Multiple sclerosis patients are sensitive to heat. But why? Research on this topic abounds.
Quoting the journal of applied physiology :
“…The precise mechanisms for impaired neural function in demyelinated axons due to increases in temperature are not completely understood but are likely due to a combination of structural and physiological changes within axons in the CNS (75). With demyelination, increases in temperature can affect the propagation of action potentials. Increased temperature may also influence the electrical properties of the nerve fiber by increasing the refractory period (partly mediated by potassium channel activation and sodium channel inactivation), which surpass the action potential-generating processes (sodium channel activation…”
I want know to bring your attention to the excellent article on cooling devices for MS people that Julie Stachowiak posted in her MS newsletter at about.com 
Her post was about vests, mist generators and other devices.
Focusing on the vests, the cooling mechanism is by
- icepack, which focuses on the the fact that melting of various substances absorbs energy.
- evaporation, another phase change, also absorbs energy to occur
- active cooling, the more complex of cooling approaches. It uses thermo-electric and other active refrigeration processes
From Gizmag, here is an example of cooling vests:
These vests are not only for the disabled, but some are used by firefighters , race car drivers , etc….
An interesting discussion on such vests can be found on University of Maryland’s project 
Extreme versions of such vests are designed for military use, probably with a military price tag. Such are the vests by the RIF Corp
The impact of thermal regulation of peoples’s health was also noticed by the home building industry . We throw in their entry on HVAC and Home Health for general good measure.
Hope this helps!
- Journal of applied Physiology ; Thermoregulation in multiple sclerosis ; 2010
- Multiple Sclerosis Cooling Products ; Julie Stachowiak ; about.com
- University of Maryland’s ; Cooling Vest Project
- Riff Corp ; Thermoelectric cooling vests
- Journal of Indoor Environmental Quality ; “Thermoregulatory dysfunction linked to multiple sclerosis, migraine headaches, epilepsy, stress and anxiety, and schizophrenia” ;2011
- Health Heating ; “Current State of the Science: Health Effects and Indoor Environmental Quality”; 2007