You can put me down as a contrarian on this thread.
Firstly, to the OP, traveling in an airplane does not constitute exposure to altitude, it constitutes exposure to the atmosphere of a pressurized cabin. That, for reasons that follow, might be what is producing a benefit.
Secondly, I am sceptical that high altitude exposure (and its attendant thin air) is beneficial to MS. To experience immediate relief of symptoms as described, likely points more to conditions that mask nerve damage than to nerve regeneration. I just can’t see nerve regeneration taking place that quickly. Generally, the higher one’s core body temperature is the more likely it is that they will notice nerve damage, because the nerves are having to carry more electricity to get the job done. That’s why my limp gets much worse after exercise or when I’m running a fever. That doesn’t mean that my MS is worse (conversely, I happen to think that exercise is beneficial), it simply means that I am exposing damage. The opposite may be said about walking around in cooler high altitudes.
Moreover, the theory that altitude is good for MS contradicts numerous epidemiological studies that have shown that the incidence and prevalence of MS is much higher inland than in coastal areas and is lowest in the tropics. For instance, the region in Canada with the highest prevalence of MS is the Crowsnest Pass in Alberta (elevation 4,455 ft) at 217 per 100,000:
Indeed, there is a very illuminating article on this subject by someone who looked at the epidemiological data and concluded that the thinner air in high altitude regions may contribute to MS. Even more startling is that he comes to a CCSVI conclusion from looking at this data pre-publication of Zamboni’s research. A link to his full article can be found here:
The author was particularly struck as to why Colorado has such a high incidence of MS and reasoned that it likely has to do with oxygen, since oxygen is thinner at higher elevations. The lower prevalence in coastal regions can be explained by denser air, higher prevalence in cities because of polluted air, and higher prevalence in smokers by poor oxygenation. I particularly enjoyed this quote:
Question #9 and 11 are best answered and best understood together through the insights of Peter Good: “Two signs that endothelial nitric oxide may be chronically depleted in multiple sclerosis are that patients tend to be very heat-sensitive, and their platelets are sticky. Sensitivity to stress may reveal depletion of the parasympathetic transmitter neuronal nitric oxide. Other reasons to suspect endothelial nitric oxide depletion in multiple sclerosis are apparent deficiencies of sex hormones, magnesium, and zinc. Estrogen, testosterone via estrogen, and magnesium all utilize endothelial nitric oxide, the primary endogenous vasodilator, to relax vascular smooth muscle. The (most simple and straightforward explanation) cause of multiple sclerosis might be that too little blood in arteries and arterioles leads to vasospastic symptoms, while too much blood in veins and venules leads to blood-brain barrier leakage and lesions.” A recent Nobel Prize based upon L-arnithine and nitric oxide gas in the blood being a "trigger" for the body seems to offer a promising area for further study. In any case, Oxygen's potentially primary role would be in harmony with this data.
To the above, I would like to add that simple reference to elevation only tells part of the story. My fondness of drag racing and horsepower lead me to learn about “density altitude”. This is the effective altitude of an area by looking at how dense the air is by reference to altitude, temperature, and atmospheric pressure. What I discovered is though the elevation of my locale is relatively low, for most of the summer, with high temperature and low humidity; its density altitude was the same on most days as Calgary (contributing to slower ¼ mile times). In our frigid cold winters, however, the density altitude is often many feet below sea level. Cold air = oxygen rich air.
Referring back to epidemiological studies, MS attacks more frequently occur in the spring and are the least common in winter (all my attacks happened in the spring):
Some researchers suggest that multiple sclerosis is common in temperate regions due to the seasonal fluctuations in daylight affecting body chemistry. Research has shown that both disease onset and relapses are more common in the springtime and least common in the winter [Jin et al, 2000]. Levels of vitamin D3, melatonin and other biochemicals have all been shown to vary with the seasons and some of these have been shown to be immunologically or neurologically active [Embry et al, 2000, Timonen TT, 1999; Hayes, 2000, Nelson et al, 2001, Prendergast et al 2001].
Using the CCSVI model, perhaps in winter with its low UV, our CCSVI prone veins are susceptible to stenosis due to low Vitamin D absorption, but is masked by being able to breath oxygen-rich winter air. Once spring rolls around, we are exposed to thinner dry air as the temperature warms and or veins don’t adapt.
Perhaps CCSVI will ‘breath’ new life into oxygen therapy for MS?