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What is causing the swelling and deformity of this woman's feet?

Dr Keith Hopcroft explains how an easily missed clue was the key to this diagnosis

The patient

This 55-year-old woman, with a history of osteoarthritis of the small joints in the feet and occasional requests for prescriptions of co-codamol, presented to me hobbling and in obvious discomfort. Clearly, her symptoms had deteriorated.

First instinct

A look at her feet confirmed gross abnormalities of the small joints, with swelling, deformity and clawing – this looked like some type of deforming arthritis. Her hands showed similar – though milder – abnormalities.

She confirmed that these caused pain and stiffness too, with difficulties holding a knife and fork or opening jars.

But she had assumed this was just further evidence of wear and tear, and, though the changes weren't absolutely characteristic of osteoarthritis, she was probably right.

Differential diagnosis

  • Osteoarthritis
  • Other forms of arthritis, such as rheumatoid
  • Gout
  • Neurological pathology

Osteoarthritis was the front runner, not least because it is so frequently seen in primary care and certainly can deform the small joints of the hands and feet.

Less common, though always on the differential, is rheumatoid arthritis – but the pattern and appearance here wasn't typical.

Chronic tophaceous gout was another possibility – it can produce large, deforming crystal deposits around the tendons and joints of the hands and feet. But she had never been diagnosed with gout,

had never had a monarticular attack and had no family history of the condition.

Clawing of the toes can be caused by neurological disorders, but she had no other neurological symptoms and a brief neurological examination was normal.

The hidden clue

Osteoarthritis remained top of the list, though some features – especially the degree of pain and deformity – were enough to persuade me to explore further by sending off some bloods.

This revealed a normal FBC, a moderately raised C-reactive protein, a normal uric acid and a negative rheumatoid factor.

As these suggested a possible inflammatory process, I decided to examine her again, including looking at her other joints. This time, I noticed a symmetrical scaly rash on her knees – psoriasis.

Getting on the right track

Further examination revealed changes on her nails too – symmetrical and typical of psoriasis – which was another clue that I had missed.

I referred her to the local rheumatologist who confirmed that she had psoriatic arthritis.

 

Dr Keith Hopcroft is a GP in Laindon, Essex

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