Acute monoarthritis: gout or septic arthritis?
The case
A 62-year-old man presents to the emergency department with a 24-hour history of rapidly progressive, intensely painful swelling of the right first metatarsophalangeal joint. He has type 2 diabetes (HbA1c 8.2%), hypertension treated with hydrochlorothiazide, and ischaemic heart disease. He is febrile at 38.2°C with a heart rate of 102/min; the joint is red, extremely tender and has limited movement. White cell count is 14.0 × 10^9/L (4.0–11.0), CRP 120 mg/L (below 5) and serum urate 0.48 mmol/L (0.18–0.42). Plain X-ray shows soft tissue swelling only. You are concerned about both gout and septic arthritis. What is the most appropriate next step?
Options
- AAspirate the joint before giving antibiotics
- BOral diclofenac and colchicine now, review in 48 hours
- CStart allopurinol to lower serum urate
- DCheck inflammatory markers and urate, then wait
- EIntravenous flucloxacillin and gentamicin now
Think it through before you read on. Which single option is best, and why are the other four wrong?
Show the answer and explanation
Answer
A. Aspirate the joint before giving antibiotics
Why this is the right answer
An acutely hot, swollen single joint in a febrile patient is septic arthritis until proven otherwise. Gout is more common at the first metatarsophalangeal joint, and this man has risk factors for gout (thiazide, raised urate). But gout and infection can look identical, and they can coexist. Fever, tachycardia, high white cell count and a CRP of 120 all raise concern for infection, and his diabetes increases that risk.
The only way to separate them is to examine the synovial fluid. Joint aspiration gives fluid for Gram stain, culture, cell count and polarised light microscopy for crystals. Negatively birefringent needle-shaped crystals confirm gout; organisms or a very high neutrophil count point to infection.
The sample must be taken before antibiotics are given, because even one dose can make the culture negative and leave the diagnosis uncertain for the rest of the admission. Therapeutic Guidelines (Rheumatology) and the Australian Rheumatology Association both emphasise aspiration before treatment [VERIFY].
If the patient is septic or unstable, blood cultures and joint aspiration are done quickly and antibiotics follow immediately. In a stable patient, aspiration is done first and treatment is directed by the result.
Serum urate does not settle the question. It can be normal during an acute gout attack and raised in a patient with septic arthritis.
Why the other options are wrong
- B
Anti-inflammatory treatment without excluding infection may mask a septic joint for 48 hours.
- C
Allopurinol is not started during an acute attack and does nothing for possible infection.
- D
Urate and CRP cannot distinguish gout from infection; waiting delays a time-critical diagnosis.
- E
Antibiotics before aspiration sterilise the culture; in a stable patient, aspirate first.
High-yield takeaway
A hot joint with fever is septic until proven otherwise: aspirate for Gram stain, culture and crystals before any antibiotic.
Reference: Therapeutic Guidelines: Rheumatology, Septic arthritis and Gout (2023)
Common questions
Can serum urate distinguish gout from septic arthritis?
No. Urate can be normal during an acute gout attack and raised in a patient whose joint is infected.
What if the patient is septic and unstable?
Take blood cultures and aspirate the joint quickly, then start antibiotics without waiting for results. Aspiration should still come before the first dose where possible.
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