SNOWMASS, COLO. — Pyriformis syndrome as a cause of low back pain is greatly overdiagnosed, Dr. Zacharia Isaac asserted at a symposium sponsored by the American College of Rheumatology.
“First of all, true pyriformis syndrome involves an entrapment of the sciatic nerve as it goes through the pyriformis muscle. And that's rare anatomically. Only 7% of people actually have their sciatic nerve going through the pyriformis as opposed to running next to it. So only 7% of the population should even be potentially subject to pyriformis syndrome,” said Dr. Isaac, who is the medical director of the comprehensive spine care center at Brigham and Women's Hospital, Boston.
Pyriformis syndrome is often the diagnostic label applied in patients with pain limited to the gluteal region. But as an entrapment neuropathy, real pyriformis syndrome should produce radicular-sounding symptoms into the thigh and calf as well as the buttock. Typically there is painful flexion, adduction, and internal rotation. Palpation over the sacral notch and gluteal region can often produce the buttock and leg pain.
What's often labeled pyriformis syndrome is much more commonly undiagnosed proximal radicular pain or referred pain from an arthritic facet joint or disk, according to Dr. Isaac.
“If it's just gluteal pain then it's just that: that pain in the butt where you don't know if it's coming from the back through a referral mechanism or it's the proximal extent of radicular pain. The buttock is a nebulous area,” he explained.
“Probably the most common scenario is the patient has had a herniated disk earlier on. It injured the nerve root, the nerve root is now chronically injured, the herniation has resorbed, and now you still have sciatic symptoms down the leg,” the physician continued.
Audience members asked Dr. Isaac what he thinks of the practice of some orthopedists who believe prolonged spasm of the pyriformis muscle is a common cause of pyriformis syndrome. They'll do a diagnostic injection of local anesthetic into the muscle and often follow up with botulinum toxin type A.
“Botox in the pyriformis is a step too far, in my mind,” Dr. Isaac replied. “I think weakening and deadening a muscle or going in surgically to release the pyriformis muscle doesn't make much sense for this sort of debatable diagnosis. But a local anesthetic block to enable you to say, 'Yes, this is pyriformis syndrome,' and then give some stretching exercises for the pyriformis—that makes sense.”
On rare occasions he will obtain a magnetic resonance image of the pelvis in highly refractory patients who don't seem to have a lot of psychologic overlay. The chief purpose is to learn if the sciatic nerve actually pierces the pyriformis and edema is present in the muscle.
“The additional reassuring part of getting the study is now I know there is no soft tissue sarcoma or intra-abdominal pathology pressing on the sacral plexus. So for those reasons I find an MRI useful, but if you got it in everybody complaining of neuropathic pain with no clear abnormality in their lumbar spine you'd be spending a lot of money for nothing,” said Dr. Isaac.
Dr. David Borenstein of George Washington University, Washington, commented that rheumatologists see another category of patients who have what they consider pyriformis syndrome, but of a reversible kind.
“We do see some people with spondyloarthropathy who have pseudosciatica which causes pyriformis irritation. You treat their disease and the radiculopathy goes away. And they really don't have any disk disease,” he explained.