1164
U N I T 1 3
Integumentary Function
Stevens-Johnson syndrome. Lateral pressure causes the
surrounding skin to separate easily from the dermis
(
Nikolsky sign
). The tracheobronchial mucosa and con-
junctiva may be involved in severe cases with resultant
scarring. Ophthalmologic consultation is required when
ocular involvement in present.
Treatment.
Treatment of erythema multiforme minor
and less-severe cases of Stevens-Johnson syndrome
includes relief of symptoms using compresses, antipru-
ritic drugs, and topical anesthetics. Corticosteroid ther-
apy may be indicated in moderate cases, although its
use is controversial. For severe cases of Stevens-Johnson
syndrome and toxic epidermal necrolysis, hospitaliza-
tion is required for fluid replacement, respiratory care,
administration of antibiotics and analgesics, and appli-
cation of moist dressings. When large areas of skin are
detached, the care is similar to that of a thermal burn.
Intravenous immunoglobulin may hasten the healing
response of the skin. Generally, healing is a slow pro-
cess, taking 6 weeks or more to regenerate skin. The
mucous membranes heal slowly and follow-up treat-
ment is often needed for ophthalmologic and mucous
membrane sequelae. Discontinuation of the responsible
drug and chemically related compounds is imperative,
as are measures to prevent future exposures to the drug.
Papulosquamous Dermatoses
Papulosquamous dermatoses are a group of skin dis-
orders characterized by scaling papules and plaques.
Among the major papulosquamous diseases are psoria-
sis, pityriasis rosea, and lichen planus.
Psoriasis
Psoriasis is a common, chronic, inflammatory skin dis-
ease characterized by raised erythematous plaques with
silvery scales.
37–40
It affects approximately 2% of the
population and occurs worldwide, although the inci-
dence is lower in warmer, sunnier climates. The aver-
age age of onset is in the third decade; its prevalence
increases with age. Approximately one third of persons
have a genetic history, indicating a hereditary factor.
Childhood onset of the disease is more strongly associ-
ated with a family history than psoriasis occurring in
adults older than 30 years of age. In rare cases, psoriasis
is associated with arthritis (see Chapter 44).
Etiology and Pathogenesis.
Although the primary
cause of psoriasis is uncertain, it is thought to be an
immunolologic disorder in persons with a genetic pre-
disposition. It is not known if the inciting antigen is of
self or environment origin. A genetic component is sup-
ported by population studies indicating a greater inci-
dence of psoriasis among relatives of persons with the
disease than among the general population. There is a
strong association between psoriasis and the human leu-
kocyte antigen-C (HLA-C), particularly the HLA-Cw6
allele.
40
Immunologically, T lymphocytes may be the
key to the pathogenesis of psoriasis.
40
Eruption of pso-
riatic lesions coincides with T-cell infiltration into the
epidermis, and resolution of the lesions follows disap-
pearance or reduction in epidermal T cells, suggesting
a T-cell–mediated release of cytokines and growth fac-
tors that stimulate abnormal growth of keratinocytes
and dermal blood vessels. Accompanying inflamma-
tory changes are caused by infiltration of neutrophils
and monocytes. Environmental stimuli may trigger the
release of cytokines and growth factors from keratino-
cytes and other cells, with ensuing immune and inflam-
matory responses that lead to the full development of
psoriatic lesions. For example, psoriatic lesions can be
induced in susceptible individuals by trauma, a process
known as the
Köbner phenomenon
.
Clinical Features.
Histologically, psoriasis is character-
ized by increased epidermal cell turnover with marked
epidermal thickening, a process called
hyperkeratosis
.
The granular layer (stratum granulosum) of the epider-
mis is thinned or absent, and neutrophils are found in
the stratum corneum. There also is an accompanying
thinning of the epidermal cell layer that overlies the
tips of the dermal papillae, and the blood vessels in the
dermal papillae become tortuous and dilated. These
capillary beds show permanent damage even when the
disease is in remission or resolved. The close proximity
of the vessels in the dermal papillae to the hyperkera-
totic scale accounts for multiple, minute bleeding points
that are seen when the scale is lifted.
Psoriasis most frequently affects the elbows, knees,
scalp, lumbosacral area, and intragluteal cleft. The
primary lesions are sharply demarcated, thick, red
plaques covered by a silvery scale that varies in size
and shape (Fig. 46-16). In darker-skinned persons, the
plaques may appear purple. There may be excoriation,
thickening, or oozing from the lesions. A differen-
tial diagnostic finding is that the plaques bleed from
minute points when removed, which is known as the
Auspitz sign
.
FIGURE 46-15.
Erythema multiforme. Characteristic targetlike
lesions are noted here. (From Goodheart HP. Goodheart’s
Photoguide to Common Skin Disorders. Philadelphia, PA:
Wolters Kluwer Health | Lippincott Williams &Wilkins;
2009:311.)
