CUTANEOUS SIGNS OF SYSTEMIC DISEASE:

Some dermatoses are associated with a variety of underlying systemic diseases. Furthermore some medical conditions may present with cutaneous features.
Erythema nodosum
Erythema nodosum has a number of underlying causes (Table 23.8). It presents as painful or tender dusky blue-red nodules, commonly over the shins or lower limbs, which fade over 2-3 weeks leaving a bruised appearance (see Fig. 23.39). It is most common in young adults, especially females. It may be associated with arthralgia, malaise and fever. The inflammation involves the dermis and the subcutaneous layer (panniculitis).
Treatment
Table 23-8. Causes of erythema nodosum
Streptococcal infection*
Drugs* (e.g. sulphonamides, oral contraceptive)
Sarcoidosis*
Idiopathic*
Yersinia infection
Fungal infection (histoplasmosis, blastomycosis)
Tuberculosis
Leprosy
Inflammatory bowel disease
Chlamydia infection

*Common causes in the UK
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Symptomatic therapy with non-steroidal anti-inflammatory drugs (avoid in pregnancy), light compression bandaging and bed rest are all that are necessary as the condition resolves spontaneously. The underlying cause should be treated. In very persistent cases dapsone (100 mg daily), colchicine (500 μg twice daily) or prednisolone (up to 30 mg daily) can be useful.
Erythema multiforme
Erythema multiforme (EM) is a hypersensitivity rash of acute onset frequently caused by infection or drugs. A cell-mediated T lymphocytic response is seen in the skin, which causes epidermal cell death.
In 50% of cases, the cause is not found but the following should be considered:
herpes simplex virus (the most common identifiable cause)
other viral infections (e.g. EBV, orf disease)
drugs (e.g. sulphonamide, anticonvulsants)
mycoplasma infection
connective tissue disease (e.g. SLE, polyarteritis nodosa)
HIV infection
Wegener's granulomatosis
carcinoma, lymphoma.
Clinically the lesions can be erythematous, polycyclic, annular or show concentric rings called 'target lesions' (Fig. 23.22). Frank blistering is not uncommon. The rash tends to be symmetrical and commonly affects the limbs, especially the hands and feet where palms and soles may be involved. Occasionally there is severe mucosal involvement leading to necrotic ulcers of the mouth and genitalia, and a conjunctivitis ('EM major' - previously called Stevens-Johnson syndrome - see Box 23.3). The term 'EM minor' may be used for cases without mucosal involvement.

Stevens-Johnson syndrome
This term is now used for a mild form of toxic epidermal necrolysis (p. 1359) which shares similar mucosal lesions to 'erythema multiforme major' but does not show typical target lesions. Both Stevens-Johnson syndrome and toxic epidermal necrolysis are more likely to be drug induced.

Erythema multiforme usually resolves in 2-4 weeks. Rarely, recurrent erythema multiforme can occur and this is triggered by herpes simplex infection in 80% of cases.
Treatment
This is symptomatic and involves treating the underlying cause. Some advocate the use of oral steroids in severe disease but this remains controversial.
Recurrent erythema multiforme can be treated with prophylactic oral aciclovir (200 mg twice daily) even if no cause has been found, as 80% appear to be driven by herpes simplex virus. In resistant cases, azathioprine (1-2 mg/kg daily) is used.