By Reuben Sloan, MD
What is piriformis syndrome?
Piriformis syndrome is what we, in medicine, call a “zebra.” You might ask, “What does that mean?” I will get to that later in this article.
To fully understand what piriformis syndrome is requires breaking down the words.
The piriformis is a muscle in the inferolateral (lower outer part) of the buttock and is mainly responsible for rotating the hip and leg externally (outwardly).
A syndrome is defined as a collection of signs and symptoms associated with a specific health-related issue.
So, piriformis syndrome is a collection of signs and symptoms attributable to the piriformis muscle. More specifically, it’s sciatica that is not attributable to the low back. In other words, it is not attributable to a herniated disc, stenosis (tight nerve canal(s) due to arthritis) or some other nerve compressive condition originating in the back. Rather, it is attributable to an issue in or abnormality of the piriformis muscle. It is extremely rare for the lumbar spine to not be responsible for sciatica, which leads to piriformis syndrome being termed a “zebra.”
During many arduous years of medical education, medical students and residents are trained to think in terms of differential diagnoses. When a patient presents with a collection of signs and symptoms, we are taught to go through a mental checklist of all of the possible diseases or conditions that could be responsible, even unusual or rare ones. While we were encouraged to (and often rewarded for) come up with unusual or exotic “differentials,” our professors would often redirect our tangential thinking by saying, “When you hear hoofbeats, think horses, not zebras!” Meaning, common causes are far more likely to be responsible—common is common, unusual is rare.
What causes piriformis syndrome?
• Microtrauma/repetitive trauma due to prolonged sitting on hard surfaces
• Overuse of the piriformis muscle due to long-distance walking or running
• Direct compression or “wallet neuritis” compression of the piriformis and, hence, the sciatic nerve due to sitting on a fat wallet
• Anatomical variations
• Typically, both divisions (peroneal and tibial) of the sciatic nerve pass underneath the piriformis muscle (89%)
• One of the divisions runs superior to (above) or through the piriformis muscle (11%)—and is more susceptible to compression
How common is piriformis syndrome?
It depends on the source, but prevalence is estimated to range from 0.3 to 6%, or anywhere from three cases per 1,000 to six cases per 100. Regardless of what the actual prevalence is, it is not very common. Nevertheless, someone with pain radiating down the leg will have piriformis syndrome.
Signs and symptoms:
• Tenderness and pain in the buttock area
• Sciatic-like pain with tingling and numbness and/or weakness radiating down the back of the thigh, calf, and foot
• Worsening of symptoms after prolonged sitting, climbing stairs, walking or running
• While signs and symptoms are often identical to sciatica attributable to the spine (aka lumbar radiculopathy, or nerve- root irritation or impinging in the spine) there are a couple of defining features seen only in piriformis syndrome
• Sciatica-type symptoms in the absence of a herniated disc, stenosis or other condition of the lumbar spine on magnetic resonance imaging (MRI)
• Electrodiagnostic (EMG/Nerve Conduction Study) revealing sparring of muscles proximal to (above) the piriformis muscle, namely the lumbar paraspinals and some of the gluteal (buttock) muscles
Treating piriformis syndrome:
• Anti-inflammatory medications: nonsteroidal anti-inflammatory drugs (NSAIDs) and/or oral steroids
• Stretching program, mainly focused on the piriformis muscle, often physical therapist directed
• Therapeutic ultrasound and/or iontophoresis (the use of electric current to transport solubilized medication across the skin barrier)
• Injection(s), typically of an anti-inflammatory medication such as methylprednisolone (cortisone), preferably with guidance (ultrasound or fluoroscopy) in an attempt to relax the piriformis can be utilized if other, non-interventional treatments fail
• Alternative treatments such as acupuncture and chiropractic care may be appropriate in some cases
• Botulinum toxin (BOTOX) injections have been used in rare, extremely refractory cases to relax the piriformis muscle for an extended amount of time when other injection treatments have provided relief, albeit temporary relief
Preventing piriformis syndrome:
• Avoid the causes mentioned above, including prolonged sitting on a hard surface or thick wallet, long-distance running or walking
• Maintain piriformis muscle flexibility
• Stretch frequently! It’s better to stretch 20 times for one minute than one time
for 20 minutes
Though horses are far more common, zebras do exist!