Idiopathic Anaphylaxis is a constellation of symptoms that include one or more of the following: angioedema, urticaria, gastrointestinal abnormalities, and decreased blood pressure without any recognized external trigger. Gabapentin, an anticonvulsant drug, has been used in different conditions associated with chronic neuropathic pain and pruritic disorders. Because neuropathic pain and pruritus share similar pathogenic mechanisms, neuropathic analgesics like gabapentin have been shown to be effective therapeutic options.
We present a 29 year old female patient with biphasic idiopathic anaphylactic reactions, with accompanying angioedema, urticaria, severe abdominal pain, and diarrhea. The angioedema attacks occurred in laryngeal, facial, and upper extremity regions. Her lab results show normal complement, tryptase levels, and stool culture, and bone marrow biopsy was negative for systemic mastocytosis. Frequency of attacks ranged from 1 to over 20 times a day. Frequency and unpredictability of attacks prompted her to switch to a liquid elemental diet. She was unresponsive to cromoglicic acid, extended-release morphine, hydromorphone, and fentanyl, and only responded to IM/IV epinephrine during the attacks.
We placed the patient on gabapentin 300 mg 4 times daily and within 2 days, she reported 90% resolution of gastrointestinal pain, and returned to a normal diet without anaphylactic episodes.
Gabapentin therapy appears to have been beneficial in the treatment of idiopathic anaphylaxis, including abdominal pain and angioedema. Additional studies investigating the mechanism by which gabapentin mediates pain, autonomic and mast cell responses are needed.