Carpal tunnel syndrome is a common condition; patients' symptoms can be rapidly relieved by a simple surgical procedure. The diagnosis is often obvious in the presence of a typical history and physical signs. In doubtful cases the surgeon utilises electromyography to confirm the diagnosis. This test, however, is time- consuming and may be unpleasant for the patient. A new test is described using therapeutic ultrasound which is applied to the patient's wrist for a few seconds. A positive response occurs when the patient experiences paraesthesiae or discomfort in the hand in the median nerve distribution. Following a pilot study on 19 patients the test has been further evaluated on a series of 82 patients by comparison with EMG studies. The performance of the ultrasound therapy unit used in the experiments was first fully investigated by measurement of output power and frequency. Animal experiments were conducted to determine the effect of ultrasound on peripheral nerve using the rat sciatic nerve as an animal model. A needle thermistor and hydrophone were used to measure skin temperature and ultrasound intensity during insonation (i.e. exposure of tissue to ultrasound) via a water bag which was used to ensure efficient acoustic coupling. Specimens of sciatic nerve from the insonated rats were examined under the electron microscope. In addition teased specimens of sciatic nerve were prepared and axon counts performed on thin sections. The laboratory work revealed no damage in nerves exposed to normal levels of ultrasound but in the maximal exposure group some focal remyelination was seen The final results of the clinical assessment of the ultrasound test showed a 74% correlation with EMG studies although the latter must remain the investigation of choice. The ultrasound test would seem to have a place as a reasonably accurate, non-invasive screening procedure which can be performed in the clinic with a minimum amount of apparatus
