Product Code Database
Erythromelalgia, or Mitchell's disease (after Silas Weir Mitchell), is a rare vascular peripheral pain disorder in which , usually in the Human leg or , are episodically blocked (frequently on and off daily), then become hyperemic and Inflammation. There is severe burning pain (in the small fiber sensory nerves) and Erythema. The attacks are periodic and are commonly triggered by heat, pressure, mild activity, exertion, insomnia or stress. Erythromelalgia may occur either as a primary or secondary disorder (i.e. a disorder in and of itself or a symptom of another condition). Secondary erythromelalgia can result from small fiber peripheral neuropathy of any cause, polycythemia vera, essential thrombocythemia, hypercholesterolemia, mushroom or mercury poisoning, and some autoimmune disorders. Primary erythromelalgia is caused by mutation of the voltage-gated sodium channel α-subunit gene SCN9A.
In 2004 erythromelalgia became the first human disorder in which it has been possible to associate an ion channel mutation with chronic neuropathic pain, when its link to the SCN9A gene was initially published in the Journal of Medical Genetics. Later that year, in an article in The Journal of Neuroscience, Cummins et al., demonstrated, using voltage clamp recordings, that these mutations enhanced the function of NaV1.7 sodium channels, which are preferentially expressed within peripheral neurons. One year later, in an article in Brain, Dib-Hajj et al., demonstrated that NaV1.7 mutants channels, from families with inherited erythromelalgia (IEM), make dorsal root ganglion (DRG, peripheral and sensory), neurons hyper excitable, thereby demonstrating the mechanistic link between these mutations and pain, thereby firmly establishing NaV1.7 gain-of-function mutations as the molecular basis for IEM. Conversely, in December 2006 a University of Cambridge team reported an SCN9A mutation that resulted in a complete lack of pain sensation in a street performer and some of his family members. He felt no pain, walked on hot coals and stabbed himself to entertain crowds. By 2013, nearly a dozen gain-of-function mutations of NaV1.7 had been linked to IEM. The multi-decades search which identified gene SCN9A as the cause of inherited erythromelalgia is documented in a book by Stephen Waxman, Chasing Men on Fire: The Story of the Search for a Pain Gene.
In rural areas of southern China, outbreaks of erythromelalgia have occurred during winter and spring at 3–5 year intervals among secondary school students. 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.
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.
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, (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 muscle 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. These differences in excitability alterations between the sympathetic nervous system and is due to different expression of other than NaV1.7 in them.
What causes epidemic erythromelalgia in southern China remains unknown although several erythromelalgia-associated poxviruses were isolated from throat swabs of several patients at different counties and from two different seasons.
Since this virus has not yet been isolated from other outbreaks in other parts of southern China to date this putative association needs to be further investigated. The finding of the specific antibody conversion to ATIs of ERPV in patients' paired sera strengthens the evidence for a possible aetiological role of human ERPV in epidemic erythromelalgia.
Some of these mutant channels have been expressed in dorsal root ganglion (DRG) or sympathetic . In DRG neurons expressing the F1449V mutation, a lower threshold is required for action potential creation (93.1 ± 12.0 ampere) than those expressing wild-type channels (124.1 ± 7.4 pA). Furthermore, while DRG neurons expressing wild-type channels only respond with a few action potentials, those expressing F1449V channels respond with a high-frequency train of action potentials. There is a similar effect in DRG neurons expressing the L858H and A863P mutants. Here, there is also a notable change in resting membrane potential, being depolarized by 4-7 volt versus wild-type channel expressing cells. The situation is different, however, in sympathetic neurons expressing the L858H mutation. While L858H expressing sympathetic ganglion are depolarized ~5mV relative to wild-type expressing neurons, their threshold for action potential initiation is notably higher. Furthermore, while current injection of 40pA for 950ms provokes an average of 6 action potentials in sympathetic neurons expressing wild-type channels this stimulation evokes only approximately 2 action potentials with reduced overshoots in sympathetic neurons expressing L858H mutant channels. Further investigation has demonstrated that the differences in response between DRG and sympathetic neurons is due to expression of NaV1.8 in the former. Consequently, expression of NaV1.8 channels in sympathetic neurons also expressing L858H mutant NaV1.7 results in neurons with a depolarized resting membrane potential that nevertheless have a normal action potential threshold and overshoot.
An effective, though not recommended, treatment for erythromelalgia symptoms is cooling of the affected area. Activation of wild-type channels is unaffected by cooling. 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, and termini express NaV1.7 and are present in the skin.
