In other cases symptoms emerge full blown with onset.Epidemic erythromelalgia 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. Cause
In general, erythromelalgia seems to consist of neuropathological and microvascular alterations. How this occurs in secondary erythromelalgia is poorly understood and may be specific to the underlying primary condition. Primary conditions that have been shown to elicit erythromelalgia are listed in diagnosis, below.Primary erythromelalgia is a better understood autosomal dominant disorder. The neuropathological symptoms of primary erythromelalgia arise from hyperexcitability of C-fibers in the dorsal root ganglion. Specifically, nociceptors (neurons responsible for the sensation and conduction of painful stimuli) appear to be the primarily affected neurons in these fibers. This hyperexcitability results in the severe burning pain experienced by patients. While the neuropathological symptoms are a result of hyperexcitability, microvascular alterations in erythromelalgia are due to hypoexcitability. The sympathetic nervous system controls cutaneous vascular tone and altered response of this system to stimuli such as heat likely results in the observed microvascular symptoms. In both cases, these changes in excitability are typically due to mutation of the sodium channel NaV1.7.
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.