There are many types of epidermolysis bullosa: the five main ones are listed in Table 9.2. All are charac-terized by an inherited tendency to develop blisters after minimal trauma, although at different levels in the skin (Fig. 9.12). The more severe types have a catastrophic impact on the lives of sufferers. Acquired epidermolysis bullosa is not inherited and was discussed earlier.
Several subtypes are recognized, of which the most common are the Weber–Cockayne (mainly affecting the hands and feet) and the Dowling–Meara (featur-ing herpetiform blisters on the trunk) types. Most are inherited as autosomal dominant conditions and are caused by abnormalities in genes responsible for pro-duction of the paired keratins (K5 and K14) expressed in basal keratinocytes (see Fig. 2.4). Linkage studies show that the genetic defects responsible for the most common types of simple epidermolysis bullosa lie on chromosomes 17 and 12.
Blisters form within or just above the basal cell layers of the epidermis and so tend to heal without scarring. Nails and mucosae are not involved. The problems are made worse by sweating and ill-fitting shoes. Blistering can be minimized by avoiding trauma, wearing soft well-fitting shoes and using foot powder. Large blisters should be pricked with a sterile needle and dressed. Their roofs should not be removed. Local antibiotics may be needed.
The abnormalities in the basal lamina include loss of anchoring filaments and defective laminins (; see Fig. 2.9). This rare and often lethal condition is evident at birth. The newborn child has large raw areas and flaccid blisters, which are slow to heal (Fig. 9.13). The peri-oral and peri-anal skin is usually involved, as are the nails and oral mucous membrane. There is no effective systemic treatment. Hopes for the future include adding the normal gene to epidermal stem cells, and then layering these onto the denuded skin.
There are many subtypes, all of which probably result from abnormalities of collagen VII, the major struc-tural component of anchoring fibrils
In this type blisters appear in late infancy. They are most common on friction sites (e.g. the knees, elbows and fingers), healing with scarring and milia formation. The nails may be deformed or even lost. The mouth is not affected. The only treatment is to avoid trauma and to dress the blistered areas.
In this tragic form of epidermolysis bullosa, blisters start in infancy. They are subepidermal and may be filled with blood. They heal with scarring, which can be so severe that the nails are lost and webs form between the digits (Fig. 9.14). The hands and feet may become useless balls, having lost all fingers and toes. The teeth, mouth and upper part of the oesophagus are all affected; oesophageal strictures may form. Squamous cell carcinomas of the skin are a late complication. Treatment is unsatisfactory. Phenytoin, which reduces the raised dermal collagenase levels found in this variant, and systemic steroids are disappointing. It is especially important to minimize trauma, to prevent contractures and web formation between the digits, and to combat anaemia and secondary infection. Referral to centres with expertise in management of these patients is strongly recommended.
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