Photograph of the legs of a patient with inherited erythromelalgia, showing erythema to the level of the mid-calf. Photograph of the legs of a patient with inherited erythromelalgia, showing erythema to the level of the mid-calf. With increasing ambient temperature, this erythema becomes more extensive. (Reproduced with permission of the International Association for the Study of Pain (IASP) from Segerdahl et al).47 Andreas C Themistocleous et al. Pract Neurol 2014;14:368-379 ©2014 by BMJ Publishing Group Ltd