Imaging Studies
Imaging studies include the following:
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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.
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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.
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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]
Procedures
Diagnostic injection of the piriformis syndrome trigger point is performed as follows:
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Localize the pain at the sciatic notch, transvaginally or transrectally.
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Draw 5-7 mL of 2.5% lidocaine or bupivacaine into a 10-mL syringe with a 27-gauge needle.
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Prepare a sterile field and apply Betadine over the trigger-point area.
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Inject the anesthetic after aspirating to confirm that the needle is not in a vascular bundle.
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Remove the needle, and apply pressure to the area to ensure hemostasis.
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Allow the patient to ambulate and to abduct and externally rotate the affected leg.
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If the pain subsides, the likely cause of the pain is piriformis syndrome.
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This procedure is both therapeutic and diagnostic.
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Nerve irritation in the herniated disk occurs at the root (sciatic radiculitis). In piriformis syndrome, the irritation extends to the full thickness of the nerve (sciatic neuritis).
