By Gary M. White, MD
Photo courtesy Gary Cole, MD
Erythropoietic protoporphyria (EPP) is a rare inherited metabolic disorder characterized in about 90% of cases by a deficiency of the enzyme ferrochelatase (FECH gene mutation). Acute photosensitivity beginning in childhood is characteristic. Patients are photosensitive to sunlight and some types of artificial light, e.g. fluorescent lights. Alternatively, the existence of cytosine at IVS3-48 in trans to a mutated FECH allele may result in a low expression of FECH and the development of the EPP phenotype.
Increased protoporphyrins are found in the blood and stool. Flourescent microscope of RBC's is the screening method of choice. AD inheritance is considered the rule, but AR inheritance does occur [BJD 1996;134;880]. Approximately 5% of patients develop liver failure (which may occur as early as adolescence) which may necessitate transplantation. Caution must be taken with surgery a the lights may induce a photo toxic reaction. Pregnancy has been shown to often lower circulatin erythrocye protoporphyrin levels, leading to decreased photosensitivity in pregnancy [JAAD 1997;36;40]. Wavelengths between 320 and 595 mm are most likely to cause a reaction.
Burning within a few minutes of sunlight exposure and erythema, edema and rarely vesiculation within hours occurs. Because the pain may last for days and is resistant to even narcotic analgesics, children quickly learn to avoid the sun. The nose, dorsa of the hands and tops of the ears are typically affected. In the chronic stages, linear scars, waxy thickening and an aged appearance occur. Systemic involvement has included hemolytic anemia, liver disease and cholelithiasis.
Ferrochelatase catalyses the insertion of iron into the protoporphyrin molecule to form heme. The ferrochelatase gene is found on chromosome 18.
Opaque physical barrier sunscreens, sun avoidance and protective clothing are recommended.
Oral cimetidine 30 to 40 mg/kg/day given BID resulted in dramatic improvement in photosensitivity within 2 weeks in 3 pediatric patients (ages 4, 10 and 13) [JAMA Derm 2016;152;1258]. Laboratory studies also showed a reduction in serum erythrocyte protoporphyrin levels and improved liver function.
NBUVB phototherapy was beneficial and well tolerated in a review of 12 patients with EPP. Home phototherapy was also found to be effective and well tolerated [BJD April 2014].
Colestipol 2 g twice daily (during summer and early autumn) has been shown to increase time to photosensitivity onset when outside and in some cases, prevent photosensitivity completely [JAAD 2014 Feb].
Afamelanotide increases melanin density, skin pigmentation and light-tolerance. A study of 115 patents showed that afamelanotide 16 mg implant exhibits good clinical effectiveness and under long-term routine conditions Br J Dermatol. 2015;172;1601. It is also used in solar urticaria.
A systematic review did not detect an efficacy of β-carotene, vitamin C or N-acetyl cysteine in well-designed studies. It has been recommended that the LFT's be followed every months and a liver biopsy done if persistent elevations are detected.
A teenage girl presented with hand and foot swelling and a photodistributed rash in areas of sun exposure after playing golf. She had milder similar eruptions over the last 2 years. No family members were affected [JAMA Derm 2016;152;937].
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