Imaging of Musculoskeletal Disorders
Crystal arthropathy

Gout is the most common of the crystal arthropathies. Unlike rheumatoid, gout does not usually have a symmetric distribution. It most commonly affects the first metatarsophalangeal joint.

In patients with acute gout the X-ray may appear normal.

Juxta-articular erosions become visible in chronic gout.

CPPD/Pseudogout

Calcium pyrophosphate dihydrate deposition disease (CPPD) is frequently asymptomatic but may cause an acute arthritis which manifests clinically as pseudogout.

CPPD does not cause erosions as seen in rheumatoid or gout.

CPPD is a common cause of chondrocalcinosis (calcified cartilage) which is most frequently seen in the knee. It has many X-ray features similar to osteoarthritis such as joint space narrowing and sub-cortical cyst formation. Osteoarthritis can also cause chondrocalcinosis, so the two diseases cannot be differentiated on the basis of the presence of these X-ray features. CPPD tends to be more symmetrical and does not have a predilection for weight-bearing joints, as does osteoarthritis.