Erythromelalgia is a condition where the feet or the hands are burning hot without an apparent reason. Unfortunately, it can be a very frustrating condition. Often it takes a long time to make the diagnosis. And once you know the diagnosis, finding a treatment that works can be difficult.
Erythromelalgia Symptoms
The main symptom is red extremities that feel extremely hot. The discomfort can be so bad that a person will go to great lengths to get relief. I have seen patients place their hands and feet in buckets of ice water. And I have known more than one person who would only be able to sleep if they were under an air conditioner with the vents pointing at their feet.
Diagnosis
The symptoms should lead to the diagnosis. The problem is that many doctors don’t know about this condition. Another roadblock is that symptoms can be intermittent. So it can prove hard to show them to an expert. For this reason, sometimes, testing blood flow to the hands and feet with and without rewarming can be helpful. This test is called pulse volume recordings with photoplethysmography. The photoplethysmography is the part where you trace blood flow to the fingers and toes.
Making matters worse, there are some conditions that might look a bit like erythromelalgia. This can be confusing when we are trying to make the diagnosis. The classic example is neuropathy. It can be hard to distinguish small fiber neuropathy from erythromelalgia sometimes.
Sometimes erythromelalgia is clumped together with Raynaud’s disease. I always found that weird. To me, these conditions represent opposites. On the one hand, erythromelalgia flares when a person is exposed to heat or exercise. On the other hand, Raynaud’s symptoms are worse during the cold.
The symptoms of erythromelalgia usually start at a young age. But it can be a cause for night leg pain in seniors.
What Causes Erythromelalgia?
The cause is not really clear. Also, there is likely more than one cause. But there are still a few things we can say about the cause. First, there is primary erythromelalgia. Here, the cause is likely specific mutations. For instances, there are reports of a gain of function mutations in families with prevalent symptoms. The mutation was in the gene that encodes the protein Nav1.7 (it is of course, the SCN9A gene). This protein is a sodium channel that operates in nerves that conduct pain sensation.
But most erythromelalgia cases will be secondary. Here, there is probably considerable overlap with small-fiber neuropathy. In fact, testing that focused on the ability to regulate sweat, temperature and blood flow in the microvasculature have shown abnormalities.
Erythromelalgia Treatment
It is often hard to find treatment that works. First, there is cooling. As I wrote, patients will go to great lengths to cool their extremities. In fact, cold-related damage is a complication of erythromelalgia because patients will expose themselves to unhealthy cold. Some patients will present with frank trench-foot, because they immerse their legs in cold water for prolonged periods of time.
Next, there is overlap with symptoms of neuropathy leg pain. And, as I wrote, there is evidence that the small nerve fibers are involved in the secondary types of disease. So neuropathy treatment is a logical approach. Still, in practice data are limited and from what we know the response to treatment is variable.
There are also specific treatments. One such treatment is a roller with a combination of amitriptyline and ketamine. Some preparations include lidocaine. A specialty compounding pharmacy needs to make it to order. Unfortunately, it is not available “off the shelf”.
Sometimes treatment will be condition specific. For instance, if a patient has erythromelalgia as part of polycythemia vera, then we consider aspirin.
Other Therapies
The therapeutics I wrote about above are the most common that we use. But, I have seen publications focusing on other therapies. Non-steroidal anti-inflammatory agents do not work. There are two tiny trials with prostaglandin analogs (iloprost and prostacyclin) that have shown promise. I am not sure I understand the mechanism there, because these medications actually dilate arteries. Similarly, people have tried calcium channel blockers such as amlodipine to treat erythromelalgia. The idea is basically the same as with prostaglandins – to affect the vasoactive components of the condition.
There are case-reports of many other medication groups. For instance, anticonvulsants, beta-blockers, immunosuppressants, nicotinic acid and pain medications such as opioids.
Sympathectomy
Sympathectomy is a logical approach to treat patients who have a combination of vasomotor and sensory disturbances. In fact, we use sympathectomy for patients with refractory Raynaud’s, or other causes of digital ischemia. So, it makes sense to attempt sympathectomy in erythromelalgia. Sympathectomy can be pharmacological (with botululinum toxin) or surgical. Spinal cord stimulation is sometimes used for erythromelalgia leg pain with the same logic.
Block Sodium Channels
People have also tried to block the sodium channel that we believe is in the center of the syndrome (the Nav1.7). Unfortunately, even though this approach makes sense, to date, it has proven challenging to find a blocker that actually helps patients. Similarly, it makes sense to offer non-specific sodium channel blockers. Part of lidocaine’s mechanism is through sodium channels. And we know it can help with erythromelalgia leg pain. Other potential medications that work this way include carbamazepine and oxcarbazepine.
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