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390 Chapter 9: Dermatology and soft tissues

Aetiology Sex
50% of cases have no obvious underlying cause. Aetio- F > M
logical agents include:
Herpes simplex in 33% of cases; may cause recurrent Aetiology

attacks. Streptococcal pharyngitis is the most common asso-
Mycoplasma pneumoniae. ciated condition.

Other infections, e.g. vaccinia, orf, streptococci, tu- Many cases are idiopathic but this is a diagnosis of

berculosis, histoplasmosis. exclusion.
Drugs, e.g. sulphonamides, penicillin, phenytoin, bar- Drugs: Penicillin, oral contraceptive pill.

biturates and carbamazepines. Pregnancy.
Connective tissue disorders, such as systemic lupus Conditions with hilar lymphadenopathy: Sarcoido-

erythematosus. sis, tuberculosis, coccidioidomycosis, histoplasmosis,
Hodgkin’s lymphoma and Chlamydophila pneumo-
niae.
Clinical features
Gastrointestinal disorders: Inflammatory bowel dis-
Lesions are pinkish red erythematous papules/plaques
ease, Behc¸ˆ et’s syndrome and bacterial gastroenteri-
with central clearing or concentric rings (target lesions).
tides.
Distributionisusuallysymmetricalaffectingthebacksof
limbs, hands and feet. Disseminated rash with mucosal
Clinical features
involvement with conjunctivitis and necrotic mucosal
Painfulbluish-rednodulesupto5cmindiameterappear
ulcers is termed Stevens–Johnson syndrome. This is of-
in crops over 2 weeks on the anterior surface of both
ten associated with systemic symptoms.
lowerlegs.Theyslowlyfadeleavingbruisingandscarring
of skin. Malaise, fever and arthralgia may accompany the
Management
rash.
The withdrawal of any causative drug and treatment of
any associated infection is essential. Short courses of Management
oral steroids are sometimes used but their efficacy and Symptomatic treatment and management of any under-
safetyareunclear.Patientswithrecurrenterythemamul- lying cause is essential. Recovery may take weeks, and
tiforme resulting from herpes simplex can be prevented there may be recurrence.
with prophylactic aciclovir.
Urticaria
Prognosis
Disease is usually self-limiting clearing in 2–3 weeks but Definition
death can occur with Stevens–Johnson syndrome. Urticaria is an itchy erythematous eruption ranging
from nettle rash to large weals/plaques with palpable
skin oedema. Most cases of urticaria are acute and self-
Erythema nodosum limiting within a few hours, occasionally with recurrent
episodes for up to 6 weeks. Acute urticaria often has an
Definition
identifiable trigger. Chronic urticaria lasts from 6 weeks
Erythema nodosum is an immune-mediated disorder
and up to 10 years. There is often no identifiable trigger
resulting in red tender pretibial subcutaneous nodules.
in chronic urticaria.
Incidence Prevalence
1–5 per 100,000 per year. Affects up to 25% of the population.

Age Age
Peak incidence 15–40 years. Most common in children and young adults.