Pseudogout is a form of microcrystal synovitis caused by the deposition of calcium pyrophosphate dihydrate crystals in the synovium. For this reason, it is now more correctly termed acute calcium pyrophosphate crystal deposition disease.

Pseudogout is strongly associated with increasing age. Patients who develop pseudogout at a younger age (e.g. < 60 years) usually have some underlying risk factor, such as:

• haemochromatosis
• hyperparathyroidism
• low magnesium, low phosphate
• acromegaly, Wilson's disease

Features

• knee, wrist and shoulders most commonly affected
• joint aspiration: weakly-positively birefringent rhomboid-shaped crystals
• x-ray: chondrocalcinosis
  • in the knee this can be seen as linear calcifications of the meniscus and articular cartilage

Management

• aspiration of joint fluid, to exclude septic arthritis
• NSAIDs or intra-articular, intra-muscular or oral steroids as for gout