Paroxysmal Extreme Pain Disorder (PEPD)
Paroxysmal extreme pain disorder (PEPD), which was originally named familial rectal pain syndrome, is a rare disorder whose most notable features are pain in the lower jaw, eyes, and rectal areas as well as flushing. PEPD often first manifests at the beginning of life, perhaps even in utero, with symptoms persisting throughout life. Sometimes the pain is associated with flushing (bright red) and may be limited to one side of the body. This disorder is allelic, caused by mutations in the voltage-gated sodium channel NaV1.7 encoded by the gene SCN9A. PEPD also shares a genetic basis with channelopathy-associated insensitivity to pain, which causes hypo-sensitivity to pain. Only 14 families in the entire world have so far been identified with this inheritable disorder.
Carbamazepine is usually at least partly effective in reducing the number and/or severity of attacks in the majority of PEPD patients. High doses of this drug may be required. While other anti-epileptic drugs, gabapentin and topiramate, have limited effect in some patients, they have not been shown to be generally effective. Opiate derived analgesics are also largely ineffective, with only a few cases of beneficial effect.