The differential diagnosis of shin lesions includes the following conditions:

• erythema nodosum
• pretibial myxoedema
• pyoderma gangrenosum
• necrobiosis lipoidica diabeticorum

Below are the characteristic features:

Erythema nodosum

• symmetrical, erythematous, tender, nodules which heal without scarring
• most common causes are streptococcal infections, sarcoidosis, inflammatory bowel disease and drugs (penicillins, sulphonamides, oral contraceptive pill)

Pretibial myxoedema

• symmetrical, erythematous lesions seen in Graves' disease
• shiny, orange peel skin

Pyoderma gangrenosum

• initially small red papule
• later deep, red, necrotic ulcers with a violaceous border
• idiopathic in 50%, may also be seen in inflammatory bowel disease, connective tissue disorders and myeloproliferative disorders

Necrobiosis lipoidica diabeticorum

• shiny, painless areas of yellow/red skin typically on the shin of diabetics
• often associated with telangiectasia