26
Epidermolysis Bullosa
• Inherited EB is traditionally divided into three major categories – EB simplex (EBS), junctional EB (JEB), and dystrophic EB (DEB) – that differ in the ultrastructural site of blister formation (Fig. 26.1).
Fig. 26.1 Ultrastructural sites of blister formation in major forms of epidermolysis bullosa (EB). A In intact skin, the ultrastructural regions of the epidermal basement membrane zone consist of (1) basal keratinocytes and the hemidesmosomal plaque; (2) the lamina lucida; (3) the lamina densa; (4) the upper papillary dermis. B In EB simplex (EBS), blisters arise within the lower portion of basal keratinocytes. C In junctional EB (JEB), blisters form within the lamina lucida. D In dystrophic EB (DEB), blisters develop below the lamina densa. Anchoring fibrils are reduced in number in dominant DEB (DDEB) and absent or rudimentary in recessive DEB (RDEB). K5 and K14, keratin 5 and keratin 14, respectively.
• The major subtypes of EB and Kindler syndrome (now classified as a fourth form of EB) are summarized in Table 26.1.
Table 26.1
Epidermolysis bullosa (EB) subtypes.
Former names are in parentheses. Suprabasal forms of EB simplex due to desmosomal defects (e.g. plakophilin deficiency) are also included in the EB spectrum; these rare disorders feature blistering (with acantholysis in skin biopsy specimens), PPK, nail dystrophy, and hypotrichosis.
* Most severe subtype in EBS, JEB, and DEB groups, respectively.
** Dental enamel hypoplasia occurs in all forms of JEB.
† ‘EB nevi’ occasionally occur in other EB subtypes, and patients with RDEB–severe generalized have an increased risk of melanoma.
‡ Mediates anchorage between the actin cytoskeleton and the extracellular matrix via focal adhesions.
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