Harrison's Internal Medicine Chapter 55. Immunologically Mediated Skin Diseases
Immunologically Mediated Skin Diseases: Introduction
A number of immunologically mediated skin diseases and immunologically mediated systemic disorders with cutaneous manifestations are now recognized as distinct entities with consistent clinical, histologic, and immunopathologic findings. Many of these disorders are due to autoimmune mechanisms.
Pemphigus Vulgaris Pemphigus refers to a group of autoantibody-mediated intraepidermal blistering diseases characterized by loss of cohesion between epidermal cells (a process termed acantholysis). Manual pressure to the skin of these patients may elicit the separation of the epidermis (Nikolsky's sign). This finding, while characteristic of pemphigus, is not specific to this group of disorders and is also seen in toxic epidermal necrolysis, Stevens-Johnson syndrome, and a few other skin diseases.
Pemphigus Foliaceus Pemphigus foliaceus (PF) is distinguished from PV by several features. In PF, acantholytic blisters are located high within the epidermis, usually just beneath the stratum corneum. Hence PF is a more superficial blistering disease than PV. The distribution of lesions in the two disorders is much the same, except that in PF mucous membranes are almost always spared. Patients with PF rarely demonstrate intact blisters but rather exhibit shallow erosions associated with erythema, scale, and crust formation.
Bullous Pemphigoid Bullous pemphigoid (BP) is a polymorphic autoimmune subepidermal blistering disease usually seen in the elderly. Initial lesions may consist of urticarial plaques; most patients eventually display tense blisters on either normalappearing or erythematous skin (Fig. 55-2). The lesions are usually distributed over the lower abdomen, groin, and flexor surface of the extremities; oral mucosal lesions are found in some patients. Pruritus may be nonexistent or severe.
Pemphigoid Gestationis Pemphigoid gestationis (PG), also known as herpes gestationis, is a rare, nonviral, subepidermal blistering disease of pregnancy and the puerperium. PG may begin during any trimester of pregnancy or present shortly after delivery. Lesions are usually distributed over the abdomen, trunk, and extremities; mucous membrane lesions are rare. Skin lesions in these patients may be quite polymorphic and consist of erythematous urticarial papules and plaques, vesiculopapules, and/or frank bullae. Lesions are almost always very pruritic.
Linear IgA Disease Linear IgA disease, once considered a variant form of dermatitis herpetiformis, is actually a separate and distinct entity. Clinically, these patients may resemble individuals with DH, BP, or other subepidermal blistering diseases. Lesions typically consist of papulovesicles, bullae, and/or urticarial plaques predominantly on central or flexural sites. Oral mucosal involvement occurs in some patients. Severe pruritus resembles that seen in patients with DH.
Dermatomyositis The cutaneous manifestations of dermatomyositis (Chap. 383) are often distinctive but at times may resemble those of systemic lupus erythematosus (SLE) (Chap. 313), scleroderma (Chap. 316), or other overlapping connective tissue diseases (Chap. 316). The extent and severity of cutaneous disease may or may not correlate with the extent and severity of the myositis.
Discoid lupus erythematosus.
Violaceous, hyperpigmented, atrophic plaques, often with evidence of follicular plugging, which may result in scarring, are characteristic of discoid lupus erythematosus (also called chronic cutaneous lupus erythematosus).
Scleroderma and Morphea
The skin changes of scleroderma (Chap. 316) usually begin on the hands, feet, and face, with episodes of recurrent nonpitting edema.
Scleroderma often eventuates in development of an expressionless, masklike facies.
Morphea is characterized by localized thickening and sclerosis of skin, usually affecting young adults or children. Morphea begins as erythematous or flesh-colored plaques that become sclerotic, develop central hypopigmentation, and demonstrate an erythematous border. In most cases, patients have one or a few lesions, and the disease is termed localized morphea. In some patients, widespread cutaneous lesions may occur, without systemic involvement. This form is called generalized morphea.
For two main reasons, dermatology is one of the later medical disciplines to use imaging techniques: skin lesions are readily visible to the naked eye or through a magnifying glass, allowing clinical diagnosis with no invasive examination; skin lesions can easily be biopsied or removed for histological study. This approach has therefore remained the basis of clinicopathological diagnosis of skin diseases for a long time. There has also been a third factor.
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It has long been noted anecdotally that affect, psychological
state and neurologic state have influences on
inflammatory skin diseases. Disorders such as psoriasis,
atopic dermatitis, acne and rosacea, among many
others, are reported to become exacerbated by stress.
Furthermore, it is widely believed that stress alters
cutaneous immunity. However, mechanisms responsible
for these effects have remained incompletely
understood. Scientific evidence for an influence of
the nervous system on immune and inflammatory
processes in the skin has been developed only relatively
A–D. The distribution of some common dermatologic diseases and lesions
Psoriasis. This papulosquamous skin disease is characterized by small and large erythematous papules and plaques with overlying adherent silvery scale.
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A number of immunologically mediated skin diseases and immunologically mediated systemic disorders with cutaneous manifestations are now recognized as distinct entities with consistent clinical, histologic, and immunopathologic findings. Many of these disorders are due to autoimmune mechanisms. Clinically, they are characterized by morbidity (pain, pruritus, disfigurement) and in some instances by mortality (largely due to loss of epidermal barrier function and/or secondary infection).
The skin plays an important role in maintaining the integrity of the living organism
while allowing the interaction of the organism with its environment. To fulfill these
functions, mechanical stability is as important as flexibility. The mechanical properties
of skin are very diverse depending on the anatomical location, and they evolve
throughout life from the fetus to old age. Both genetic and acquired skin diseases
modify skin biomechanics, as do intrinsic and photoaging.
Lupus Erythematosus The cutaneous manifestations of lupus erythematosus (LE) (Chap. 313) can be divided into acute, subacute, and chronic types. Acute cutaneous LE is characterized by erythema of the nose and malar eminences in a "butterfly" distribution (Fig. 55-5). The erythema is often sudden in onset, accompanied by edema and fine scale, and correlated with systemic involvement. Patients may have widespread involvement of the face as well as erythema and scaling of the extensor surfaces of the extremities and upper chest.
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