Page 392 - Medicine and Surgery

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388 Chapter 9: Dermatology and soft tissues

psoriasis, psoriatic lesions occur at sites of trauma a thin or absent granular layer. Dilated capillaries are
and damage (the K¨ oebner phenomenon) and certain seen in the oedematous papillary dermis.
drugs may exacerbate psoriasis (β blockers, lithium,
antimalarials). Management
Psoriasis is a chronic disorder that is managed rather
Pathophysiology than cured. Treatments are chosen on the basis of dis-
The epidermis is thickened with increased epidermal ease pattern and severity, patient preference and clinical
stem cells and keratinocytes. There is increased cellular response.
DNA synthesis, shortened cell cycle and rapid epidermal Emollients both topical and in the bath help reduce
turnover (turnover time is reduced from 28 to 4 days). the scaling and dryness.
Keratolytic agents (e.g. coal tar) are used both in the

Clinical features form of topical applications and shampoos to remove
Psoriasis varies in severity. Typical lesions are clearly de- the scales before applying other treatments.
marcated erythematous patches 1–10 cm in diameter. Topical corticosteroids are often used; however, there
There is a thick silvery scale, which when lifted off char- is a risk of rebound psoriasis on stopping treatment.
acteristically reveals small areas of punctate bleeding. Calcipotriol, a vitamin D analogue, is increasingly
Different distribution patterns are recognised. used either as single therapy or in combination with
Plaque psoriasis is the most common form. It usu-
topical steroids.
ally affects extensor surfaces especially the elbows and Phototherapy with ultraviolet B (UVB), or with UVA
knees, scalp and hair margin or sacrum. light and an oral psoralen (PUVA), is used in patients
Guttate (drop-like) psoriasis is an acute onset of mul-
with extensive refractory disease. These treatments are
tiple small psoriatic lesions on the trunk often in a expensive and increase the risk of skin cancer. An al-
child or young adult with no previous history of pso- ternative may be the use of a high-energy laser that
riasis. It often follows a streptococcal pharyngitis. It is treats only the affected skin.
usually self-limiting. Systemic therapy is used in life-threatening or refrac-
Pustular psoriasis is the most severe form and can
torypsoriasisincludingmethotrexate,ciclosporinand
be life-threatening. There is acute onset of diffuse retinoids all of which have systemic toxicity requiring
erythema and scaling with sheets of superficial non- monitoring.
infected pustules. If the entire skin is affected, it is
termed erythrodermic (the von Zumbusch variant). Prognosis
This may be associated with systemic upset (malaise, Psoriasis is a lifelong disease with variability in severity
fever, diarrhoea) and is potentially life-threatening. over time.
Localised forms of pustular psoriasis also occur, such
as palmoplantar pustulosis. Pityriases
Flexural or inverse psoriasis affects the inguinal re-

gion, axillae and submammary areas. There may not Pityriasis rosea
be scales visible due to moisture, the plaques therefore
appear erythematous and smooth. Definition
Pityron is Greek word for bran. The pityriases are skin
Nail involvement includes pitting, ridging and ony-

diseases characterised by fine, bran-like scales. Pityriasis
cholysis. Nail involvement is specifically associated
rosea is an acute, self-limiting condition with scaly oval
with psoriatic arthropathy.
papules and plaques mainly occurring on the trunk.
Psoriatic arthritis occurs in 5% of patients (see page

363).
Aetiology
Microscopy The cause is unknown, human herpes virus 7 has been
There is infiltration of the strium corneum with neu- suggested; however, the virus is not always detectable in
trophils, epidermal hyperplasia with hyperkeratosis and patients with pityriasis rosea.