I have erythromelalgia, and anything heat related makes it worse and makes my feet turn red and sometimes even purple. It is a neurovascular disease, so there is Small blood vessel involvement, and small fiber nerve pain. Tests for neuropathy come back negative. Vein and artery test come back normal. There was no test for erythromelalgia, But I typed up in detail all my symptoms and how cold temporarily relieves the pain, and all the tests I have had, and what I have tried, and a good neurologist finally diagnosed me with erythromelalgia. All my tests for everything come back negative. There is no test for erythromelalgia…. it is just a matter of getting tested to rule out other things. And gathering of all the symptoms, what relieves it, what aggravates it. Etc