Patients with suspected carpal tunnel syndrome may be better served by undergoing ultrasound as an initial diagnostic modality before magnetic resonance imaging (MRI) and electromyography (EMG) are pressed into service, according to a team of Polish investigators whose findings were presented here June 9^th at the 6^th Annual European Congress of Rheumatology (EULAR).

"Both MRI and electromyogaphy are unpleasant for patients, as well as time-consuming, expensive, and not always available," said principal investigator Anna Ciechomska, MD, PhD. Ultrasound accurately identifies the hallmark findings of carpal tunnel syndrome, is easier for patients to tolerate, and is less expensive, she added. Dr. Ciechomska is a professor of internal medicine and rheumatology at the Military Medical Institute in Warsaw, Poland.

She and her co-investigators wanted to know whether ultrasound would accurately identify the features of nerve compression in patients with carpal tunnel syndrome. They obtained ultrasound images of 126 wrists in 52 patients who had been diagnosed with carpal tunnel syndrome by EMG. They also obtained ultrasound images of the wrists of 22 healthy people. The unit used was an Aspen (Accuson) equipped with a linear, wideband transducer at 6 to 11 MHz.

Dr. Ciechomska and her team assessed the echogenicity, thickness, and structure of the median nerve and noted visible causes of the compression. They also measured the cross-sectional area of the nerve at the level of entrance to the carpal tunnel. They excluded subjects in both the carpal tunnel syndrome and control groups who had anatomical variations of the nerve, such as high nerve division.

The investigators found that 83% of wrists with carpal tunnel syndrom had less echogenicity and also had an enlargement of the median nerve proximal to the carpal tunnel. The average cross-sectional area of the median nerve at the entrance to the carpal tunnel was 16.0 mm², compared to an average of 8.3 mm² in the healthy patients (P > .000005). When the investigators used EMG for a reference, they found that a cross-sectional area of the nerve of 9.3 mm² had a sensitivity of 92%, a specificity of 98%, and was 97.8% accurate in diagnosing the nerve compression.

In patients with carpal tunnel syndrome, the investigators observed that 92.1% had flattening of the nerve and that the nerve's structure was blurred within the carpal tunnel in 43.4%. Carpal tunnel patients also had nerve enlargement and a 44.7% decrease in echogenicity distal to the tunnel.

In 20 of the 126 wrists, ultrasound alone was able to identify possible causes of nerve compression, according to Dr. Ciechomska. Therefore, she and her co-investigators concluded that ultrasound would be an appropriate imaging modality to use first in all patients with suspected carpal tunnel syndrome, and, if further details were needed, MRI and EMG should be used.