Red flags
- Fever + acutely inflamed joint(s) -> aspirate. Septic arthritis can be polyarticular in ~15% (especially RA, immunosuppression, IVDU)
- New murmur + polyarthralgia + fever -> infective endocarditis (blood cultures and echo BEFORE steroids)
- Persistent synovitis >6 weeks -> refer urgently; the window of opportunity closes at ~3 months
- Weight loss, night sweats, lymphadenopathy -> malignancy, lymphoma, paraneoplastic
- Purpura + neuropathy + renal impairment -> systemic vasculitis
- Haemoptysis, dyspnoea or new renal failure -> pulmonary-renal syndrome
- Rash + fever + arthritis in a returned traveller -> arboviral infection, acute HIV, meningococcaemia
- Sudden onset in a patient on immunosuppression -> opportunistic infection, not a flare
- Corticosteroid before a diagnosis destroys the diagnostic yield of aspiration, serology and biopsy
Differential by mechanism2 exam ›
By tempo
- Acute (<6 weeks): viral (parvovirus B19, rubella, hepatitis B, HIV seroconversion, Ross River and Barmah Forest virus, chikungunya), reactive arthritis, acute rheumatic fever, gout/CPPD, serum sickness, drug reaction, early presentation of a chronic disease
- Chronic (>6 weeks): RA, psoriatic arthritis, SLE and other CTDs, chronic tophaceous gout, OA, spondyloarthritis, sarcoidosis
By joint distribution - the single most useful discriminator
| Pattern | Think |
|---|---|
| Symmetrical small joint, MCP/PIP, DIP SPARED | Rheumatoid arthritis, SLE (non-erosive), viral |
| DIP INVOLVED | Psoriatic arthritis, osteoarthritis, gout |
| Asymmetric, lower limb, large joint | Spondyloarthritis - reactive, enteropathic, psoriatic |
| Axial + peripheral + enthesitis + dactylitis | Spondyloarthritis |
| Migratory | Acute rheumatic fever, gonococcal, endocarditis, SLE, Lyme |
| Additive | RA, psoriatic |
| 1st MTP, midfoot, asymmetric, episodic | Gout |
Deforming polyarthropathy - the exam differential
- Rheumatoid arthritis - fixed deformity, erosive, MCP/PIP
- Psoriatic arthritis - DIP, nail change, pencil-in-cup, ray pattern
- Chronic tophaceous gout - tophi, punched-out erosions with overhanging edges
- Primary generalised OA - Heberden and Bouchard nodes
- Erosive/inflammatory OA - central gull-wing erosions
- Jaccoud's arthropathy (SLE) - *reducible* deformity, non-erosive
- Ankylosing spondylitis, reactive arthritis, multicentric reticulohistiocytosis
Not to be missed
- Septic arthritis (polyarticular in ~15%), infective endocarditis, gonococcal arthritis
- Malignancy - paraneoplastic polyarthritis, leukaemia (especially in children), hypertrophic pulmonary osteoarthropathy
- Haemochromatosis - 2nd and 3rd MCPs with hook osteophytes
- Sarcoidosis - Lofgren syndrome
- Amyloidosis, acromegaly, hypothyroidism
- Fibromyalgia - widespread pain, normal examination and markers; frequently coexists and confuses assessment
Focused history
Characterise the arthritis
- Number of joints, symmetry, distribution, DIP involvement
- Tempo: acute vs chronic; migratory vs additive vs intermittent
- Duration >6 weeks? - the threshold that makes chronic inflammatory arthritis likely
- Morning stiffness duration - >30-60 min = inflammatory; <30 min = mechanical
- Better or worse with use - inflammatory improves with movement; mechanical worsens
- Night pain, swelling seen by the patient, functional impact
Systematic screen for the underlying disease
- Skin: psoriasis (including scalp, umbilicus, natal cleft), photosensitive rash, purpura, erythema nodosum, tophi, nodules
- Nails: pitting, onycholysis
- Eyes: red painful eye (uveitis), dry eyes, scleritis
- Bowel: diarrhoea, blood, weight loss
- Genitourinary: urethritis, cervicitis, recent STI
- Mucosa: oral and genital ulcers
- Sicca, Raynaud phenomenon
- Respiratory: dyspnoea, cough (ILD)
- Neurological: numbness, weakness, mononeuritis
Exposures and drivers
- Recent infection - GI, GU, viral illness, sore throat 2-4 weeks earlier
