A 35‐year‐old woman has noted an unusual red rash over her knuckles on her hands and perhaps to a lesser extent on her upper chest and upper back. She is otherwise healthy and has no significant medical or family history. She is on no medications. Her GP reassures her that the rash is of no significance. Over the next few months, she notices that she has much less energy than previously and is concerned that the rash may be spreading to her face. She seems to be puffy around the eyes and everyone seems to comment on it. Her GP agrees and refers her to a dermatologist for a further opinion. The dermatologist is alarmed at the extent of her rash and orders some urgent blood tests. She is started on high‐dose prednisolone to clear the rash and the dermatologist explains that she has dermatomyositis.

The rash fades successfully with steroids, but the patient notices after 3 or 4 weeks that she is having difficulty lifting her arms above her head or rising from a chair. She returns to her GP who suggests that she must stop the steroids immediately and performs some urgent blood tests.