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What is causing the itchy rash on this woman’s foot?



 

The patient

A 60-year-old lady presented with an itchy rash on the dorsum of her right foot. There was no history of local injury, eczema or allergies.

She had been aware of the rash for a couple of weeks and reported that it seemed to be ‘creeping’ up her foot.

She had an unremarkable past medical record and, in particular, no history of previous dermatological problems.

She took occasional over-the-counter co-codamol for her arthritis, but was on no prescribed medication.

First instinct

A quick glance at her foot revealed an unusual-looking skin rash extending over its dorsum. The lesion was flat to the touch and non tender. The lesion was unilateral, and a quick survey of the rest of her skin showed no other rashes. Otherwise, she looked perfectly well.

Differential diagnosis

• Fungal infection

• Eczema

• Erythema migrans

• Cutaneous larva migrans

Fungal infections are common, typically unilateral and show a predilection for the feet, so this diagnosis seemed likely. They may show an active edge, too – although this example seemed particularly florid, and it was odd that the skin within the edge seemed normal.

The severity of the itch suggested eczema, although the asymmetry and appearance were against this – unless it represented an allergic contact eczema of some sort, though there were no clues in the history to suggest this.

The extension of the lesion made me wonder about erythema migrans, the skin manifestation of Lyme disease. The only other rash I could recall that had a similarly migratory appearance was cutaneous larva migrans. But these possibilities seemed unlikely, largely because they are so rare.

The hidden clue

The diagnostic trail warmed up only when I asked about recent travel, given that Lyme disease and cutaneous larva migrans had crossed my mind. She confirmed that she had just returned from holiday in Jamaica and had spent a lot of time on the beach.

We had had two other cases of cutaneous larva migrans in the practice, so I talked to one of my colleagues about his previous experience.

Getting on the right track

Closer scrutiny – in the light of the history – confirmed the characteristic serpiginous rash of cutaneous larva migrans. She was prescribed oral mebendazole and after a few weeks, the skin eruption faded away.

Dr Rajiv Ghurye and Dr Simon Giles are GPs in Shanklin, Isle of Wight

Competing interests None declared

Patient presenting with cutaneous larva migrans Cutaneous larva migrans