Arthritis - Calcium Pyrophosphate Deposition Disease
Calcium pyrophosphate deposition disease
Some patients have a disorder similar to gout without synovial fluid uric acid crystals (Fam). Instead they have intracellular calcium pyrophosphate dihydrate crystals, a condition known as pseudogout. Such crystals also occur in osteoarthritis and a range of arthropathies, so that they are an important cause of arthritis in older people.
Causes and disease mechanisms. Calcium pyrophosphate is widely distributed in the body, and it is unclear why it sometimes forms crystals that induce inflammation. These crystals are often associated with metabolic disturbances such as parathyroid disease and a blood disorder known as hemochromatosis. Pathologically the crystals trigger a cascade of inflammatory pathways that mirrors gout.
Pyrophosphate crystals account for up 50 percent of acute attacks of crystal arthritis. Similar crystals are seen in the cartilage of many elderly people, a condition termed chondrocalcinosis. Seen in a minority of seventy year olds but the majority of ninety year olds, its pathological significance is often uncertain.
Clinical features. As is suggested by the name, acute pseudogout is similar to classical gout and can be precipitated by metabolic disturbances such as trauma. The arthritis develops suddenly, with one or several inflamed, painful, swollen, and tender joints. It typically involves knees, shoulders, and wrists. Many patients have recurrent episodes. Some cases have chronic arthritis, often with some joint inflammation occurring over and above osteoarthritis.
Investigations. Intracellular pyrophosphate crystals are visible on polarizing light microscopy of aspirated synovial fluid. X-rays may show chondrocalcinosis, indicating crystal deposition in joint cartilage. Blood tests either are normal or show evidence of mild inflammation with a raised ESR.
Other arthropathies. Other forms of arthritis important in the elderly include septic arthritis and arthritis linked to polymyalgia rheumatica and malignancy. Septic arthritis often complicates pre-existing chronic arthritis, particularly rheumatoid arthritis, and results in an acute exacerbation of joint problems and systemic involvement. Unless there is a high threshold of diagnostic suspicion, it can be difficult to diagnose until the joint sepsis is advanced. Arthritis in polymyalgia rheumatica and malignancy is mild, polyarticular, nonerosive, and seronegative for rheumatoid factor.