Pseudogout

Definition/diagnostic criteria Pseudogout, also known as calcium pyrophosphate deposition (CPPD), is characterised by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the joint tissues. The British Society of Rheumatology outlines that for a definitive diagnosis, the identification of CPPD crystals in the synovial fluid is necessary. The crystals are positively birefringent and rhomboid-shaped under polarised light microscopy.

Epidemiology Pseudogout is more prevalent in the elderly, with incidence increasing with age. It has been found to affect approximately 3% of people aged 60-69, and this prevalence rises to around 50% in individuals aged 85 and above (in terms of radiological evidence of the problem). Both men and women are affected, although some studies suggest a slight male predominance.

Diagnosis
Clinical features: Patients with pseudogout typically present with acute onset of pain, swelling, and redness in one or more joints. The knee is the most commonly affected joint, but wrists, shoulders, ankles, and elbows can also be involved. The acute attacks can be precipitated by trauma, surgery, or severe medical illness. Between attacks, patients may be asymptomatic or have persistent joint pain and stiffness.

Investigations: Joint fluid analysis is the gold standard for diagnosis, with the identification of positively birefringent, rhomboid-shaped CPPD crystals necessary for a definitive diagnosis. Plain radiographs can show chondrocalcinosis, which is the deposition of calcium pyrophosphate crystals in the cartilage, but this finding is not specific for pseudogout and can be seen in other conditions. Other typical abnormalities on blood tests may include elevated inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), though these are not specific for pseudogout.

Treatment The treatment of pseudogout aims at relieving pain and inflammation and preventing future attacks. Non-steroidal anti-inflammatory drugs (NSAIDs) are the first-line treatment for acute attacks. For patients who are unable to take NSAIDs, colchicine can be used. Intra-articular corticosteroids can be effective for pain relief in a single affected joint. For chronic, symptomatic CPPD, low-dose colchicine or NSAIDs may be used for prophylaxis. Joint aspiration can help relieve pressure and pain in affected joints.

Prognosis The prognosis for pseudogout is variable. Some patients may experience only one or few attacks, while others may have recurrent episodes. In some cases, persistent joint inflammation can lead to joint damage and chronic pain. Early diagnosis and appropriate management are key to improving outcomes.