Why This Station Is High-Yield
A hot, swollen, single joint is one of the most common acute presentations in medicine, and gout is by far the most common inflammatory arthritis, yet it shares its presentation with septic arthritis, a genuine emergency that must never be missed. This overlap is exactly why acute monoarthritis appears so often in OSCEs: examiners want to see whether you can hold "must exclude septic arthritis" in mind even while gout looks like the obvious answer.
⚠️ Red Flag
The single most important rule in this station: any acute hot, swollen joint is septic arthritis until proven otherwise. Even with a classic gout history, joint aspiration to rule out infection is mandatory before committing to a diagnosis of gout alone, unless the diagnosis is already firmly established from a previous confirmed episode.
Structuring the Assessment
- 1History: onset, joint(s) involved, previous episodes, triggers, systemic symptoms (fever, rigors)
- 2Examination: look, feel, move of the affected joint, plus a septic screen (temperature, heart rate, signs of a source of infection elsewhere)
- 3Investigations: joint aspiration is the definitive investigation whenever septic arthritis cannot be confidently excluded
- 4Management: differs completely depending on the cause, so a working diagnosis must be reached quickly
Key History Points
🧠 Mnemonic
PODCAST for acute monoarthritis history:
- Previous episodes (gout classically recurs, often at the same joint)
- Onset (gout: rapid, peaking within 24 hours; septic arthritis: hours to a couple of days)
- Diet and alcohol (purine-rich food, beer, spirits precipitate gout)
- Comorbidities (renal impairment, hypertension, metabolic syndrome, psoriasis for reactive causes)
- Additional joints/systemic symptoms (fever suggests septic arthritis or a systemic inflammatory arthritis)
- Started new medications (diuretics, especially thiazides, precipitate gout)
- Trauma or recent joint procedure (portal of entry for septic arthritis, e.g. recent joint injection)
💎 Clinical Pearl
Classic gout presentation: first metatarsophalangeal joint ("podagra"), waking the patient from sleep with severe pain reaching maximum intensity within 12–24 hours, often precipitated by alcohol, a purine-rich meal (red meat, seafood), dehydration, or starting/stopping medications that affect urate levels.
Examination Findings
- Look: erythema, swelling, tophi (chalky white urate deposits, classically on the pinna of the ear, finger pads, or around joints in chronic tophaceous gout)
- Feel: warmth, effusion, exquisite tenderness, sometimes overlying skin desquamation in severe acute gout
- Move: markedly restricted range of movement due to pain, both active and passive
⚠️ Red Flag
Never force passive movement of a suspected septic joint, and note that inability to bear weight or any active movement at all is a red flag for septic arthritis over gout, though there is significant overlap and this alone cannot reliably distinguish them.
Differentiating the Big Three, Joint Aspiration Is Key
| Feature | Gout | Pseudogout (CPPD) | Septic arthritis |
|---|---|---|---|
| Crystal | Monosodium urate | Calcium pyrophosphate | None (organisms seen/cultured) |
| Crystal shape/birefringence | Needle-shaped, negatively birefringent | Rhomboid-shaped, positively (weakly) birefringent | N/A |
| Typical joint | 1st MTP, ankle, knee | Knee (most common), wrist | Any, commonly knee, hip |
| Onset | Rapid (peaks 12-24h) | Rapid, similar to gout | Hours to days |
| Fever | Can occur but usually mild | Can occur | Common, often high-grade |
| Fluid appearance | Cloudy/turbid | Cloudy/turbid | Frankly purulent |
| X-ray | Normal (chronic: erosions with overhanging edge) | Chondrocalcinosis (linear calcification in cartilage) | Usually normal acutely |
💎 Clinical Pearl
Mnemonic for crystal birefringence: "Urate is Ugly and Negative" (needle-shaped, negatively birefringent), "Pyrophosphate is Positive" (rhomboid, positively birefringent). Getting this the wrong way round is one of the most common exam errors.
Joint Aspiration, Send For
- Microscopy: cell count, crystal analysis under polarised light
- Culture and sensitivity: mandatory whenever septic arthritis is a possibility
- Gram stain
⚠️ Red Flag
Never delay antibiotics for suspected septic arthritis while waiting for aspiration results if the patient is systemically unwell. Aspirate first if it can be done rapidly, but empirical IV antibiotics should not be significantly delayed, following local sepsis protocols, treatment is time-critical.
Acute Gout Management
First-line options (choice depends on comorbidities):
- NSAIDs (e.g. naproxen), with a proton pump inhibitor for gastroprotection; avoid in renal impairment, heart failure, or active peptic ulcer disease
- Colchicine, useful when NSAIDs are contraindicated (e.g. renal impairment, on anticoagulation); causes diarrhoea at higher doses, dose-reduce in renal impairment
- Oral or intra-articular corticosteroids, useful when NSAIDs and colchicine are both contraindicated or poorly tolerated
💎 Clinical Pearl
Never start allopurinol during an acute gout flare. Starting urate-lowering therapy acutely can paradoxically worsen or prolong the attack by causing further crystal shedding from tissue deposits as urate levels fall rapidly. Allopurinol is started only after the acute attack has fully settled, typically after 2-4 weeks, and if already established on allopurinol at the time of a flare, it should generally be continued rather than stopped.
Long-Term Urate-Lowering Therapy
- Indications to start: two or more attacks per year, tophi, urate nephropathy/renal stones, or a first attack in someone with significant comorbidity (CKD, diuretic use)
- First-line: allopurinol, started low and titrated against serum urate level (target typically <300 µmol/L, or <360 µmol/L in less severe disease), with cover (NSAID or colchicine) for the first 3-6 months to prevent a treatment-precipitated flare
- Second-line: febuxostat, if allopurinol not tolerated or contraindicated
Lifestyle Advice
- Reduce alcohol, particularly beer and spirits
- Reduce purine-rich foods (red meat, offal, shellfish)
- Weight loss if overweight (gradual, as rapid weight loss can itself precipitate a flare)
- Adequate hydration
- Review medications that raise urate (thiazide diuretics, aspirin at low doses)
Red Flags, Never Miss
⚠️ Red Flag
- Fever, systemic upset, or a single very hot joint with severe pain out of proportion to a typical gout flare, treat as septic arthritis until excluded
- Polyarticular presentation with systemic symptoms, consider reactive arthritis, rheumatoid arthritis, or disseminated gonococcal infection
- Any prosthetic joint that becomes hot and swollen is a surgical emergency (prosthetic joint infection) requiring urgent orthopaedic involvement
Frequently Asked Questions
"Why do you never start allopurinol during an acute gout attack?"
Rapidly lowering serum urate mobilises urate crystals from tissue deposits, which can paradoxically trigger further inflammation and prolong or worsen the acute attack. Urate-lowering therapy is started only once the acute flare has fully resolved, with anti-inflammatory cover in the initial months to prevent flares as urate levels fall.
"How do you tell gout and pseudogout apart under the microscope?"
Gout crystals (monosodium urate) are needle-shaped and negatively birefringent under polarised light. Pseudogout crystals (calcium pyrophosphate) are rhomboid-shaped and positively (weakly) birefringent. This distinction is definitive and is the gold-standard way to differentiate the two conditions.
"A patient with known gout presents with a hot swollen knee and a temperature of 38.5°C, what do you do?"
Treat this as suspected septic arthritis until proven otherwise, regardless of the known gout history. Aspirate the joint urgently for microscopy, Gram stain, and culture, and do not delay empirical IV antibiotics if the patient is systemically unwell, following local sepsis protocols. A known diagnosis of gout does not protect against a co-existing septic joint.