an initial sensitization of the brain might result in neurons subsequently firing when exposed to levels of stimuli that would normally be ignored. This would translate into someone affected by MCS having an unusually high level of brain activity when exposed to triggering chemicals and experiencing a host of neurologically-based symptoms such as those mentioned previously.
Now, investigators from The Danish Research Centre for Chemical Sensitivities at Copenhagen University Hospital, Denmark, have shown this is indeed the case by comparing MCS patients to healthy volunteers using a comprehensive set of measures, referred to inclusively as quantitative sensory testing (QST), to assess brain sensitivity and activity.
The study involved 15 MCS patients without any comorbid overlapping condition (e.g. fibromyalgia, chronic fatigue syndrome ) and 15 healthy individuals matched for factors such as sex and age.
The researchers used injections of capsaicin as a stimulatory challenge in order to study the responses of all participants, both those who suffered from MCS and those who didn't. Capsaicin is a chemical found in chili peppers that is an irritant and is responsible for the sensations of burning, and even pain, experienced when spicy foods are consumed.
Other stimuli such as pressure and heat were also used to measure pain thresholds in all participants.
It was found that MCS patients experienced a significantly greater degree of pain as a result of the capsaicin challenge compared to their healthy counterparts.
Several other measures were also consistently higher in the MCS patients although no difference in pain thresholds for pressure or heat were found.
The investigators concluded that: "Increased capsaicin-induced secondary punctate hyperalgesia was demonstrated in MCS patients without comorbid, overlapping disorders, suggesting facilitated central sensitization in MCS."
Essentially what they are saying here is that MCS patients' brains are more active than those of healthy individuals when exposed to external stimuli. Their study therefore validates MCS as a genuine physical illness and points to hypersensitivity of the brain to chemicals as the major mechanism behind symptoms experienced.
Source: Tran MT Arendt-Nielsen L Kupers R Elberling J (2012) Multiple chemical sensitivity: On the scent of central sensitizationInternational Journal of Hygiene and Environmental Health http://dx.doi.org/10.1016/j.ijheh.2012.02.010
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