Piriformis Syndrome

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Piriformis Syndrome
Epidemiology	Unknown
Causes	Entrapment neuropathy
DDX	Lumbar radicular pain, lumbar somatic referred pain, sacroiliac joint pain.
Treatment	Physical therapy, injections, piriformis tenotomy

Piriformis Syndrome is a very controversial entity that describes extra-spinal entrapment neuropathy of the sciatic nerve by the piriformis muscle. The condition is also known as Deep Gluteal Syndrome, but some denote Piriformis Syndrome a subset of Deep Gluteal Syndrome. On the spectrum of anecdotal fiction to scientific fact it sits more on the side of the former. See Marin et al for a recent open source review

Controversy

It is the opinion of the author and the general consensus of Musculoskeletal Medicine specialists in New Zealand that this condition is over-diagnosed in New Zealand. The flaws in logical reasoning are usually of a material nature. These are the most common reasons that the author has seen for a patient being incorrectly diagnosed as having piriformis syndrome:

• Misreading lumbar MRI imaging. For example not looking at the lateral recesses - where stenosis there is a common cause for radicular pain. Another example is incorrectly believing that proper nerve compression is required for radicular pain to occur. Nerve root compression causes radiculopathy, nerve root inflammation with or without compression is a cause of pain. I.e. "no nerve root compression" does not mean that the pain isn't arising from the nerve roots.
• Not being familiar with the concept of somatic referred pain where pain is arising from structures such as a lumbar disc, lumbar facet joint, or sacroiliac joint.
• Not being aware that buttock pain is extremely common in radicular pain syndromes from disc disease.
• Putting too much emphasis on the straight leg raise test, thinking that a negative test excludes disc disease as a cause.

Complicating matters is that there is no gold standard for diagnosis and so different studies use different inclusion criteria. The research literature is dominated by case studies and review articles and flawed reasoning is a common feature. Using Bogduk's Postulates, the concept fails in postulates 2, 3, and 4.

Epidemiology

The author has not found any reliable sources evaluating the prevalence of this condition in those with chronic low back pain or sciatica. A 1983 study by P Hallin is often quoted by review authors stating that piriformis syndrome accounts for between 6% to 8% of all sciatica cases. However in the Hallin article there is no discussion or study of the prevalence whatsoever.

Aetiology

The sciatic nerve typically passes immediately anterior to the piriformis muscle. Sciatic nerve entrapment may occur subsequent to buttock trauma or sprain of the piriformis muscle which is purported to cause perineural fibrosis. Another mechanism is through anatomical variation where the sciatic nerve branches pass through a bifid piriformis muscle. Both the piriformis muscle and sciatic nerve exit the pelvis through the greater sciatic notch. An accessory piriformis muscle can be implicated.

During downhill running or sprinting, the piriformis muscle undergoes eccentric contraction and some runners may develop the syndrome via this mechanism.

Clinical Manifestations

Buttock pain that increases with sitting is reported to be a common presenting symptom. However this can also occur with lumbar radicular pain. The "wallet sign" has been described which describes a male patient finding he cannot sit on his wallet without symptoms occurring. The patient may have radicular pain.

Diagnosis

The Freiburg test is performed with placing the hip in extension and internal rotation, and then resisting external rotation. A positive test is the production of pain or radicular symptoms. It has questionable clinical value.

The Pace test has the patient in a seated position. The patient then resists abduction and external rotation. A positive test is the production of pain or typical symptoms. This test also is of questionable clinical value.

Endoscopic evaluation has been used for diagnosis but this also has questionable value.

Another diagnostic method is the injection of local anaesthetic into the piriformis muscle with a positive result being resultant pain reduction by a significant but arbitrary percentage.

Imaging

MRI and x-rays can help evaluate for other causes of symptoms. Often MRI of the piriformis muscle is normal, however an accessory piriformis muscle can be identified, and if there is relatively acute sprain or inflammation then there may be an increased T2 signal. Neurophysiology studies are not typically helpful. In one small study, ultrasound evaluation showing increased piriformis thickness was found to be helpful in diagnosis in those without lumbosacral radiculopathy on MRI.

Treatment

Treatment options include physiotherapy, corticosteroid injections, botulinum toxin injections, and piriformis tenotomy.

Resources

See review by US physiotherapist here

Summary

• Piriformis syndrome probably exists but it is over-diagnosed, there are numerous other more common causes that can explain the symptoms in almost all individuals
• There is no convincing evidence that the piriformis muscle is anything more than a very rare cause of sciatic nerve compression
• Evidence is based on flawed studies and flawed reasoning
• Deep gluteal syndrome is a better descriptive term to describe non-discogenic radicular pain with a gluteal origin because the anatomical conflict is not always the piriformis muscle
• Injections and surgery are performed too commonly and without adequate justification

Literature Review

Literature Review

Reviews from the last 7 years: review articles, free review articles, systematic reviews, meta-analyses, NCBI Bookshelf

Articles from all years: PubMed search, Google Scholar search.

TRIP Database: clinical publications about evidence-based medicine.

Other Wikis: Radiopaedia, Wikipedia Search, Wikipedia I Feel Lucky, Orthobullets,