General MedicineTier 1Approach to a presentation

Undifferentiated presentations - pain and swelling

Red flags

Hot, swollen single joint with fever - septic arthritis until excluded, needs urgent aspiration
Calf swelling + pain + risk factors - DVT until excluded
Compartment syndrome features (pain out of proportion, pain on passive stretch, paraesthesia) - surgical emergency
Rapidly spreading erythema/swelling with systemic toxicity - necrotising fasciitis
Swelling + neurovascular compromise distally

Joint-localised

Septic arthritis (single hot joint, fever - aspirate before antibiotics if possible), crystal arthropathy (gout - podagra classic; pseudogout), reactive arthritis, inflammatory arthritis flare (RA, psoriatic)

Limb swelling

DVT, cellulitis, lymphoedema, chronic venous insufficiency, ruptured Baker's cyst (mimics DVT), compartment syndrome (post-trauma/reperfusion)

Soft tissue

Systemic causes of swelling

Heart failure, nephrotic syndrome, hypoalbuminaemia, lymphatic obstruction (malignancy, filariasis)

Onset (sudden vs gradual), single joint vs polyarticular, migratory pattern
Trauma, recent surgery/immobility (DVT/compartment risk), fever, systemic symptoms
Prior gout/pseudogout, psoriasis, IBD, recent GI/GU infection (reactive arthritis)
Risk factors for VTE (malignancy, OCP, immobility, prior VTE, family history)

Joint - warmth, effusion, range of motion, erythema
Limb - measure circumference, compare sides, Homans sign unreliable, distal neurovascular status
Compartment syndrome - pain on passive stretch (most sensitive early sign), firm compartment, paraesthesia (late)

Joint aspiration - cell count, gram stain/culture, crystal analysis - mandatory if septic arthritis considered, do this before/alongside starting antibiotics where feasible
FBE, CRP/ESR, uric acid (unreliable acutely in gout - can be normal during a flare)
Doppler ultrasound for suspected DVT; Wells score to guide pre-test probability and D-dimer use
X-ray for trauma/chronic joint changes; compartment pressure measurement if compartment syndrome suspected

Septic arthritis: urgent joint washout/drainage + IV antibiotics - orthopaedic emergency, do not delay for imaging
Gout flare: NSAID, colchicine, or corticosteroid (oral/intra-articular) - do not start urate-lowering therapy during an acute flare (can prolong it); continue if already established
DVT: anticoagulation (DOAC first-line for most), compression, investigate provoking factors/malignancy screen if unprovoked
Compartment syndrome: urgent fasciotomy - a clinical diagnosis, do not wait for pressure measurement if classic features present
Cellulitis/abscess - antibiotics +/- drainage as appropriate

Uric acid can be normal or low during an acute gout flare - don't use it to exclude the diagnosis acutely
A ruptured Baker's cyst mimics DVT closely (calf pain and swelling) - ultrasound distinguishes them
Starting allopurinol during an acute gout flare can worsen and prolong it
Compartment syndrome is a clinical diagnosis in classic presentations - don't wait for pressure measurements if the picture is clear

"A hot single joint gets aspirated before I commit to a diagnosis, not treated empirically."
"I never start urate-lowering therapy during the flare itself."

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