There are 2 types of Erythromelalgia (EM). Primary and Secondary. Primary EM is genetic and can be diagnosed with genetic testing. If you didn't develop symptoms until later in life, it is likely secondary to something else, and there is no specific test but is diagnosed based off symptoms and eliminating other possibilities. There isn't a specific type of specialist to diagnose/treat EM. You have to find a specialist that happens to know about EM which can be difficult as many don't know what it is. Your best bet would be either a Rheumatologist, Dermatologist, or Neurologist, but also an Autonomic specialist, Cardiologist, Vascular doc, or Hematologist may have knowledge on what EM is. There is a website that provides a list of specialist familiar with EM. Also, be sure to document everything you can and take pictures of flares.