Susceptibility to atopic dermatitis is often inherited; the disorder is concordant in 80% of identical twins and 20% of fraternal twins. It usually appears in early childhood and remits spontaneously as patients mature into adults. Children with atopic dermatitis often have asthma and allergic rhinitis, termed the atopic triad. Recent genetic studies have identified polymorphisms associated with increased risk in genes that encode proteins involved in keratinocyte barrier function, innate immunity, and T cell function.
Erythema multiforme is characterized by epithelial injury mediated by skin-homing CD8+ cytotoxic T lymphocytes. It is an uncommon, usually self-limited disorder that appears to be a hypersensitivity response to certain infections and drugs. Antecedent infections include those caused by herpes simplex, mycoplasma, and some fungi, while implicated drugs include sulfonamides, penicillin, salicylates, hydantoins, and anti-malarials. The cytotoxic T cell attack is focused on the basal cells of cutaneous and mucosal epithelia, presumably due to recognition of still unknown antigens. Certain human lymphocyte antigen (HLA) haplotypes are associated with the disease.
Fig. 24.1 Eczematousdermatitis.(A)Patternederythemaandscalestem-mingfromanickel-inducedcontactdermatitisproducedbyanecklace.
(B)Microscopically,thereisaccumulationoffluid(spongiosis)betweenepidermalcells,whichmayprogresstofrankblisterformation.
MORPHOLOGYAffectedindividualspresentwithawidearrayoflesions,whichmayincludemacules,papules,vesicles,andbullae(hencethetermmultiforme).Well-developedlesionshaveacharacteristic“targetoid”appearance(
Fig.24.2A ).Earlylesionsshowasuperficialperivascularlymphocyticinfiltrateassociatedwithdermaledemaandmarginationoflymphocytesalongthedermoepidermaljunctioninintimateassociationwithapoptotickeratinocytes(see
Fig.24.2B ).Withtime,discrete,confluentzonesofbasalepidermalnecrosisappear,withconcomitantblisterformation.Inararerandmoresevereformofthisdisease,toxic epidermal necrolysis, thenecrosisextendsthroughthefullthicknessoftheepidermis.
http://ebooksmedicine.net
Fig. 24.2 Erythemamultiforme.(A)Targetlikelesionsconsistingofapalecentralblisterorzoneofepidermalnecrosissurroundedbymacularery-thema.(B)Earlylesionsshowlymphocytesalongthedermoepidermaljunc-tion(interfacedermatitis)associatedwithscatteredapoptotickeratinocytes,markedbydarkshrunkennucleiandeosinophiliccytoplasm.
Erythema multiforme has a broad range of severity. The forms associated with infection (most often herpesvirus) are less severe. Erythema multiforme caused by medications may progress to more serious eruptions, such as Stevens-Johnson syndrome or toxic epidermal necrolysis. These forms can be life-threatening, as they may cause sloughing of large portions of the epidermis, resulting in fluid loss and infections complications similar to those seen in burn-injured patients.
Chronic inflammatory dermatoses are persistent skin conditions that exhibit their most characteristic features over many months to years, although they may begin with an acute stage. The skin surface in some chronic inflammatory dermatoses is roughened as a result of excessive or abnormal scale formation and shedding (desquamation).