- Travel and mosquito exposure - Ross River virus and Barmah Forest virus are common in Australia; chikungunya, dengue
- Sexual history - gonococcal, HIV, reactive arthritis
- Drugs: diuretics (gout), hydralazine, procainamide, minocycline, TNF inhibitors (drug-induced lupus), statins, checkpoint inhibitors
- Alcohol, IV drug use, tick bite
- Family history - psoriasis, IBD, autoimmune disease, gout
- Occupational, smoking
Focused examination
General
- Fever, weight loss, cachexia, lymphadenopathy, splenomegaly
- Rash - distribution, photosensitivity, purpura, erythema nodosum, keratoderma blennorrhagicum
- Nails, scalp, umbilicus, natal cleft - hidden psoriasis
- Eyes - conjunctivitis, uveitis, scleritis, dry eyes
- Mouth - ulcers, dryness
Joints
- Confirm SYNOVITIS, not arthralgia: boggy swelling, warmth, effusion, stress pain
- Distribution: MCP/PIP vs DIP; symmetry; squeeze test across MCPs and MTPs
- Deformity - and is it reducible? (Jaccoud's reduces; RA does not)
- Enthesitis - Achilles insertion, plantar fascia, epicondyles
- Dactylitis - whole-digit sausage swelling
- Spine - Schober's test, occiput-to-wall, chest expansion, SI joint tenderness
The discriminating extras
- Elbows: rheumatoid nodules vs gouty tophi vs psoriatic plaques
- Ear helix: tophi
- Cardiac: murmur (endocarditis, aortic regurgitation in AS), pericardial rub
- Chest: fine crepitations (ILD)
- Abdomen: splenomegaly (Felty, sarcoid, lymphoma), hepatomegaly
- Neurological: mononeuritis multiplex, proximal weakness (myositis), carpal tunnel
- Nailfold capillaroscopy - dilated loops and dropout in scleroderma-spectrum disease
Investigation strategy
First line - everyone
- FBE (anaemia, leukopenia, thrombocytosis, lymphopenia in SLE), ESR and CRP
- UEC, LFT, calcium, urate
- Urinalysis with microscopy - dysmorphic RBC and casts in vasculitis or lupus nephritis
- Rheumatoid factor AND anti-CCP - only in a genuine inflammatory joint presentation
- ANA - only if there are CTD features; a positive result in a low-probability patient causes more harm than good
Targeted
- Joint aspiration if there is an effusion
- Cell count and differential, Gram stain and culture, polarised light microscopy
- *Always exclude sepsis before attributing to crystals - the two coexist*
- Fluid WCC: <2000 non-inflammatory; 2000-50,000 inflammatory; >50,000 suspect sepsis
- Blood cultures if fever, murmur or immunosuppression
- Viral serology: parvovirus B19 IgM, hepatitis B and C, HIV, Ross River and Barmah Forest virus (Australia), EBV, rubella
- Anti-streptolysin O / anti-DNase B if migratory arthritis with fever
- ENA panel, anti-dsDNA, C3/C4 if the ANA is positive
- HLA-B27 if inflammatory back pain or asymmetric lower-limb oligoarthritis
- Ferritin and transferrin saturation - haemochromatosis with MCP arthropathy
- CK if weakness; TSH; protein electrophoresis if age >50 with unexplained inflammation
- Faecal calprotectin if bowel symptoms; STI screen (NAAT) if reactive arthritis suspected
Imaging
- X-ray hands AND feet - the feet erode before the hands and are often asymptomatic
- RA: juxta-articular osteopenia + marginal erosions at 2nd/3rd MCPs, uniform joint space loss
- PsA: normal density, fluffy periostitis, pencil-in-cup
- Gout: preserved joint space, punched-out erosions with overhanging edges, normal density
- OA: LOSS - Loss of joint space, Osteophytes, Subchondral cysts, Subchondral sclerosis
- Ultrasound with power Doppler - confirms synovitis when examination is equivocal; detects enthesitis and erosions early
- MRI - bone marrow oedema, the precursor to erosion; sacroiliac joints for axial disease
- CXR - ILD, hilar lymphadenopathy (sarcoid), malignancy
Management
1. Decide inflammatory vs non-inflammatory first
- Inflammatory: morning stiffness >30-60 min, better with use, swelling, raised CRP/ESR
