(This delay in appropriate pain management can be a result of insurer-mandated or legally-required step therapy, or merely overly-cautious prescribing on the part of sufferers doctors. )The combination of Cymbalta (duloxetine) and Lyrica (pregabalin) has also proven to be useful in controlling pain, but many EM patients have found this combination has side effects that they are unable to tolerate. Epidemiology
Only a small number of studies that have investigated the prevalence of EM, with four studies conducted to date. The mean of all the studies combined results in an EM estimation incidence of 4.7/100,000 with a mean of 1 : 3.7 of the male to female ratio, respectively.In 1997 there was a study conducted in Norway that estimated that the annual incidence of 2/100,000, with a 1 : 2.4 male to female ratio in this study
population, respectively. In 2009 there was a population-based study of EM in the USA (Olmsted County, Minnesota), that reported that the annual incidence was 1.3/100,000, with a 1 : 5.6 male to female ratio in this study population, respectively. The incidence in this study of primary and secondary EM was 1.1 : 0.2 per 100 000 people per year, respectively. A study of a single centre in the south of Sweden in 2012, showed the overall annual population-based incidence was 0.36/100,000. In New Zealand (Dunedin) a study estimated that in 2013 the incidence of EM is 15/100,000, with a 1 : 3 male to female ratio in this study
population, respectively.
L858F mutant channels, however, are activated at more depolarized potentials when cooled than at normal body temperature. At 16 °C the activation V½ of the mutant channel is only 4.6mV more hyperpolarized that wild-type versus 9.6mV more hyperpolarized at 35 °C. Fast inactivation is affected in a similar manner in both wild-type and L858F mutant channel and is, thus, unlikely to contribute to symptom resolution due to cooling. While such cooling is unlikely to affect neuronal cell bodies, axons and termini express NaV1.7 and are present in the skin. Diagnosis
Erythromelalgia is a difficult condition to diagnose as there are no specific tests available. However, reduced capillary density has been observed microscopically during flaring; and reduced capillary perfusion is noted in the patient. Another test that can be done is to have the patient elevate their legs, and note the reversal (from red to pale) in skin color. Tests done at universities include quantitative sensory nerve testing, laser evoked potentials, sweat testing and epidermal sensory nerve fiber density test (which is an objective test for small fiber sensory neuropathy). Due to the aforementioned factors, patients may face delays in diagnosis.Once it has been established that it is not secondary erythromelalgia — see below — a programme of management can be put in place.Some diseases present with symptoms similar to erythromelalgia. Complex regional pain syndrome (CRPS), for instance, presents with severe burning pain and redness except these symptoms are often unilateral (versus symmetric) and may be proximal instead of purely or primarily distal.