Thumb Motion Tips Off Doctors to Problem of Missing Tendon
Doctors in Japan report two cases of a very rare thumb condition. In this condition, one thumb tendon on the back of the hand is missing, and another tendon is in its place. Both patients in this study had wrist pain on the thumb side of the wrist. The pain was made worse by moving the thumb.

A diagnosis could be made based on pain, swelling, and a positive Finkelstein's test. Finkelstein's test is done by making a fist with the thumb wrapped inside the fingers. The wrist is then tilted down toward the floor. Painful symptoms on the thumb side of the wrist suggests a tendonitis of two tendons in the wrist. These tendons are the abductor pollicis longus (APL) and the extensor pollicis brevis (EPB). The condition is called de Quervain's disease.

In the first case, treatment for de Quervain's with cortisone injections didn't change the patient's symptoms. During surgery the doctors found that the EPB was missing. In its place was the extensor pollicis longus (EPL) tendon. The EPL is usually on the index finger side of the thumb. It attaches to the back of the last knuckle of the thumb. Contracting the EPL straightens the tip of the thumb. The doctors pulled on the tendon, and found it did indeed pull the tip of the thumb back.

The second case was another patient diagnosed with de Quervain's disease. The diagnosis was made based on the painful symptoms along the thumb side of the wrist. Again cortisone injections didn't relieve the pain. When the patient could no longer extend her thumb, surgery was done. The doctors remembered the first case and looked closely at this patient's anatomy.

They found that the EPB was missing. Again, the EPL took the place of the EPB in the wrist. The EPL was tightly bound down by the lining (tendon sheath) around it. The surgeons released the tendon sheath. Immediately, the patient had complete relief from her symptoms.

The authors report that it's possible to have what looks like tendonitis of the EPB when it's really the EPL. This happens when the EPB is missing and the EPL is in its place instead. The doctor can avoid making the wrong diagnosis. Swelling and tenderness are located further up the wrist and more toward the center than in de Quervain's disease.

The key is in the tip of the thumb. Since the EPL straightens the tip, any problems with this movement can alert the doctor. If a patient has painful symptoms like de Quervain's disease but can't straighten the tip of the thumb, the problem isn't de Quervain's. In such cases the problem is more likely tendonitis of the EPL and not the EPB.
Yukio Abe, MD, PhD, et al. Extensor Pollicis Longus Tenosynovitis Mimicking de Quervain's Disease Because of Its Course Through the First Extensor Compartment: A Report of 2 Cases. In The Journal of Hand Surgery. March 2004. Vol. 29A. No. 2. Pp. 225-229.