Page 868 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster
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854 C H A P T E R 23 Skin many months to years, although they may begin with an
A acute stage. The skin surface in some chronic inflammatory
dermatoses is roughened as a result of excessive or abnor-
mal scale formation and shedding (desquamation).
Psoriasis
Psoriasis is a common chronic inflammatory dermatosis,
affecting 1% to 2% of people residing in the United States.
Recent epidemiologic studies have shown that psoriasis is
associated with an increased risk of heart attack and
strokes, a relationship that may be related to a chronic
inflammatory state. Psoriasis is also associated in up to 10%
of patients with arthritis, which in some cases may be
severe.
B PAT H O G E N E S I S
Figure 23–2 Erythema multiforme. A, The target-like lesions consist Psoriasis is a multifactorial immunologic disease; both genetic
of a pale central blister or zone of epidermal necrosis surrounded by (e.g., human leukocyte antigen [HLA] types) and environ-
macular erythema. B, Early lesions show a collection of lymphocytes mental factors contribute to risk. It is not known if the inciting
along the dermoepidermal junction (interface dermatitis) associated with antigens are self or environmental. Sensitized populations of
scattered keratinocytes with dark shrunken nuclei and eosinophilic cyto- T cells home to the dermis, including CD4+ TH17 and TH1
plasm that are undergoing apoptosis. cells and CD8+ T cells, and accumulate in the epidermis.
These cells secrete cytokines and growth factors that induce
keratinocytes (Fig. 23–2, B). With time, discrete, confluent keratinocyte hyperproliferation, resulting in the characteristic
zones of basal epidermal necrosis appear, with concomitant lesions. Psoriatic lesions can be induced in susceptible persons
blister formation. In the rarer and more severe form of this by local trauma (Koebner phenomenon), which may
disease, toxic epidermal necrolysis, the necrosis extends induce a local inflammatory response that promotes lesion
through the full thickness of the epidermis. development. GWAS studies have linked an increased risk of
psoriasis to polymorphisms in HLA loci and genes affecting
Clinical Features antigen presentation, TNF signaling, and skin barrier
Erythema multiforme exhibits a broad range of severity. function.
The forms associated with infection (most often herpesvi-
rus) are less severe. Erythema multiforme caused by MORPHOLOGY
medications can progress to more serious life-threatening
eruptions, such as Stevens-Johnson syndrome or toxic epi- The typical lesion is a well-demarcated, pink to salmon–
dermal necrolysis. These forms can be life-threatening colored plaque covered by loosely adherent silver-
because they can cause sloughing of large portions of the white scale (Fig. 23–3, A). There is marked epidermal
epidermis, resulting in fluid loss and infections akin to thickening (acanthosis), with regular downward elongation
those seen in burn-injured patients. These severe forms of the rete ridges (Fig. 23–3, B). The pattern of this down-
most often occur as idiopathic reactions to drugs. ward growth has been likened to “test tubes in a rack.”
Increased epidermal cell turnover and lack of maturation
CHRONIC INFLAMMATORY results in loss of the stratum granulosum and exten-
DERMATOSES sive parakeratotic scale. Also seen is thinning of the
epidermal cell layer overlying the tips of dermal papillae
Chronic inflammatory dermatoses are persistent skin con- (suprapapillary plates), and dilated and tortuous blood vessels
ditions that exhibit their most characteristic features over within the papillae. These vessels bleed readily when the scale
is removed, giving rise to multiple punctate bleeding points
(Auspitz sign). Neutrophils form small aggregates within
both the spongiotic superficial epidermis and the parakera-
totic stratum corneum. Similar changes can be seen in super-
ficial fungal infections, which need to be excluded with
appropriate special stains.
Clinical Features
Psoriasis most frequently affects the skin of the elbows,
knees, scalp, lumbosacral areas, intergluteal cleft, and glans
penis. Nail changes on the fingers and toes occur in 30% of
cases. In most cases, psoriasis is limited in distribution, but
