The Median Nerve
The median nerve, which derives its name from its course along the midline of the forearm, travels from the elbow along this course to the center of the wrist and then into the hand.  In the hand it divides into branches that travel up both sides of the thumb, the index and long fingers, and the radial, or thumb side, of the ring finger.

The Pronator
As the median nerve enters the forearm, it does so by traveling between the two parts of a muscle called the pronator teres muscle.  It then travels down the median, or central, portion of the front of the forearm.  At the wrist it goes through the carpal tunnel and divides into its terminal branches in the palm, which supplies the thumb, the index and long fingers, and half of the ring finger.

Pronator Syndrome
The pronator muscle serves to pronate, or rotate, the forearm and hand to bring the palm of the hand downward.  As the median nerve enters the muscle, there is a fibrous band which can compress the nerve.  Pronator syndrome may arise if there is inflammation in the region where the median nerve travels through the pronator muscle.

Symptoms and Diagnosis
It is often difficult to differentiate this condition from carpal tunnel syndrome, considering that both of them involve the median nerve. Accordingly, much of the symptomatology in the hand is the same for both.  Indeed, the two conditions may coexist, and entrapment of the median nerve may be evident both in the proximal forearm and at the wrist level.
Electrodiagnostic testing may differentiate between the two conditions, however, showing slowing of the median nerve in the proximal forearm rather than in the wrist.
In addition, whereas carpal tunnel syndrome is marked by tenderness at the wrist, pronator syndrome is distinguished by tenderness in the proximal forearm.
Also, with pronator syndrome, the Tinel's sign, a tingling sensation in the distribution of the nerve when tapping on the nerve at the site of entrapment, will be positive in the area just distal to the elbow.  (With carpal tunnel syndrome, this test will be positive with tapping on the nerve at the wrist.)

Treatment
Initially, treatment is conservative, relying on the use of splints (including an elbow splint), rest, a change in the patient's activities, and antiinflammatory medications.  An injection of cortisone may also prove helpful at the elbow region.

Surgery
If conservative measures do not succeed, then surgery in the form of release of the nerve (as it travels through the pronator teres muscle in the forearm) may be needed.  This likely will resolve the compression of the nerve and relieve the symptoms.