Saturday, July 31, 2010

Heat Stroke -- NOT!

I've seen 2 patients this summer misdiagnosed as "heat stroke" who actually had a "stroke stroke".

Heat Stroke

This is an unfortunate nomenclature which has nothing to do with strokes as an ischemic problem in the brain. What is happening in heat stroke is that you are exposed to heat for a prolonged period, and after a certain amount of time, your body's coping mechanisms break down, for one thing, your sweat glands peter out. Since
sweating is one of the primary ways that your body copes with heat, this leads quickly to a rise in body temperature. The other issue with temperature control is that it has its limits as well.

Your brain has something like a thermostat that reacts to body temperature.

This graph to the right in all of its imprecision is meant to illustrate how the brain responds. The "set point" of your brain is this trough in the middle of this curve. So whether your body temperature is going up or going down, to a certain extent your body will respond. But the important thing to see is that beyond some limit, that
response actually diminishes, so when body temperature gets too high or too low, there is a decompensation and associated dropoff in whatever response your brain has to a temperature which is too high or too low. So above or below a certain point, temperature continues to rise or fall. As we get older, the graph gradually flattens, which explains why the elderly are at higher risk for both hypothermia and hyperthermia.

The key elements of diagnosing heat stroke are an excessively high temperature and the absence of sweating, along with other physiologic results of hyperthermia.

If you do not measure an abnormal temperature, then the brain should be functioning normally. If it isn't, then you need to look further. Needless to say, if an MRI had been done in either of these patients, a stroke (as in stroke stroke) would have been diagnosed immediately.

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