Epidermolysis bullosa

Definition

Epidermolysis bullosa is a group of rare inherited skin diseases marked by the development of blisters following minimal disturbance to the skin. Blistering often appears in infancy in response to simply being held or handled; in rarer forms of the disorder, EB can be life-threatening. There is no cure for the disorder. Treatment focuses on preventing and treating wounds and infection.

Description

There are three major forms of epidermolysis bullosa (EB) and at least 16 subtypes of the disorder. The three major subtypes are EB simplex, junctional EB, and dystrophic EB and can range in severity from mildly annoying blistering to more disfiguring and life-threatening disease. Physicians decide which form of the disease is present based on which part of the epidermis (the skin's outermost layer) separates from the deeper dermis layer to form a blister. Exactly how many people have EB is unknown, but estimates place the incidence from 1 in 50,000 people to 1 in 100,000 people. Prenatal testing for families at risk of giving birth to children affected with EB has recently become available.

Causes & symptoms

EB can be inherited as the result of a dominant genetic defect (only one parent carries the defect) or a recessive genetic defect (both parents must carry the genetic defect). EB simplex results from mutations in genes responsible for keratin 5 and 14, which are proteins that give the cells of the epidermis its structure. Dystrophic EB is caused by mutations in genes for type VII collagen, the protein contained in the fibers anchoring the epidermis to the deeper layers of the skin. The specific genetic mutations in junctional EB have not been fully explained.

EB simplex is the least serious form of the disease. In most patients, the blisters are mild and do not scar after they heal. Some forms of EB simplex affect just the hands and feet; other forms of EB simplex can lead to more widespread blistering, as well as hair loss and missing teeth. Recurrent blistering is annoying but not life threatening. The second form of EB, junctional EB, does not lead to scarring. However, skin on the areas prone to blistering, such as the elbows and knees, often shrinks. In one variation of junctional EB, called gravis junctional EB of Herlitz, the blistering can be so severe that affected infants may not survive due to massive infection and dehydration. The third form of EB, dystrophic EB, varies greatly in terms of severity, but more typically affects the arms and legs. In one variation, called Hallopeau-Siemens EB, repeated blistering and scarring of the hands and feet causes the fingers and toes to fuse, leaving them mitten-like and dysfunctional.

Diagnosis

Researchers distinguish between the three major subtypes of the disease based on which layer of the epidermis separates from the deeper dermis layer of the skin below. Patients suspected of having EB should have a fresh blister biopsied for review. This is examined under an electron microscope or under a conventional microscope using a technique called immunofluorescence, which helps map the underlying structure.

Knowing that a family member has EB can help establish the diagnosis, but it is possible that parents or siblings will show no sign of the disease, either because it is caused by a new genetic mutation, or because the parents are carriers of the recessive defect but do not display the disease.

Treatment

The most important treatment for EB is daily wound care. Because the skin is very fragile, care must be taken to make certain that dressing changes do not cause further damage to the skin. Tape should not be applied directly to the skin and bandages should be soaked off if they adhere to the skin below. Infection is a major concern, so a topical antibiotic, such as mupirocin, bacitracin, or sulfadiazine, needs to be applied routinely. In patients with the recessive dystrophic EB, the anticonvulsant phenytoin is sometimes effective because it decreases production of an enzyme that breaks down collagen.

Prognosis

The prognosis of EB varies depending on the subtype of the disease. Individuals with EB simplex can live long, fulfilling lives. The severity of the junctional and dystrophic forms of EB can vary greatly. Infants affected with some forms of the disease often do not survive infancy; other forms can lead to severe scarring and disfigurement.

Prevention

Genetic testing and family planning is the only means of preventing EB. Until recently, the only option available to parents who suspected an unborn fetus could be affected with EB was to have a sample of fetal skin removed and examined at 18-20 weeks of pregnancy. Recently, investigators have outlined genetic defects associated with some variations of the disorder, making prenatal diagnosis of EB possible by taking a sample of the chorion (a part of the placenta) at about 8-10 weeks.

Key Terms

Collagen

A fibrous protein that is a component in the skin, bone, cartilage, and other connective tissue.

Dermis

The layer of skin beneath the epidermis.

Epidermis

The outermost layer of the skin.

Keratin

A protein that is the primary component of the epidermis, hair, and nails.

Further Reading

For Your Information

Books

• Olbricht, Susan M., et al. Manual of Clinical Problems in Dermatology. Boston, Mass.: Little, Brown and Company,1992.
• Sams, W. Mitchell Sams, Jr., and Peter J. Lynch. Principles and Practice of Dermatology. New York: Churchill Livingstone, 1996.

  Periodicals

• Brust, Mary D., and Andrew N. Lin. "Epidermolysis Bullosa: Practical Management and Clinical Update." Dermatology Nursing 8 (April 1996): 81-89.
• Lin, Andrew N. Lin. "Management of Patients with Epidermolysis Bullosa." Dermatologic Clinics 14 (April 1996): 381-387.

  Organizations

• American Academy of Dermatology. 930 N. Meacham Road, PO Box 4014, Schaumburg, IL 60168-4014. (847) 330-0230. http://www.aad.org.
• Dystrophic Epidermolysis Bullosa Research Association. 40 Rector Street, 8th Floor, New York, NY 10006. (212) 513-4099. http://www.debra.org.

Gale Encyclopedia of Medicine. Gale Research, 1999.