Review Question - QID 107257

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Porphyria Cutanea Tarda Differential Diagnosis Erythropoietic protoporphyria QID: 107257 (M2.DM.15.4678)

QID 107257 (Type "107257" in App Search)

A 3-year-old boy is brought to his pediatrician by his mother when he developed redness, burning, itching, and exquisite pain all over his arms, lower legs, neck, and face. The mother states that she just recently began taking him to the local playground in the afternoons. She reports that she applied liberal amounts of sunscreen before and during the time outside. She states that they were at the playground for 30 minutes to 1 hour each day for the last 3 days. The patient has experienced prior episodes of redness and pain after being outdoors, but they were relatively minor and resolved within 12 hours. She says his current presentation is much more severe with more exquisite pain than in the past. The patient's vital signs are as follows: T 37.2 C, HR 98, BP 110/62, RR 16, and SpO2 99%. Physical examination reveals edema, erythema, and petechiae over the patient's face, neck, arms, and lower legs. No blistering or scarring of the skin is noted. Which of the following is the best treatment option for this patient's condition?

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Recommend use of a high SPF topical sunscreen

33%

9/27

Begin dexamethasone taper

37%

10/27

Start therapeutic phlebotomy

2/27

Initiate oral beta carotene

11%

3/27

Prescribe chloroquine

2/27

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This patient's presentation is consistent with erythropoeitic protoporphyria (EP). Oral beta carotene may reduce photosensitivity in some patients.

EP is caused by a deficiency of the ferrochelatase enzyme, the final enzyme in the heme biosynthesis pathway. This results in accumulation of protoporphyrin substrate, which manifests clinically as acute cutaneous photosensitivity as well as hepatobiliary disease. The inheritance is termed "pseudodominant", as both autosomal recessive and dominant forms have been identified. It presents with excruciating pain, redness, and swelling of the skin after short-term sun exposure. Blisters, erosions, and scarring are less common.

Sekula et al. review the porphyrias. This group of disorders is caused by inherited defects in the heme synthesis pathway, with each specific disease caused by a unique enzymatic defect and resultant specific elevations of corresponding heme precursors. Photosensitivity in a young adult or child should raise suspicion; other findings may be noted in the skin, teeth, and/or eyes.

Langendonk discusses management of EP. A new treatment, afamelanotide, is currently is currently being studied in Europe. It is an alpha-melanocyte stimulating hormone (alpha-MSH) analog that is administered as a delayed-release subcutaneous implant every 2 months. The drug stimulates production of eumelanin, which blocks visible light penetration, thereby increasing patient tolerance to sunlight and reducing photosensitivity.

Illustration A shows the acute photosensitivity reaction seen in EP. Illustration B summarizes the heme biosynthesis pathway and shows the ferrochelatase enzyme defect in EP.

Incorrect Answers:
Answer 1: Most sunscreens, with the exception of zinc or titanium dioxide that reflect visible light, are not helpful because the photosensitivity in this disorder results from exposure to light in the visible spectrum.
Answer 2: Steroids are not an appropriate treatment for EP.
Answer 3: Therapeutic phlebotomy is indicated for treatment of porphyria cutanea tarda to reduce iron stores.
Answer 5: Chloroquine is indicated for the management of porphyria cutanea tarda.

ILLUSTRATIONS: