Ultrasound diagnoses gout

Researchers have found a way to use ultrasound as a diagnostic tool for gout. The noninvasive modality could serve as a potential supplement to blood, urine, and joint fluid tests, which don't always provide a definitive diagnosis.

Gout is a form of arthritis caused by uric acid crystals deposited on the connective tissue of joints, particularly small joints like the toes and fingers. Attacks of gout come and go, often with long symptom-free periods in between attacks. Left untreated, the uric acid crystals may grow into large, solid tophi. Screening options for gout include tests that look for excess uric acid in blood and urine, but levels may not be unusually high if crystals have already formed. Joint fluid samples may detect crystals, but sampling joint fluid can be painful. And none of these tests is definitive

The study was published in Rheumatology on April 27 by Dr. Ralf G. Thiele and Dr. Naomi Schlesinger in the rheumatology division of the University of Medicine and Dentistry of New Jersey. They studied ultrasound exams of 37 joints from 23 patients with confirmed cases of gout. They also studied ultrasound exams of 33 joints from 23 randomly selected patients with other rheumatic conditions as controls.

In 92% of the joints with gout, the researchers found an irregular hyperechoic band, called the double contour sign, over the edge of the cartilage. None of the control exams showed this sign.

Tophaceous material was also visible in all the ultrasound exams of gout patients' toes and fingers as hypo- or hyperechoic inhomogeneous material surrounded by a small anechoic rim. None of the controls showed these signs of tophi.

Erosion in the soft tissue of the joints next to tophaceous material was seen in 65% of toe joints with gout and 25% of finger joints with gout. One control patient with psoriatic arthritis showed similar signs of erosion in a toe joint.

The researchers concluded that ultrasound could reliably detect the deposition of urate crystals on cartilage as well as tophi and erosions typical of gout.