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. Furthermore, attacks triggered by heat and resolved by cooling are less common with CRPS.
Erythromelalgia is sometimes caused by other disorders. A partial list of diseases known to precipitate erythromelalgia is below.
Primary erythromelalgia management is symptomatic, i.e. treating painful symptoms only. Specific management tactics include avoidance of attack triggers such as: heat, change in temperature, exercise or over exertion, alcohol and spicy foods. This list is by no means comprehensive as there are many triggers to set off a 'flaring' episode that are inexplicable. Whilst a cool environment is helpful in keeping the symptoms in control, the use of cold water baths is strongly discouraged. In pursuit of added relief sufferers can inadvertently cause tissue damage or death, i.e. necrosis. See comments at the end of the preceding paragraph regarding possible effectiveness of plastic food storage bags to avoid/reduce negative effects of submersion in cold water baths.
One clinical study has demonstrated the efficacy of IV lidocaine or oral mexilitine, though differences between the primary and secondary forms were not studied. Another trial has shown promise for misoprostol, while other have shown that gabapentin, venlafaxine and oral magnesium may also be effective, but no further testing was carried out as newer research superseded this combination.
Strong anecdotal evidence from EM patients shows that a combination of drugs such as duloxetine and pregabalin is an effective way of reducing the stabbing pains and burning sensation symptoms of erythromelalgia in conjunction with the appropriate analgesia. In some cases, antihistamines may give some relief. Most people with erythromelalgia never go into remission and the symptoms are ever present at some level, whilst others get worse, or the EM is eventually a symptom of another disease such as systemic scleroderma.
Some suffering with EM are prescribed ketamine topical creams as a way of managing pain on a long-term basis. Feedback from some EM patients has led to reduction in usage as they believe it is only effective for short periods. Living with erythromelalgia can result in a deterioration in quality of life resulting in the inability to function in a work place, lack of mobility, depression, and is socially alienating; much greater education of medical practitioners is needed. As with many rare diseases, many people with EM end up taking years to get a diagnosis and to receive appropriate treatment. Research into the genetic mutations continues but there is a paucity of clinical studies focusing on living with erythromelalgia. There is much urgency within pharmaceutical companies to provide a solution to those who suffer with pain such as that with erythromelalgia.
Mild sufferers may find sufficient pain relief with tramadol or amitriptyline. Sufferers of more severe and widespread EM symptoms, however, may obtain relief only 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-addiction drugs may be prescribed to patients only after they have tried almost every other type of analgesic 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.
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.
There was a study done in 2013 where two Vietnamese patients were diagnosed with primary erythromelalgia. Patient A was a 33-year old female diagnosed with primary erythromelalgia at age 30 and suffered from burning and pain in her feet since she was 8 years old (Wu et. al 2013). Patient B was a 16 year-old girl with recurrent severe burning pain of both feet since the age of seven (Wu et. al 2013). A genetic analysis was performed where scientists observed three missense mutations, one familial and two sporadic mutations. The familial mutation changed isoleucine to valine and two missense mutations occurred where a "T" was changed to "C" (Wu et. al 2013). The three mutants involved in the gene were I136V, 1848T, and V1316A (Wu et. al 2013). The study showed that at higher temperatures, the hypersensitivity of the mutant channels were accentuated resulting in disease phenotype such as neuralgia (Wu et. al 2013).
In 1994 Drenth, van Genderen and Michiels distinguished between erythromelalgia and erythermalgia on the basis of responsiveness to aspirin. They established three categories: erythromelalgia (platelet-mediated and aspirin-sensitive), primary erythermalgia, and secondary erythermalgia.
Because of the confusion in terminology, Norton and Zager and Grady classified erythromelalgia in 1998 as either: primary/idiopathic erythromelalgia or secondary erythromelalgia. The primary/idiopathic form of erythromelalgia is not associated with any other disease process and can be either early onset (in children) or adult onset. In their paper they described secondary erythromelalgia as being associated with another disease, often related to a myeloproliferative disorder and has also seen cases of: hypertension, diabetes mellitus, rheumatoid arthritis, gout, systemic lupus erythematosus, multiple sclerosis, astrocytoma of the brain, vasculitis, and pernicious anemia.
The following table shows the history of the nomenclature of Erythromelalgia:
| Silas Weir Mitchell in 1878 |
| Carl Gerhardt in 1892 |
| Thomas Lewis in 1933 |
| L.A. Smith and F.N. Allen in 1938 |
| J. Huizinga in 1957 |
|
|
