Internal Medicine

0521779407-C04 CUNY1086/Karliner 0 521 77940 7 June 14, 2007 20:37

Crystal-Induced Arthritis 433

■Conditions leading to underexcretion of uric acid

➣Renal failure

➣Drugs: diuretics, cyclosporine

■Metabolic diseases for CPPD: hyperparathyroidism, hypothy-

roidism, hemochromatosis, gout, amyloidosis

Signs & Symptoms

■Acute: hot, red, swollen, exquisitely tender joint (85% mono-

articular); joint effusion

■Chronic: indolent polyarthritis may lead to deformities

■Tophi are irregular hard nodular deposits of MSU in subcutaneous

tissue of fingers, toes, ulnar surface

tests

Lab Tests

■Serum uric acid

➣Usually elevated in acute gouty arthritis (∼85%), less often in

alcoholics

➣Invariably elevated in chronic tophaceous gout

➣Asymptomatic hyperuricemia is common, esp. w/ diuretics;

requires no treatment

■For CPPD: serum Ca, P, Mg, alkaline phosphatase, transferrin satu-

ration, TSH

■Aspirate synovial fluid

➣WBC usually >10,000/mm3; if >100,000/mm3, suspect infection

➣Polarized light microscopy

Strongly negatively birefringent needle-shaped crystals of

MSU are diagnostic of gout

Weakly positive birefringent rhomboid crystals are diagnostic

of CPPD disease

Crystals may be found in asymptomatic joints

■Needle & aspirate nodular subcutaneous tophus, examine for MSU

crystals

Radiographs

■Soft tissue swelling, effusion in acute arthritis

■Juxta-articular “punched-out” erosive lesions in digits w/ topha-

ceous gout

■In CPPD disease: chondrocalcinosis, punctate calcifications of hya-

line or fibrocartilage of knees, wrists, hips