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.
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. Myeloproliferative disease
Hypercholesterolemia
Autoimmune disorder
Small fiber peripheral neuropathy
Fabrys disease
Mercury poisoning
Mushroom poisoning
Obstructive Sleep Apnea
Sciatica
Some medications, such as fluoroquinolones, bromocriptine, pergolide, verapamil, and ticlopidine

Treatment
For secondary erythromelalgia, treatment of the underlying primary disorder is the most primary method of treatment. Although aspirin has been thought to reduce symptoms of erythromelalgia, it is rare to find evidence that this is effective. Mechanical cooling of the limbs by elevating them can help or managing the ambient environment frequently is often necessary constantly as flares occur due to sympathetic autonomic dysfunction of the capillaries. The pain that accompanies it is severe and treated separately (the pain is similar to CRPS, phantom limb or thalamic pain syndrome). Patients are strongly advised not to place the affected limbs in cold water to relieve symptoms when flaring occurs. It may seem a good idea, but it precipitates problems further down the line causing damage to the skin and ulceration often intractable due to the damaged skin. A possible reduction in skin damage may be accomplished by enclosing the flaring limb in a commonly available, thin, heat transparent, water impermeable, plastic food storage bag. The advice of a physician is advised depending on specific circumstances.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.