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Is the Mystery of Anterior Interosseous Palsy Solved?

Sometimes orthopedic surgeons have to be like Sherlock Holmes, the fictional detective written about by Sir Arthur Conan Doyle back in the 1800s. Patients come in with all types of pain and symptoms. The diagnosis isn't always obvious at first.

Take the patient featured in this article for example. She was a 36-year-old woman without significant pain or discomfort. But suddenly her handwriting started to get worse and worse. She didn't have any numbness or tingling to suggest a nerve problem. The usual suspect (ulnar nerve) tested okay.

By systematically checking each one of the muscles in the forearm and wrist, the surgeon was able to find the clues needed to identify the anterior interosseous nerve (AIN) as the culprit. Because the patient could not make the "OK" sign with the thumb and first (index) finger, the surgeon knew the anterior interosseous nerve was compressed or pinched.

Once a diagnosis has been made, the next question in the mystery is what to do about it? Anterior interosseous nerve palsy or syndrome is a fairly uncommon problem. There isn't a lot of research to help the surgeon know what treatment is best. And with fairly mild nerve compression like this, it could get better on its own.

So the next question is: how long can the patient wait to see if recovery occurs before having surgery? And finally, will surgery really fix the problem? When surgeons are faced with these kinds of questions, they can search the medical literature for evidence to favor one approach over another.

The two surgeons involved in this case did just that. They found quite a few studies with small numbers of patients (six to 20) and compiled their results. There was agreement that full recovery occurs in about 12 to 18 months. Younger patients (those who started developing anterior interosseous palsy before age 40) recovered faster.

Some patients were treated with vitamin B12 and electrical stimulation therapy performed by a hand therapist (Physical Therapist or occupational therapist). The patients receiving this type of nonoperative care were tested every month with electromyography
Some studies showed that untreated, a few patients went on to develop paralysis and disability from unresolved nerve compression. Recovery is more likely when the nerve compression is partial or incomplete. Compression severe enough to cut the nerve off completely is less likely to recover and more likely to need surgery.

When surgical care is required, the surgeon attempts to remove pressure from the nerve. This procedure is called decompression. Any scar tissue, fibrosis, or connective tissue that may have formed around the nerve is carefully stripped away. The process of cutting the nerve sheath (protective covering around the nerve) lengthwise is called neurolysis.

There are some confusing issues that are difficult to sort out regarding anterior interosseous syndrome. For one thing, the nerve does seem to recover spontaneously without surgical intervention, whereas other similar nerves in the forearm and wrist (e.g., ulnar, median, radial nerves) do not naturally heal.

Comparing results of natural healing versus surgical intervention is difficult when the cause of anterior interosseous syndrome could be from trauma versus an unknown cause. Maybe one type of nerve compression responds differently than another. Studies have not been done to compare the two.

Based on the evidence that anterior interosseous nerve palsy has a natural history of spontaneous recovery, and the fact that this particular patient came to them after only three months of symptoms, the surgeons followed the wait-and-see approach. They checked on her every few months to see how she was doing. In the end, surgery was not needed.

The authors suggest that perhaps the patients who develop anterior interosseous nerve palsy don't really have a compression neuropathy. Since most of them seem to get better on their own with time, it's possible there is a temporary nerve dysfunction of some type. If that's the case, then surgery could make things worse instead of better.

Unless there is complete loss of nerve transmission due to some type of trauma, infection, or tumor, surgical treatment is not advised. Patients should be followed carefully and monitored for recovery. Electrodiagnostic testing can be done to look for signs of recovery and then repeated every four to six weeks to observe the progression of improvement in nerve function.

Whether or not treatment is helpful during the recovery phase (e.g., with vitamin B, electrical stimulation, or other methods) was not investigated or reviewed in this report. Future studies are needed to compare various nonsurgical approaches to find the best healing modality.

Perhaps the body's own innate ability to heal is all that's needed to foster recovery.
If that is true, we might say this deduction is obvious or to quote Sherlock Holmes who often said to his friend Dr. Watson, "It's elementary, my dear Watson".

Reference: Ying Chi, MD, and Neil G. Harness, MD. Anterior Interosseous Nerve Syndrome. In The Journal of Hand Surgery. December 2010. Vol. 35. No. 12. Pp. 2078-2081.

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