The area affected most often is the ulnar nerve. This is the nerve along the outside edge of the wrist and hand. Pressure on the palm of the hand from long periods on the bike (racers) and/or rough terrain (mountain bikers) can cause this problem. This is because the area covering the ulnar nerve and the ligaments that enclose the nerve are thin. The nerve is also fairly close to the surface. That's why many bikers wear special protective gloves. There's usually a gel pad or foam built into the gloves along the wrist border.

The handlebars of the bike can also be padded or the angle changed to keep pressure off the palm pads. It might be a good idea to invest in some protective gear for your son. If the symptoms don't go away with some modifications, he may have to take a break until the nerve heals.

If he already has the right gear and rest has not helped, then it may be time to see a doctor. Seek out an orthopedic doctor who has specialized as a hand surgeon if one is available in your area.