Does The Shape Of A Syrinx Predict Improvement?

One of the more frustrating aspects of syringomyelia is that even after successful surgery - meaning restoration of CSF flow and even a reduction in the syrinx - symptoms, especially pain, often don't improve. In fact, if you look at descriptions of the disease from years ago, surgery is described as a way to stop the progression of symptoms, not as a cure.

While it is well known that nerve damage from a traumatic injury doesn't heal well, the exact mechanisms underlying pain associated with a syrinx are not well understood. Some people have syrinxes that go virtually the length of their spine before painful symptoms appear; others suffer from unrelenting pain from what looks like a much smaller syrinx. This lack of knowledge makes it very difficult to predict, on an individual basis, whether pain symptoms will improve after surgery. [Ed note: In making his recommendation for me to have surgery, my neurosurgeon pointed out that if I waited, I wouldn't know at what point the damage to my nerves would be permanent.]

In an attempt to identify factors that influence pain, and pain improvement after surgery, a group from Keio University in Japan, led by Dr. Masaya Nakamura, looked at 25 Chiari related syringomyelia patients they had treated over the past 15 years. The group wanted to know whether age, duration of symptoms (prior to surgery), and/or syrinx shape were related to pain and post-surgical pain improvement. They published their results in the March, 2004 issue of the Journal of Neurosurgery.

The 25 patients ranged in age from 13 to 57 and there were 4 men and 21 women. Eleven patients underwent decompression surgery, 12 patients were treated with shunts (placed directly into the syrinxes) and 2 patients received both. The group was followed for an average of 5 years after surgery.

The researchers divided the patients into two groups: those with pain directly attributable to a syrinx, and those without such pain. They further divided the pain group into those whose pain improved after surgery and those whose pain didn't. In addition, the researchers classified each person's syrinx as either central, enlarged, or deviated (see Fig 1). In all, 17 patients had pain, and 8 had no pain. Of the 17 pain patients, 6 improved after surgery, and 11 did not. Prior to surgery, there were 2 central, 15 enlarged, and 8 deviated syrinxes.

In looking at their data, the group found that age had no relation to whether a person had pain or whether their pain improved after surgery. They did find however, that duration of symptoms was significantly related to both. The average duration of symptoms for the pain group was more than 30 months. In contrast, the average duration for the no pain group was only 15 months. After surgery, the difference was just as striking. The average duration of symptoms for the improved group was about 20 months, while the average for the no improvement group was much higher at about 40 months.

In addition to how long people had had symptoms, syrinx shape also appeared to influence pain. All 8 patients with deviated syrinxes had pain, while only 9 of the 15 enlarged syrinxes, and neither of the two central syrinxes caused pain. Post-surgically, only 1 out of the 8 patients with a deviated syrinx showed any pain improvement. In addition, in three patients, an enlarged syrinx transformed into a deviated syrinx, and in all three cases the patients showed no pain improvement. In total, 10 out of 11 patients who had deviated syrinxes either before or after surgery still suffered from pain after surgery. Unfortunately, the authors did not say whether the type of treatment (decompression, shunt, or both) influenced the pain outcome, so it is not known if there is another variable to account for.

The researchers believe that the deviated syrinxes cause so many problems because their shape means they occupy part of the dorsal horn. Research has shown that damage to this area of the spine causes spontaneous pain and does not heal on it's own.

While the authors don't speculate on this in their paper, it is interesting to note that many researchers believe that given enough time, a syrinx will expand to a maximum and then essentially rupture and begin to reduce in size as the fluid in the syrinx finds a path back into the normal CSF spaces. While not stated explicitly by the authors, it seems likely that the patients with deviated syrinxes also were the ones who had had symptoms for the longest time. One has to wonder if in these cases, the syrinxes were starting to rupture, and it is this process that causes the most damage. Either way, the obvious implication from this work is the importance of early, accurate diagnoses. If these conditions can be identified and corrected early enough, maybe the pain can be stopped before it even begins.


Fig 1
Syrinx Classification

syrinx-size

Central Syrinx - Contained within the central canal

Enlarged Syrinx - One that enlarges the central canal

Deviated Syrinx - A syrinx that bulges in one direction more than others; often into the dorsal horn area of the spine