Radial Tunnel Syndrome Isn't Easy to Diagnose Like Carpal Tunnel Syndrome
Pain, numbness, and tingling in the wrist and hand are common features of compression neuropathies like carpal tunnel syndrome (CTS). But there are two other nerves in the forearm that (when pinched or pressed) can cause similar symptoms: the radial nerve and the ulnar nerve. Radial nerve compression is called radial tunnel syndrome. Problems with the ulnar nerve result in cubital tunnel syndrome.
Radial tunnel syndrome is the focus of this patient report. Because there are no definite tests that prove the patient has radial nerve compression, the surgeon must rely on patient report and clinical findings to make the diagnosis. Knowing this, physicians then ask, What evidence can I rely on? What tests are valid and reliable?
In this case, the patient was a middle-aged male who had a year and a half's worth of elbow pain along the outside of the elbow. There was tenderness with palpation of the common extensor muscles just below the bump on the outside of the elbow. That bump is called the lateral epicondyle. That's a common place for pain to develop with radial tunnel syndrome.
But patients with pain at this place don't always have radial tunnel syndrome. And people with radial tunnel syndrome don't always have pain or tenderness there. Okay -- so, what else might help identify radial tunnel syndrome as the problem?
There's the forearm and finger extension test. The patient attempts to turn the palm up with the elbow extended (straight), a motion called supination. At the same time, the examiner resists the movement. The test is considered positive if there is pain with resistance. Another resistive test involves asking the patient to extend the middle finger. Pain with resistance to this movement is another sign that the radial nerve is entrapped somehow.
With carpal tunnel syndrome, the orthopedic surgeon can order electrophysiologic tests to confirm the diagnosis. A delay in the speed or signal along the nerve to the muscles suggests the median nerve is compromised. But with the radial nerve, electrophysiologic tests are almost always normal even when there's a problem.
Some experts claim that injecting the area around the nerve with a numbing agent is diagnostic. If the pain goes away, then the pain was caused by the nerve being compressed, pinched, or trapped inside scar tissue, muscle, or other layers of tissue. Still others use pressure over the supinator muscle (the one most often contracting around the nerve and compressing it) to reproduce the painful symptoms.
Unfortunately, no one has ever been able to get consisent enough results to consider these tests accurate. There simply aren't reliable enough differences between painful and nonpainful arms to point to one test as the best to diagnose radial tunnel syndrome.
What about imaging studies such as X-rays or magnetic resonance imaging (MRIs)? X-rays have not proven helpful unless there is an obvious bone spur or abnormal anatomy causing nerve compression. The number of those cases is small compared to the total number of patients with radial tunnel syndrome.
So there must be something else to look for. MRIs give additional information that might show mechanical compression as the cause of the problem. But like electrophysiologic testing, imaging studies just don't clearly verify this disease process in the majority of patients.
Where does that leave us? Mostly without an acceptable reference standard for diagnosis of this condition. There's no consensus on reliable tests. And surgeons continue to debate about the availability of evidence and discuss the evidence that has been offered.
Right now, surgeons say they find out for sure after doing surgery to release the posterior interosseous nerve/i>. The posterior interosseous nerve is a part of the radial nerve in the forearm. After the radial nerve has crossed the supinator muscle, it continues on as the posterior interosseous nerve. If the painful symptoms go away after cutting this branch the surgeon can safely assume the diagnosis was radial tunnel syndrome. If not, well then, it must have been something else.
Understandably, patients would prefer to head into surgery knowing it will be successful. That brings us back to the diagnostic drawing board. If researchers can find better, more reliable ways to diagnose the problem before treatment, then patients can be selected for conservative (nonoperative) care or surgical intervention. And patients like the gentleman discussed in this report won't have to suffer 18 months worth of elbow pain before having surgery.
Kimberly I. M. van den Ende, MD, and Scott P. Steinmann, MD. Radial Tunnel Syndrome. In The Journal of Hand Surgery. June 2010. Vol. 35-A. No. 6. Pp. 1004-1006.