Ganglion Cyst Pressure Motor Branch of the Median Nerve
After Passing through the carpal tunnel, the median nerve gives a branch on the radial side called the recurrent motor branch. The recurrent motor branch innervates the abductor pollicis brevis, the flexor pollicis brevis (superficial head), and the opponens pollicis muscles. The recurrent motor branch of the median nerve also has multiple variations of the nerve; 50% are extraligamentous with recurrent innervation, 30% are subligamentous with recurrent innervation and 20% are transligamentous with recurrent innervation.
So, when the carpal tunnel is released, it is important that the transverse carpal ligament is cut far ulnar as to avoid cutting the recurrent motor branch of the median nerve. Patients who undergo this procedure will get motor symptoms after the carpal tunnel is released.
There is another entity similar to this entity, and these are the patients that have symptoms similar to carpal tunnel syndrome, but their presentation is not classic. These patients may need to get an MRI or ultrasound to check the carpal tunnel areas.
Carpal tunnel syndrome is a clinical diagnosis. The patient will have night pain, and a self-administered hand diagram would show this area of involvement. The patient may also have thenar atrophy, weakness, or clumsiness of the hand. Another diagnostic step is the compression test. This is the most sensitive test, and it will be positive. The Pahlen’s test, Tinel’s sign, and the Semmes Weinstein test will also all be positive. Some physicians believe that EMG does not really increase the diagnostic value of these tests (if there is a combination of the tests), and surgery should be done, regardless if the EMG is normal or not.
The problem comes when patients have weakness and atrophy of the thumb muscles, but the provocative and sensory tests for carpal tunnel syndrome are negative. In this case, and MRI will be done to rule out pressure on the motor branch of the median nerve. In this case, a ganglion cyst will probably the factor found causing pressure on the motor branch of the median nerve.
