Board Review: Dermatology
30 year old male with past medical history of asthma p/w rash onset one week ago. Rash has been worsening throughout the past week. It was initially isolated to the upper extremities but now has spread to the legs as well. It is described as “itchy”. Patient has not tried any medication for symptoms. Denies new medications, detergents, soaps, lotions. Patient lives at home with two roommates who are asymptomatic. The patient is sexually active with one female partner and they do not use any form of contraception. He states the day symptoms started he was dirt biking with friends. Denies any drug or alcohol abuse. Vitals: HR 90, BP 134/78, RR 14, O2 98%, Temp 98.5F. On exam you see:
What is the most appropriate treatment?
A. Topical Permethrin
B. Bactrim and Keflex
E. Acyclovir and Gabapentin
Answer- Prednisone. This patient is presenting with poison ivy dermatitis after exposure while dirt biking in the woods. The plant the patient was exposed to is in the toxicodendron family. These plants typically have three leaves on branches from a single stem. The phrase “leaves of three, let them be” is helpful in remembering to avoid these plants. Urushiol is the substance that induces an allergic reaction. Specifically, this is a type IV hypersensitivity reaction. Another term for this is cell-mediated reaction. These reactions are typically delayed (24-48 hours) and occur after the patient has already been desensitized to the toxin. However, urushiol is so potent that it may cause a reaction on initial exposure. It is transmitted through contact and causes an intense, erythematous, pruritic, linear rash. Urushiol binds the stratum corneum layer of the skin and can remain active for up to three weeks. Patients should avoid scratching as they can continue to spread the toxin, as seen in the case above. Washing gently with soap and water very quickly after exposure can help prevent the spread of the toxin. The treatment of this exposure is typically oral steroids- prednisone 1mg/kg/day up to 60mg/day. There are no clear guidelines regarding duration of steroids but up to a 21 days taper can be considered (60mg first week, 40mg second week, 20mg third week) and has been shown to decrease the need of symptomatic medications . Topical steroids can be used in small amounts but should be avoided on face/hands as they can lead to skin atrophy. Antihistamines (topically or orally) are not particularly helpful in treating the reaction as it is not a histamine based reaction, however, their sedating properties help make the patient more comfortable. Most importantly these patients should be counseled on the duration of symptoms and possible co-infections due to open wounds.
For more information see this EM daily post:
Curtis G, Lewis AC. Treatment of Severe Poison Ivy: A Randomized, Controlled Trial of Long versus Short Course Oral Prednisone. Journal of Clinical Medicine Research. 2014; 6(6): 429-434