Piriformis Syndrome Workup

Updated: Feb 23, 2023
  • Author: Shishir Shah, DO; Chief Editor: Sherwin SW Ho, MD  more...
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Imaging Studies

Imaging studies include the following:

  • Computed tomography (CT) scanning

    • CT scans may demonstrate a large mass anterior to the piriformis muscle.

    • More importantly, CT scans can be used to identify spinal stenosis or arthritic changes.

  • Magnetic resonance imaging (MRI)

    • MRI findings can rule out other causes of back pain, such as a herniated disc, spinal tumor, or abscess.

    • The piriformis muscle also can appear enlarged on T1- or T2-weighted images.

  • Electromyography (EMG)

    • EMG can also be performed to determine neurologic or muscular changes.

    • In piriformis syndrome, EMG findings in the gluteus minimus, gluteus medius, and tensor fasciae latae muscles are normal.

    • In piriformis syndrome, abnormal patterns are found in the gluteus maximus and piriformis muscles.

    • In the case of a herniated disc, all muscles that are posteriorly and anteriorly innervated should be affected.

    • With a herniated disc, a significant delay in the Hoffman reflex, or H-reflex (motor nerve fiber response after activation of afferent sensory spindle fibers), in the affected limbs is often present during EMG. [7]



Diagnostic injection of the piriformis syndrome trigger point is performed as follows:

  • Localize the pain at the sciatic notch, transvaginally or transrectally.

  • Draw 5-7 mL of 2.5% lidocaine or bupivacaine into a 10-mL syringe with a 27-gauge needle.

  • Prepare a sterile field and apply Betadine over the trigger-point area.

  • Inject the anesthetic after aspirating to confirm that the needle is not in a vascular bundle.

  • Remove the needle, and apply pressure to the area to ensure hemostasis.

  • Allow the patient to ambulate and to abduct and externally rotate the affected leg.

  • If the pain subsides, the likely cause of the pain is piriformis syndrome.

  • This procedure is both therapeutic and diagnostic.