The commonest reason septic arthritis is missed in a rheumatology clinic is that the patient already has a crystal diagnosis on the problem list. Gout does not protect against infection, and the two can coexist in the same joint — long-standing tophaceous disease, diabetes and immunosuppression all raise the risk of both.
The features that supposedly separate them do not, in practice. Fever occurs in gout. A raised CRP occurs in gout. Rapid onset overnight occurs in both. A serum urate taken during an acute attack can be normal or low and settles nothing either way.
If the joint is hot and the patient is systemically unwell, aspirate it and send fluid for Gram stain, culture and polarised microscopy before starting steroids. Finding crystals does not exclude sepsis; only the culture does. Where aspiration is not possible on the day, that is a reason to seek help, not a reason to treat the flare and review in a week.
- Aspirate any hot joint in a patient who is febrile or systemically unwell, whatever the existing diagnosis
- Send for Gram stain and culture as well as polarised microscopy — crystals do not exclude infection
- Do not use a normal serum urate during an attack to argue against gout, or a raised one to argue for it
- Hold intra-articular steroid until infection has been excluded
- Prosthetic joints and immunosuppressed patients warrant a lower threshold and earlier orthopaedic or ID input
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