from opioid drugs. Opana ER has been found to be effective for many in the US, whilst in the UK slow-release morphine has proved to be effective. These powerful and potentially-addictive drugs may be prescribed to patients only after they have tried almost every other type of analgesia to no avail. (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. 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