Toxin impact can do it, low selenium or vitamin E can do it, and if you ran a regular thyroid then you might want to have Michigan State do a full thyroid panel or have Dr Dodds in CA do one as a full panel shows a lot more than the standard one done in local labs. Sometimes the CPK is way off due to thyroid.
A blood panel rerun might be a reasonable thing to do also see if the reading was accurate.
I do think seeing an internal medicine specialist would be a good next move.
Its possible a cancer, a malabsorption issue, a toxin or something else causing muscle wasting is triggering the high CPK.
My suspicion is, if it can be figured out, its not going to be something 'common'.
http://www.isrvma.org/article/54_3_7.htm
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