A 40-year-old woman of Iranian heritage presents to a dermatologist with a persistent, scaly, pruritic rash on her feet that she has had for many years. 

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<p>A 40-year-old woman of Iranian heritage presents to a dermatologist with a persistent, scaly, pruritic rash on her feet that she has had for many years. There is no rash elsewhere on her body. </p><p>She has previously been diagnosed with palmoplantar psoriasis and prescribed topical steroid creams, including betamethasone and oral prednisone. She also received ultraviolet light treatment. There was no improvement with any of these treatments. </p><p>She has no known allergies. Her cousin, sister and uncle have psoriasis. She lives at home with her husband and children and has a pet dog.</p><p>On examination, there is a well-demarcated erythematous rash on both, more marked on the left foot. This is associated with a yellowed, dysmorphic right toenail.</p>

Professor Dedee Murrell is head of dermatology at St George Hospital, Sydney, and conjoint professor at UNSW Sydney.