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Snapshot diagnosis - why has this man developed pustules on his legs?

These pustules appeared after a course of prednisolone. Is it an infection? Dr Mike Wyndham describes the case

These pustules appeared after a course of prednisolone. Is it an infection? Dr Mike Wyndham describes the case

The patient

This 63-year-old man had been a longstanding sufferer of asthma. His latest attack had been precipitated by a URTI which had not responded well to his usual inhalers. As a result, I had started him on a one-week course of prednisolone to good effect. His past medical history included maturity onset diabetes and psoriasis, which only mildly affected the extensor surfaces of his elbow and knees.

About a week after completing the course of steroids, the patient returned with a ‘good news, bad news' story. The good news was that the asthma was much better. The bad news was that he had developed a rather extensive rash over much of his arms and legs. The appearance was pustular on a red background. He was not unwell.

First instinct

The presence of pustules in a diabetic who had just had a course of steroids suggested that this was infection with Staphylococcus aureus and so I prescribed a course of flucloxacillin.

Differential diagnosis

• Milaria

• Generalised pustular psoriasis

Likely diagnosis

Although I had prescribed antibiotics, the thought in the back of my mind was that this rash was too extensive for infection. Milaria was unlikely as it

was the middle of winter and he had done little exercise to get really hot. Generalised pustular psoriasis seemed unlikely as the patient was not systemically unwell.

The hidden clue

In this case, the clue was inside the pustules. They were sterile and when the patient returned for review, the appearance of the rash was as shown. No longer were there any pustules, but erythematous skin that was peeling in places. It was now clear that this was a subacute variety of generalised pustular psoriasis where the patient does not become systemically unwell. Pleasingly, this responded well to topical treatment.

Dr Mike Wyndham is a GP in Edgware

Pustular psoriasis

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