@CarterDK does mexiletine work at all if it is not primary?
I’m not sure. Primary erythromelalgia has an established cause related to sodium channel dysfunction (mexiletine is a sodium channel blocker). What causes secondary erythromelalgia is not understood.
That’s what I figured. Thanks. That’s like the one gene mutation I don’t have 
Might still be worth a try, if your doctor is willing. I was never directly tested for the mutation. My doctor presumed I had primary erythromelalgia and thought mexiletine gave me the best chance for improvement.
Side note: The disordered temperature regulation I spoke about in this thread 2 years ago has resolved. My legs now stay a consistent, normal body temperature throughout.