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What is causing the rash on this man's feet?

Dr Keith Hopcroft explains what prompted him to revise his initial diagnosis in this teenager with a rash on the feet

The patient

‘I think I've got trench foot.' This was an impressive opening gambit from my 17-year-old patient. He'd recently attended a music festival during which he'd endured the associated soakings and wallowings in mud. Since he'd returned, he'd noticed a rash on both feet and an unpleasant smell that was bothering his parents and girlfriend. The lesions didn't itch and weren't painful.

First instinct

Smelly feet in an adolescent are usually simply the result of poor hygiene – the effect of sweating and being encased in filthy trainers – or a fungal infection, or often both. The rash was most marked on his heels, and a cursory glance served only to reinforce this diagnosis.

Differential diagnosis

  • Poor hygiene
  • Fungal infection
  • Hyperkeratotic skin
  • Pompholyx
  • Verrucas
  • Pitted keratolysis.

Thickened skin is common on the heels, sometimes with painful cracks – but this usually occurs in much older patients.  Given the distribution and the symmetry of the rash, pompholyx was another possibility – but the appearance was far from typical and the lack of itch was surprising.

Closer scrutiny showed lesions similar to multiple verrucas, something I have seen before – though never this extensive nor symmetrical, so this seemed unlikely. Pitted keratolysis, a corynebacterium infection, was more of a possibility given the appearance and the distribution on the pressure areas. It's not a diagnosis we see often though, so I stuck with my instinct and treated him with an antifungal cream.

The hidden clue

‘The trench foot's no better, doc,' was the only clue I needed when he reappeared two weeks later. And the smell, if anything, was worse – a characteristic feature of pitted keratolyis. Now, with the aid of a magnifying glass, I was able to convince myself that the lesions comprised tiny pits.

Getting on the right track

This time I gave him a topical antibiotic – and there was no return appointment, which suggests that either he had given up on me and decided to live with the lesions and smell, or, more likely, the diagnosis of pitted keratolyis was correct.

 

Dr Keith Hopcroft is a GP in Laindon, Essex

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