Snapshot A 70-year-old man presents to the emergency department for severe left knee pain. Medical history is significant for hyperparathyroidism managed with bisphosphonates. On physical exam, the left knee is erythematous, warm, enlarged, and tender to palpation. Radiography of the affected joint demonstrates chondrocalcinosis. Joint aspiration demonstrates a leukocyte count of 2800/mm3 with 50% polymorphonuclear cells. Polarized microscopy shows weakly positively birefringent rhomboid crystals. Introduction Clinical definition a metabolic arthropathy due to deposition of calcium pyrophosphate dihydrate (CPP) in connective tissue Epidemiology risk factors radiographic CPP deposition increases with age Etiology CPP deposition in joints Pathogenesis aging and/or genetic factors may result in increased adenosine triphosphate breakdown producing inorganic pyrophosphate CPP is produced after inorganic pyrophosphate binds with calcium CPP then deposits in cartilage and synovial fluid leading to a synovitis Associated conditions hemochromatosis hyperparathyroidism hypomagnesemia can be seen in Gitelman and Bartter syndrome joint trauma, surgery, and severe medical illness these conditions can provoke an acute attack Prognosis acute attacks typically resolve in 10 days patients may experience functional limitation due to joint damage may resemble osteoarthritis or rheumatoid arthritis Presentation Symptoms asymptomatic (most cases) acute attack (pseudogout) typically affects the wrists, knees, and metacarpophalangeal joints are clinically indistinguishable from gout symptoms and physical exam findings include pain erythema warmth swelling disability of the affected joint "pseudo-rheumatoid arthritis" inflammatory arthritis symptoms joint pain and morning stiffness pyrophosphate arthropathy resembles osteoarthritis Imaging Radiography indication to assess the affected joint findings chondrocalcinosis and degenerative changes chondrocalcinosis appears as hyperdensities that are punctate and linear Studies Arthrocentesis confirms the diagnosis Gram stain and culture should always be performed since infection could co-exist leukocyte count is 2,000-100,000/mm3 > 50% polymorphonuclear cells polarized microscopy demonstrates weakly positively birefringent rhomboid crystals blue when parallel to light and yellow when perpendicular to light Differential Gout differentiating factor polarized microscopy demonstrates negatively birefringent crystals more commonly affects the first metatarsophalangeal (MTP) joint Treatment Conservative observation indication in patients with asymptomatic chondrocalcinosis Medical nonsteroidal anti-inflammatory drugs (NSAIDs) indication an initial treatment option for pseudogout colchicine indication an initial treatment option for pseudogout glucocorticoids indications injections of the affected joint is typically used in patients with < 2 involved joints oral medications are typically used in patients with > 2 involved joints Complications Joint damage