Piriformis Syndrome: A Review
Abstract & Commentary
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports that he receives grant/research support from Pfizer and is on the speaker's bureau of Athena Diagnostics.
Synopsis: Healthy skepticism is warranted before making or accepting a diagnosis of piriformis syndrome.
Source: Kirschner JS, Foye PM, Cole JL. Piriformis syndrome, diagnosis and treatment. Muscle Nerve 2009;40; 10-18.
Utilizing "piriformis syndrome" (PS) and "botulinum toxin" as search terms, and eliminating case reports and reviews, PubMed identified 11 articles related to the history, examination, findings, diagnosis, and therapy of PS. First described in 1928 but coined by Robinson in 1947, PS denotes a constellation of features including direct buttock trauma, gluteal atrophy and radiating leg pain, a palpable sausage-shape gluteal mass, positive straight-leg raise sign, and worsening pain with bending or lifting. Weakness and sensory loss are unusual. Entrapment of the sciatic nerve, as it traverses the inferior border of the piriformis and emerges through the greater sciatic notch, is believed causative. Responsible annually for perhaps 6%8% of sciatica in the United States, PS is a clinical diagnosis of exclusion. Certain maneuvers are felt to assist in its diagnosis. Provocative movements that exacerbate the pain include: forceful internal rotation of the hip in the supine position, thereby stretching the piriformis muscle (Freiberg's maneuver); abducting the hip in the seated position contracting the piriformis (Pace maneuver); or stretching the piriformis by placing the hip in the FAIR position (flexed, adducted, internally rotated).
Imaging studies including CT, MRI, and ultrasound are primarily useful to exclude other conditions such as spinal stenosis, disc herniation, endometriosis, tumor, aneurysm, and abscess, but piriformis anomalies such as an accessory or enlarged muscle are reported. Standard nerve conduction studies (NCS) and needle electromyography are usually normal but magnetic NCS has demonstrated slowed motor nerve conduction velocity in the gluteal portion of the sciatic nerve on L5, but not S1, nerve root stimulation. Treatment includes pain control through anti-inflammatory agents, anti-convulsants, and tricyclic anti-depressants, piriformis stretching exercises to relieve nerve compression, injection of the piriformis with local anesthetics, corticosteroid, or botulinum toxin to relax the muscle, and ultimately surgical splitting of the muscle in refractory cases.
Commentary
Essentially unaddressed in this review is whether PS truly exists. Even when surgically explored, early reports noted no striking features or anomalous course of the sciatic nerve that reputedly is the likely setting for PS. Although an incidence of 6%8% among back pain patients is cited, the actual perceived prevalence is closer to 0.5%1% in an orthopedic practice, even less in a non-referral practice.1 Few patients in the literature meet all criteria for PS, and patients with other disorders share symptoms and signs. Considering it lies deep to the massive glutei, it is baffling how trauma to the buttocks would selectively affect the piriformis or that its spasm is truly palpable.2 Anatomically, gemellus superior muscle spasm could be equally culpable.2 Stretching of the obturator internus muscle can also compress the sciatic nerve, as documented intra-operatively in a 44-year-old man with sciatica of unknown etiology.3 Provoking pain by both contracting (Pace maneuver) and stretching the muscle (Freiberg's maneuver) appears contradictory, as does the recommendation that piriformis stretching exercises relieves nerve compression. Significantly, none of these tests have been validated.3 Local anesthetic or steroid injection into the piriformis or sciatic region will relieve symptoms regardless of cause, and can hardly be of any diagnostic value. Cadaver studies have shown that anatomical causes for the piriformis syndrome are rare and precise workup to uncover more common etiologies is recommended.4 Healthy skepticism is warranted before making or accepting this diagnosis.
References
1. Goldner JL. Piriformis compression causing low back and lower extremity pain. Am J Orthop 1997;26: 316-318.
2. Campbell WW, Landau ME. Controversial entrapment neuropathies. Neurosurg Clin N Am 2008;19;597-608.
3. Murata Y, Ogata S, Ikeda Y, et al. An unusual cause of sciatic pain as a result of the dynamic motion of the obturator internus muscle. Spine Journal 2009;9(6): e16-e18.
4. Windisch G, Braun EM, Anderhuber F. Piriformis muscle: clinical anatomy and consideration of the piriformis syndrome. Surg Radiol Anat 2007;29;37-45.
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