Copyright 2009
Definition
Pseudogout of the knee joint is also known as calcium pyrophosphate disease (CPPD) is is a metabolic disease affecting larger joints such as knees, wrist, and hips (smaller joints are affected as well, but less commonly). It is the result of deposition of calcium pyrophosphate dihydrate in and around joints, especially in articular and fibrocartilage. CPPD is usually asymptomatic, but there typically are radiographic changes (ie, chondrocalcinosis) which define the disease. It is the most common cause of secondary metabolic osteoarthritis.
Calcium pyrophosphate deposition is characterized by onset in the 5th decade or later and has no predilection for race but a 1.4/1 female to male ratio shows a slight increased incidence in the female population. Acute attacks are termed pseudogout and can be quite painful. They often times will mimic the symptoms of gout or a septic knee with pain, swelling, and redness being the most common symptoms.
The mechanism behind the disease hasn’t been fully explained, but there is an increased adenosine triphosphate breakdown with resultant increased inorganic pyrophosphate in the joints which occurs as a result of aging, genetic factors, or both. Changes in the cartilage matrix may play an important role in promoting CPPD deposition. Rare hereditary forms of CPDD occur, generally inherited in an autosomal dominant mode.
Overactivity of enzymes that breakdown triphosphates, such as nucleoside triphosphate pyrophosphohydrolase, has been observed in the cartilage of patients with CPDD. Therefore, inorganic pyrophosphate can bind calcium, leading to CPPD deposition in cartilage and synovium. Hyaline cartilage is affected most commonly, but fibrocartilage, such as the meniscal cartilage of the knee, also can be involved.
Diagnosis is made based on plain x-rays, lab work, and history and exam. Acute pseudogout can occur in about 25% of patients with CPPD and patients will have an acutely inflamed joint with swelling, effusion, warmth, tenderness, and pain on range of motion similar to acute gouty arthritis.
Imaging includes the use of plain x-rays. MRIs are not needed in diagnosing or treating this disease.
Treatment for pseudogout includes observation for patients that are asymptomatic. When acute attacks of pseudogout occur, it is essential to rule out a septic knee which needs to be treated aggressively with irrigation and debridement. Acute pseudogout can be treated with NSAIDs, icing, activity modification until the symptoms resolve, and occasionally aspiration.
References
http://emedicine.medscape.com/article/808628-overview