Case history

A 38 year old Asian American woman comes to the office with a red painful ankle. The patient states that she sprained her right ankle two days ago by inverting it while walking. She believed it to be a minor sprain and did not go to a physician. However, she did apply a Chinese medicine patch that was given to her by her mother, who recently emigrated from China. The patient applied the medicine that was impregnated in a patch to the anterior medial and lateral portions of her ankle, leaving the posterior portion uncovered. The following day the patient broke out in a red and painful rash with blisters. The patient denies any fever or systemic symptoms. She does not know the ingredients in the medication. The rash is painful and the lesions made it painful to walk. Figures 1 and 2 show the patient's ankle at the time of her first visit to the office. The erythema has a well demarcated border, which has been traced by the doctor's pen in both figures. The skin is also covered with many small vesicles (<5 mm in diameter) and at least five large intact bullae (>5 mm in diameter).

Questions

1. What is the most likely diagnosis?
2. How would you confirm this diagnosis?
3. What features of this rash distinguish it from other conditions in the differential?
4. How would you manage this patient?

Answers

1. Severe contact dermatitis to topical Chinese medicine.
2. Recent history of exposure to allergen and physical examination revealing a classic pattern of contact dermatitis - erythema with a well demarcated border, vesicles and bullae.
3. Lack of a linear pattern distinguishes this from a contact dermatitis to a plant, and the presence of vesicles makes an irritant dermatitis less likely.
4. Discontinue use of Chinese medication; prescribe cold compresses and topical steroid preparations. If the patient shows no improvement after a two day follow up, oral prednisone should be considered. (In this actual case, the patient was given a two week course of prednisolone starting with 60 mg daily and tapering down to 5 mg daily. The patient responded rapidly and the condition fully resolved.)

Discussion

Allergic contact dermatitis is a delayed hypersensitivity reaction that occurs after exposure to an antigenic substance. This dermatitis usually appears as an acute vesicular dermatitis within a few hours to 72 hours after contact. The course peaks within 7 to 10 days and resolves within 21 days if there is no repeat exposure. This patient has a severe contact dermatitis to the topical Chinese medicine. It is possible that the patient was exposed to this substance as a child in China. Although this patient reports no previous occurrences of contact dermatitis, the recent history and physical examination represent a classic pattern for contact dermatitis. Therefore no further testing is indicated. Because the ingredients of the Chinese medicine are unknown, it is difficult to pinpoint the exact allergen causing the contact dermatitis.

Differential diagnosis

The differential diagnosis includes irritant dermatitis and contact dermatitis due to other substances. The prototypical contact dermatitis is poison oak, ivy, or sumac. These conditions can look similar and are often distinguished by the line of vesicles that can occur from brushing against one of the plants of the Anacardiaceae family. Also the linear pattern occurs from scratching oneself and dragging the oleoresin across the skin with the fingernails. In the case presented here, the erythema and vesicles are widespread and show no linearity. Although irritant dermatitis may look like contact dermatitis it is not caused by an immunological mechanism. The causative substance in irritant dermatitis (a harsh detergent, for example) is purely irritating to the skin and does not serve as an allergen. In patch testing strong allergic reactions are vesicular whereas irritant reactions show a non-vesicular erythema.

Treatment

The aetiological agent must be identified and removed. Cold wet compresses may be prescribed for the open areas where bullae and vesicles have broken open. Compresses are valuable to relieve symptoms during the acute blistering stage. They may be applied for 15 to 30 minutes several times a day. A strong topical corticosteroid may be used to treat the severe inflammatory reaction. Topical steroids are not effective in penetrating blisters but may be very valuable for the surrounding areas. Oral antihistamines may be given for itching. Aveeno baths may be used to soothe the area and control itching. If use of systemic steroids is indicated (in severe cases or those refractory to topical steroids), there is a choice of oral prednisolone or an injection of triamcinolone acetonide (40 mg intramuscularly). Oral prednisolone doses may vary widely. A simple dose regimen is 20 mg twice a day for at least six days.¹ Antibiotic therapy is required for cases involving secondary infections.

1. Habif T. Clinical Dermatology: a color guide to diagnosis and therapy, London: Mosby, 1996. 3rd ed.