Pseudogout

definition

· syn. calcium pyrophosphate deposition disease

· inflammatory arthritis of older individuals caused by calcium pyrophosphate dihydrate crystals in the joint

· characteristically accompanied by calcification of articular cartilage (chondrocalcinosis)

epidemiology

· only marginally more common in men (1.5 : 1)

· usually in patient over age 50

· sometimes familial

· may be associated with other disorders

· diabetes

· hypothyroidism

· gout

· hyperparathyroidism

· haemochromatosis

· pernicious anaemia

· onchronosis

pathology

· deposits of calcium phosphate dihydrate crystals in

· joint capsule

· articular cartilage

· fibrocartilage (eg. menisci of knee)

· crystals seen at margin of degenerating cartilage and surrounding lacunae of chondrocytes

pathogenesis

· pyrophosphate generated at chondrocyte surface in abnormal cartilage

· combine with calcium to form crystals

· arthritis initiated by release of crystals from articular cartilage into joint cavity

· results in activation of vasoactive and chemotactic factors

· neutrophils attracted and phagocytose crystals

· leads to release of lysosomal enzymes into joint fluid

· crystal release caused by

· sudden change in ionic calcium and pyrophosphate equilibrium in cartilage (eg. after acute illness or operation)

· physical disruption of cartilage (eg. due to trauma)

· enzymatic degradation of matrix (eg. in inflammatory arthritis)

· chronic chondrocalcinosis predisposes to development of secondary osteoarthritis

· crystals embedded in articular cartilage have dessicating effect

clinical features

Asymptomatic chondrocalcinosis

· majority of people asymptomatic

· commonest incidental finding is calcification of menisci

Pseudogout

· usually affects large joints

· knee most common

· shoulder

· wrist

· usually monoarticular

· rapid onset with peak in 12-36 hrs

· subsides in 1-2 weeks

· may be provoked by

· trauma

· surgery

· illness

Chronic pyrophosphate arthropathy

Pseudo-osteoarthritis

· polyarticular disease like osteoarthritis

· in hips and knees

· in more unusual joints for osteoarthritis

· eg. ankles, shoulders, elbows

· usual features of osteoarthritis

Pseudorheumatoid arthritis

· acute synovitis and chronic arthritis

· rapidly progressive joint destruction

investigations

Laboratory

Synovial fluid

· calcium pyrophosphate dihydrate crystals seen extracellularly and in neutrophils

· rhomboidal in shape

· weakly positively birefringent under polarised light and first-order red compensator

· crystals parallel to compensator are blue

· synovial fluid analysis shows elevated WCC, esp. neutrophils

Radiology

· calcifications in articular cartilage appear as fine linear densities parallel to subchondral bone

· calcifications in fibrocartilage, ligaments and joint capsule appear as more punctate densities

· common fibrocartilage calcifications are

· menisci of knee

· articular disc of distal radioulnar joint

· symphysis pubis

· annulus fibrosis of intervertebral disc

· findings of osteoarthritis usually present

· involves unusual sites such as

· non wt bearing joints

· PF joint in knee

· talonavicular joint in foot

differential diagnosis

· gout

· septic arthritis

· osteoarthritis

· rheumatoid arthritis

treatment

· deposition of crystals cannot be prevented or reversed

· treatment consists of non-steroidal anti-inflammatories

· may use intra-articular corticosteroids