Gout: punched-out erosions with overhanging edges and tophi, the double-contour sign on ultrasound, urate coloured on dual-energy CT; CPPD: chondrocalcinosis of the menisci and TFCC and the SLAC wrist pattern.
Orient first
- Gout erosions are juxta-articular with sclerotic overhanging edges; joint space preserved until late.
- Double-contour sign = urate on the cartilage surface; DECT colour-codes urate (beware artefact at nail beds and skin).
- CPPD: chondrocalcinosis (menisci, TFCC, pubic symphysis) and degenerative change in unusual joints (radiocarpal, patellofemoral).
Acquire the study
- Radiographs of the affected joints and both feet.
The manoeuvre
- Radiograph: punched-out erosions with overhanging edges, first MTP.
- Tophi on the radiograph: soft-tissue densities, may calcify.
- Chondrocalcinosis on the knee and wrist radiograph: meniscal and TFCC linear calcification (CPPD).
What confirms it
- Crystals on joint aspiration; imaging supports when aspiration is not possible.
What licenses you to exclude it
- No double contour and no DECT urate make gout less likely but do not exclude early disease.
The classic misread
- Calling tophaceous gout a bone tumour.