Repetitive motion injuries, which have long afflicted desktop and laptop computer users, are invading the mobile handheld world.

Earlier this year, a consumer alert was released warning users of small electronic gadgets that heavy thumb use could lead to painful swelling of the sheath around the tendons in the thumb.

The BlackBerry, which debuted in 1999, employs a full QWERTY keypad for thumb typing to automatically send and receive e-mail. About 2.5 million people currently use Blackberries, more than double from a year ago.

Musculoskeletal disorders, which include repetitive strain injuries, accounted for a third of all workplace injuries and illnesses reported in 2003.

Treatment for BlackBerry thumb may include receiving massage therapy treatments to relax the overworked muscles. Wearing a splint and applying ice to the affected area is an option as well. If the pain persists, doctors may opt to inject the thumb area with a cortisone shot.