Describe key points
|Site of blister||Characteristics||Differential diagnosis||Appearance|
|Subcorneal||Very thin roof breaks easily||Impetigo, miliaria, SSSS|
|Intra-epidermal||Thin roof ruptures to leave denuded surface||Acute eczema, varicella, herpes simplex, pemphigus|
|Subepidermal||Tense roof often remain intact||Bullous pemphigoid, dermatitis herpetiformis, erythema multiforme, TEN, friction blisters|
Epidermolysis bullosa (EB) refers to a group of inherited disorders in which there are mutations in specific keratin proteins (EB simplex), hemidesmosomes (junctional EB), anchoring filaments or type VII collagen (dystrophic EB). Minor trauma results in blisters and erosions, the split site and severity depending on the specific defect.
There are at least 9 distinct immunobullous diseases due to autoantibodies directed at differing components of the desmosome complex. Skin biopsy and direct immunofluorescence are diagnostic and there may be detectable circulating skin antibodies. A specialist dermatologist should manage these disorders as high dose corticosteroids and immunosuppressive medication may be required for control.
Bullous pemphigoid is the most common immunobullous disease and affects the elderly. It may start off as dermatitis or a non-specific pruritic rash that eventually develops subepidermal bullae.
Dermatitis herpetiformis results in intensely itchy vesicles and crusts on scalp, elbows, buttocks, knees and elsewhere. IgA autoantibodies to reticulin, gliadin and/or endomysium may be detected in serum. It is invariably associated with gluten-sensitive enteropathy although this may be asymptomatic. Dapsone rapidly controls itching and blistering but gluten-free diet is required long term for control.
Pemphigus has various subtypes caused by pathogenic IgG antibodies to intraepidermal cell adhesion molecules. Pemphigus vulgaris is potentially fatal; it usually presents with oral ulceration followed by widespread denudation.