From OMIM
'Primary erythermalgia' is an autosomal dominant disorder characterized by childhood or adolescent onset of episodic symmetrical red congestion, vasodilatation, and burning pain of the feet and lower legs provoked by exercise, long standing, and exposure to warmth. Relief is obtained with cold (Michiels et al., 2005). The severity of the disorder may progress with age, and symptoms may extend over a larger body area, such as over the ankles and lower legs, and become constant (Mandell et al., 1977). Waxman and Dib-Hajj (2005) provided a review of primary erythermalgia. Although 'primary' or 'familial erythromelalgia' are sometimes used as alternative terms for primary erythermalgia (Waxman and Dib-Hajj, 2005), secondary erythromelalgia is a distinct acquired disorder associated with thrombocythemia or myeloproliferative disorders. It has relatively late onset and symptoms are caused by platelet aggregation in end-arteriolar circulation, leading to ischemia and symptoms (Michiels and van Joost, 1990). Treatment with aspirin, which irreversibly inhibits platelet cyclooxygenase activity, affords relief from acquired erythromelalgia (Michiels et al., 1984; Drenth et al., 1996). Similarly, acquired erythromelalgia vanishes with lowering the platelet count to normal with chemotherapy (Michiels et al., 1985). Van Genderen et al. (1993) emphasized the distinction between hereditary erythermalgia and acquired erythromelalgia. In primary erythermalgia, the burning pain, redness, and warmth of feet and lower legs, with relative sparing of the toes, are easily provoked by warmth and exercise. In contrast, in acquired erythromelalgia the burning pain and red congestion preferentially involves one or more toes or fingers or sole of the forefoot (Michiels and van Joost, 1990). Van Genderen et al. (1993) noted that 3 of the 5 patients reported by Smith and Allen (1938) were not consistent with the diagnosis of primary erythromelalgia because the symptoms were relieved promptly by aspirin, consistent with acquired erythromelalgia. Small Fiber Neuropathy Small nerve fiber neuropathy (SFNP) is a relatively common disorder of thinly myelinated and unmyelinated nerve fibers characterized clinically by adult onset of neuropathic pain, often of a burning quality, and autonomic symptoms. Affected individuals have reduced intraepidermal nerve fiber density affecting the small diameter nerve fibers; large diameter fibers are spared (summary by Faber et al., 2012).  http://www.omim.org/entry/133020

From MedlinePlus Genetics
Erythromelalgia is a condition characterized by episodes of pain, redness, and swelling in various parts of the body, particularly the hands and feet. These episodes are usually triggered by increased body temperature, which may be caused by exercise or entering a warm room. Ingesting alcohol or spicy foods may also trigger an episode. Wearing warm socks, tight shoes, or gloves can cause a pain episode so debilitating that it can impede everyday activities such as wearing shoes and walking. Pain episodes can prevent an affected person from going to school or work regularly.

The signs and symptoms of erythromelalgia typically begin in childhood, although mildly affected individuals may have their first pain episode later in life. As individuals with erythromelalgia get older and the disease progresses, the hands and feet may be constantly red, and the affected areas can extend from the hands to the arms, shoulders, and face, and from the feet to the entire legs.

Erythromelalgia is often considered a form of peripheral neuropathy because it affects the peripheral nervous system, which connects the brain and spinal cord to muscles and to cells that detect sensations such as touch, smell, and pain.  https://medlineplus.gov/genetics/condition/erythromelalgia