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What's causing the rash on this woman's feet?

Dr Mike Wyndham describes a case where a middle-aged woman presented with a thick rash on both soles

 

The patient

This 52-year-old black woman works in a local dental surgery. She often finds herself getting hot, attributing it to ‘her time of life'.

She likes to wear sandals most days as it helps to keep her cool, but this is becoming an increasing problem as she has been developing a rash on both feet.

It's not particularly itchy but is covering quite a large area of the soles. Some of the rash appears quite thick. She has not noticed any blisters.

First instinct

The rash was fairly symmetrical on both feet. Could it be fungal as so many rashes often are in this region? Well, with the rash affecting both feet and also spreading on the top and away from the toe webs, fungus seemed less likely.

Differential diagnosis

• Tinea pedis

• Psoriasis

• Eczema

• Lichen planus

Fungal infection when affecting the feet commonly will be found near the toe webs – second, third and fourth. Sometimes, it may manifest as a scaling rash when it extends further on to the foot. But tinea pedis commonly affects the feet unilaterally, which was quite different from this rash.

Psoriasis may present in three ways on the foot:

• Hyperkeratosis in weight-bearing areas

• Pustular form with pustules at different stages

• Plaque accompanied by scale.

There was certainly hyperkeratosis present.

Eczema certainly occurs on the feet and a symmetrical distribution on the soles is strongly suggestive of contact. This may relate to rubber in shoes or dye in socks. Pompholyx eczema manifests as small vesicles all at about the same stage of their development.

Lichen planus on the soles of the feet tends to manifest as larger areas of dermatitis with hyperkeratosis rather than the typical small lesions. This diagnosis was a definite possibility.

It's also important to bear in mind the possibility of a drug adverse event. Bendroflumethazide is definitely capable of a lichenoid eruption. Large plaques tend to form, sometimes with scale present.

Getting on the right track

The patient had initially directed my attention to the soles of her feet, which distracted me from looking at the dorsum. The side view showed

a ‘constellation' of skin morphologies with the hyperkeratosis on the side of the sole, what appeared to be a plaque on the proximal foot and a group of small lesions on the distal foot.

The latter resembled lichen planus and a quick look in her mouth showed the classic patches on both buccal mucosae. Changing her anti-hypertensive treatment made no difference to the speed of resolution of the rash.

Dr Mike Wyndham is a GP in Edgware, north London

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