GEMMA is a 34-year-old policy consultant who presents with a gradually expanding itchy rash on her left leg.

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<p>GEMMA is a 34-year-old policy consultant who presents with a gradually expanding itchy rash on her left leg.</p><p>This has been slowly progressing and expanding since her mid-teens, when she first noticed some small patches on the back of her calf and knee.</p><p>She has trialled topical corticosteroids and antifungals on and off, with no benefit.</p><p>Gemma is otherwise well, with no medical or family history of note. She takes no regular medications and has no known allergies.</p><p>On examination, there are extensive well-defined erythematous plaques with raised edges and overlying scale in a linear distribution extending from the buttock to heel of her left leg (pictured).</p><p>Skin and systemic examinations are otherwise unremarkable. Bacterial swabs and fungal scrapings are negative.</p><p>Skin biopsies reveal a cornoid lamella in the stratum corneum and dyskeratotic cells in the spinous layer.</p>

Dr Kate Kelso is a GP and medical editor at Australian Doctor.