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Snapshot diagnosis - why is this woman's ankle red and acutely painful?

A normally healthy 65-year-old woman has a warm, red, swollen ankle. Is it an infection, gout or an arthropathy? Dr Hercules Robinson describes how he came to the diagnosis

A normally healthy 65-year-old woman has a warm, red, swollen ankle. Is it an infection, gout or an arthropathy? Dr Hercules Robinson describes how he came to the diagnosis

The patient

A 65-year-old woman asked for a home visit. She gave a history of an acutely painful swollen ankle that had developed over three days, leaving her unable to weight bear at all on the ankle. She also felt generally unwell.

She had no past history of any note and seldom came to the surgery. She looked unwell and had a moderate fever. General examination was normal. Her ankle was grossly swollen, warm, red and exquisitely tender.

First instinct

I felt she had a septic arthritis in view of the speed of onset, moderate fever and swollen, warm, red joint.

I arranged her immediate admission to hospital.

Differential diagnosis

• Infection: non-gonococcal septic arthritis, gonococcal septic arthritis, viral, associated with bacterial endocarditis

• Post-infection: reactive arthritis, rheumatic fever

• Spondyloarthropathy: ankylosing spondylitis, psoriatic arthritis, inflammatory bowel disease

• Oligo-articular presentation: rheumatoid arthritis, SLE, inflammatory polyarthropathy

• Gout and pseudo-gout

Getting on the right track

In hospital, she was given intravenous high-dose antibiotics. An aspirate of the joint failed to detect a bacterial infection. Her fever settled and she was discharged. But she still had a swollen and very painful ankle and was unable to weight bear. There was no history of recent travel, diarrhoea or other infection.

There was no history that would suggest an STI. There were no abdominal symptoms and no shortness of breath on examination. There was also no history of attacks of pain in the halluces. General examination was normal except for the swollen joint.

Routine investigations revealed a very high ESR, high CRP, negative rheumatoid factor and negative auto-antibody screen. Her urate was negative. A plain X-ray showed marked loss of joint space and some demineralisation. A bone scan was carried out to exclude osteomyelitis.

The hidden clue

She gave a negative family history of rheumatoid arthritis, but mentioned that her sister had psoriasis. Two years before this recent episode she had polyarthropathy, which was investigated but no diagnosis was made. This fully resolved. Inspection of her nails revealed some onycholysis and a few pits. Her skin was clear.

Outcome

It was felt that she probably had an unusual presentation of psoriatic arthritis. She was started on sulfasalazine but after a four-month trial there was no improvement and her symptoms were unaltered, as were her markedly raised inflammatory markers. Meanwhile I was called to see her with acute abdominal pain.

She had signs of peritonitis. She was found to have a sigmoid perforation, presumably due to her NSAIDs.

She was eventually started on methotrexate and gradually her ankle became less painful and her need for potent analgesia reduced and then ceased. Her inflammatory markers – ESR and CRP both above 100 – returned to normal.

The diagnosis of psoriatic arthritis – albeit with an unusual presentation – remained the most likely.

Dr Hercules Robinson is a GP in Caithness

• Do you have an unusual case – with a clinical photo – that would make a good Snapshot Diagnosis? Contact clinical editor Adam Legge at alegge@cmpmedica.com or call 020 7921 8097

Why is this woman's ankle red, swollen and acutely painful?

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