- Non-inflammatory: mechanical pattern, normal markers, no synovitis
2. Exclude infection before immunosuppressing
- Aspirate any effusion; blood cultures if febrile
- *Do not give corticosteroid until sepsis and endocarditis are excluded*
3. Symptom control while investigating
- NSAID (with gastroprotection and renal caution)
- Intra-articular corticosteroid for a dominant joint once sepsis is excluded
- Short-course oral prednisolone only once the diagnosis is reasonably secure
- Analgesia, splinting, physiotherapy
4. Refer early
- Persistent synovitis >6 weeks warrants urgent rheumatology referral
- The window of opportunity in RA is the first ~3 months - do not wait for a positive serology or an erosion
5. Treat the specific diagnosis
- RA -> treat-to-target with methotrexate + bridging glucocorticoid
- Psoriatic arthritis -> by domain
- Spondyloarthritis -> exercise + NSAIDs, then TNF or IL-17 inhibitor
- Gout -> flare therapy + urate-lowering to target
- CTD -> hydroxychloroquine backbone + organ-directed therapy
- Viral -> reassure and treat symptomatically; most resolve within 6 weeks
- Reactive arthritis -> NSAIDs, treat the trigger infection, sulfasalazine if persistent
6. In parallel, always
- Cardiovascular risk assessment (inflammation is an independent risk factor)
- Bone protection if glucocorticoid is likely to continue
- Vaccination and TB/hepatitis screening BEFORE immunosuppression
- Smoking cessation, exercise, weight management
Traps
- *Arthralgia is not arthritis* - if there is no synovitis, resist serology and steroid
- Ordering an ANA or RF in a patient with fatigue or non-inflammatory pain - the false positive rate exceeds the disease prevalence and generates years of unnecessary follow-up
- Crystals in the joint do not exclude sepsis - gout and septic arthritis coexist, especially in the elderly
- A normal ESR and CRP do not exclude inflammatory arthritis - normal in ~25% of axSpA, ~50% of PsA, and often in SLE (where CRP is characteristically normal even in flare)
- Giving steroid before aspirating destroys the microbiological yield
- Forgetting the feet - MTP erosions precede hand erosions and MTP squeeze tenderness is often the only sign
- Missing psoriasis - look at the scalp, umbilicus, natal cleft and nails
- Attributing new joint pain in an immunosuppressed patient to a flare - consider opportunistic infection
- Seronegative does not mean not RA - ~30% are seronegative; treat the clinical picture
- A high CRP in an SLE patient means infection or serositis, not lupus activity
- Corticosteroid withdrawal arthralgia in an IBD or PMR patient masquerades as a flare
Talk track
1. Inflammatory or not
- "My first question is whether this is genuinely inflammatory - more than an hour of morning stiffness, better with use, with demonstrable synovitis - because that decides everything downstream."
2. Pattern recognition
- "Then the pattern: symmetrical small joints with DIP sparing points to rheumatoid; DIP involvement to psoriatic, gout or osteoarthritis; asymmetric lower-limb large joints with enthesitis to a spondyloarthritis."
3. Exclude the dangerous mimics
- "Before I immunosuppress anyone I aspirate any effusion for cell count, Gram stain and crystals, and if there is fever or a murmur I take blood cultures and an echocardiogram - polyarticular sepsis and endocarditis both present exactly like this."
4. Targeted investigation
- "I would send FBE, CRP, ESR, renal and liver function, urate, urinalysis, RF and anti-CCP, and X-ray hands and feet - the feet erode first. ANA only if there are connective tissue features."
5. Refer within the window
- "If the synovitis has persisted beyond six weeks I refer urgently, because the window of opportunity in rheumatoid arthritis is the first three months and outcomes are determined by how quickly a DMARD is started."
8 of 8 sections written · drafted 2026-09-04