Erythromelalgia. Any experience of this condition?

My OH occasionally suffers from very red, painful, swollen areas on some of his toes, which can last two or three weeks, sometimes longer. He says they feel sunburnt, although that isn’t the cause. He has been to his GP in the past, who said he thought it could be gout, but the blood test revealed that it wasn’t, I’ve researched it and think that it could be Erythromelalgia and wondered if anyone else is familiar with this? OH has since just treated it by using cool gel packs. He also has Erythrocytosis, which he’s had for a few years and takes medication, with regular blood tests. It could be connected. He’ll go back to the GP, as it could also be triggered by certain foods. He thinks it could be rhubarb, as he was eating quite a lot when I was on holiday!