What's Making My Ring and Little Finger Go Numb?

Two microsurgeons use this case study of a fellow physician (anesthesiologist) to explain the diagnostic process of cubital tunnel syndrome or CubTS. Cubital tunnel syndrome is a condition that affects the ulnar nerve where it crosses the inside edge of the elbow.

The symptoms are very similar to the pain that comes from hitting your funny bone. When you hit your funny bone, you are actually hitting the ulnar nerve on the inside of the elbow. There, the nerve runs through a passage called the cubital tunnel. When this area becomes irritated from injury or pressure, it can lead to cubital tunnel syndrome.

For this patient (the anesthesiologist), numbness and tingling of the ring and little fingers developed. At first, the symptoms were on and off. Sometimes there was also pain along the medial (inside next to the body) border of the elbow. Gradually, the symptoms became constant and weakness of the hand muscles developed. Grip strength decreased and the patient reported increased clumsiness when using that hand.

The cause of the symptoms was not obvious. The diagnostic team got busy trying to confirm a tentative diagnosis of cubital tunnel syndrome. First, they checked the past medical history. Was there anything that could contribute to these symptoms (e.g., previous elbow fracture, fall on the elbow, sleeping on that arm, repetitive elbow flexion)? The answer was 'no'.

The physician examining the anesthesiologist performed several clinical tests to check for possible mechanical irritation, friction, or compression on the ulnar nerve. These tests are referred to as provocative maneuvers.

For example, gentle tapping over and around the nerve were positive for causing the symptoms to get worse. Putting the elbow in a fully flexed (bent) position for three minutes is positive if again the position causes the ring and small fingers to go numb. The anesthesiologist/patient had a positive flexion test.

Other typical clinical testing includes pressing on the nerve (called palpation) to see if it is tender. Palpation while moving the elbow may also show that the nerve moves in and out of the natural groove (cubital tunnel) in the bone where it should remain all the time. This type of nerve subluxation (partial movement out of the groove) or dislocation (nerve displaced out of the groove completely) can contribute to the problem.

The authors of this case report took the time to review published studies on cubital tunnel syndrome. They were looking for any evidence that these tests are actually sensitive enough and reliable enough to make a confirmed diagnosis of cubital tunnel syndrome.

They found a wide range of results reported by various surgeons conducting these tests on normal adults (normal meaning there were no previous symptoms of cubital tunnel syndrome). Some researchers just evaluated one test at a time. Others tried combining different tests to see if the results were more reliable that way.

One of the biggest problems in coming to any conclusions about testing for cubital tunnel syndrome is how much variation there is in conducting the tests. Judging the results (called interrater reliability) is another important factor. The lack of interrater reliability is one reason why these tests can't be used alone to make the diagnosis.

There are electrodiagnostic tests that can be done. Nerve conduction studies check the speed at which the nerve transmits signals. Damaged, compressed, or irritated nerves may have abnormal conduction times. But studies of the validity and reliability of nerve conduction tests show limited sensitivity for these tests.

What about imaging studies such as ultrasound, MRI or CT scans? There haven't been a lot of studies in this area. So far, it looks like MRIs show nerve compression before it is evident using electrodiagnostic testing.

But the best imaging choice may be ultrasound. Bouncing sound waves off the tissues creates a picture on a computer screen. It allows the surgeon to see any changes in the cubital tunnel. Ultrasound images reveal bone spurs or ganglions that are pressing on the nerve. Ultrasound also provides a view of the nerve to see if it is subluxed or dislocated from the cubital tunnel.

On the basis of their literature review on the diagnosis of cubital tunnel syndrome, these two microsurgeons make the following recommendations:

  • More research is needed to support the use of provocative and electrodiagnostic tests.
  • Studies to determine the presence of cubital tunnel syndrome in the general population are also needed. This type of testing would show how reliable (predictive) the test procedures really are.
  • It would be helpful to know if some tests are more accurate than others -- either when used alone or when combined with another test (or several other tests).
  • Evidence-based treatment will need a clinical prediction rule. Clinical prediction rules help determine the likelihood someone has cubital tunnel syndrome based on symptoms, clinical findings, and valid diagnostic tests. This approach is based on probabilities rather than certainties.

    Until this type of information is available, surgeons are advised to continue using a method of probability to make the diagnosis. In other words, if the current provocative tests in use are positive, the likelihood (probability) of cubital tunnel syndrome goes up. Advanced imaging tests aren't needed unless there is some suspicion of a tumor or other mass.

    Treatment begins with conservative (nonoperative) care including medications (antiinflammatories) and putting the elbow in an extension splint at night. Surgery is considered only if conservative care fails after at least a month's trial period.

    References: Richard L. Hutchinson, MD, and Ghazi Rayan, MD. Diagnosis of Cubital Tunnel Syndrome. In The Journal of Hand Surgery. September 2011. Vol. 36A. No. 9. Pp. 1519-1521.