This epidemic form of erythromelalgia has been viewed as a different form of non-inherited primary erythromelalgia and affects mainly teenage girls in middle schools. The disease is characterized by burning pain in the toes and soles of the feet, accompanied by  foot redness, congestion, and edema; a few patients may have fever, palpitations, headache, and joint pain. In the 1987 epidemic in Hubei, 60.6% of patients had a common cold before the onset of erythromelalgia and 91.2% had pharyngitis. Billing codes systems and other systems
Erythromelalgia can be found in several billing codes systems and other systems. Erythromelalgia is generally classified as a disease of the circulatory system, falling under the class of other peripheral vascular disease, as the following two billing code systems will show:

ICD-9-CM According to the ICD-9-CM database (International Classification of Diseases, Ninth Revision, Clinical Modification), Erythromelalgia is listed under Diseases of the Circulatory System and is identified by  number 443.82. ICD-10-CM According to the ICD-10-CM database (International Classification of Diseases, Tenth Revision, Clinical Modification), Erythromelalgia is listed under Diseases of the circulatory system and is identified by I73.81. Mesh According to the MESH database (Medical Subject Headings), Erythromelalgia is classified under the unique ID number of D004916. OMIM According to the OMIM database (NCBI - Online Mendelian Inheritance in Man), Primary Erythromelalgia is listed under the number: 133020.
This last study has an estimation that is at least ten times higher than the prevalence previously reported. This study recruited individuals based on self-identification of symptoms (after self-identification, patients were invited for an assessment of an EM diagnosis), instead of participants that are identified through secondary and tertiary referrals as in the other studies. Prevalence in China
Epidemic EM appears quite common in female middle school students of southern China, most likely due to a sharp decline in temperature following by a rapid increase of temperature. It has been postulated that epidemic erythromelalgia might be related to a poxvirus (ERPV) infection. The disease was characterized by burning pain in the toes and soles of the feet, accompanied by foot redness, congestion, and edema; a few patients had fever, palpitations, headache, and joint pain. 60.6% of patients had a common cold before the onset of erythromelalgia and 91.2% had pharyngitis. For temperature-related theory, the acral (foot and hand) small superficial arteries intensely constrict and dilate during the sharp decline of temperature, whereas a sharp increase of temperature, the intense expansion of capillaries irritate the nerve endings around, and thus lead to syndromes including (first and second degree) burning pain, increased temperature, erythema and swelling. History
The first reported case was in 1878 by Silas Weir Mitchell who suggested the term erythromelalgia to describe a syndrome of red congestion and burning pain in the hands and feet. He distinguished it from the painful red limbs seen in some patients with gout or rheumatoid arthritis.