What is the workup for piriformis syndrome?

Workup for Piriformis Syndrome

The diagnostic workup for piriformis syndrome should include clinical assessment with specific provocative tests, imaging studies (primarily MRI of the lumbosacral plexus), and consideration of electrodiagnostic studies when the diagnosis remains uncertain.

Clinical Assessment

History

• Buttock pain that worsens with prolonged sitting
• Pain that may radiate down the posterior thigh (sciatica-like symptoms)
• History of trauma or overuse of the gluteal region
• Symptoms exacerbated by activities that involve hip rotation

Physical Examination

• Tenderness on palpation of the sciatic notch and piriformis muscle
• Specific provocative tests:
  • FAIR test (Flexion, Adduction, and Internal Rotation) - reproduction of buttock pain with this maneuver is highly suggestive 1
  • Modified FAIR test - combination of Lasègue sign and FAIR test, shown to be reliable for diagnosis 1
  • Piriformis muscle stretch test - pain with passive internal rotation of the extended thigh

Imaging Studies

1. MRI of the Lumbosacral Plexus (First-line imaging)

   • Can detect anatomic variants or pathology of the piriformis muscle
   • Helps evaluate for compression of the sciatic nerve 2
   • Can rule out other causes of buttock pain and sciatica

2. CT or MRI of the Lumbar Spine

   • To exclude other causes of sciatica such as disc herniation or spinal stenosis 2
   • Should be considered when clinical presentation is unclear

Additional Diagnostic Tests

1. Electrodiagnostic Studies

   • EMG and nerve conduction studies may show:
     • Prolonged H-reflex latency with the FAIR test position
     • Evidence of sciatic nerve compression
   • Should be pursued persistently if initial results are negative but clinical suspicion remains high 3

2. Diagnostic Injections

   • Local anesthetic injection into the piriformis muscle with significant pain relief supports the diagnosis 4
   • Can serve as both diagnostic and therapeutic intervention

Differential Diagnosis to Consider

• Lumbar disc herniation
• Lumbar spinal stenosis
• Sacroiliac joint dysfunction
• Hamstring tendinopathy
• Gluteal muscle strain
• Ischiofemoral impingement

Diagnostic Algorithm

1. Begin with clinical assessment using specific provocative tests (FAIR test, modified FAIR test)
2. If clinical suspicion is high, proceed with MRI of the lumbosacral plexus to evaluate the piriformis muscle and sciatic nerve 2
3. If diagnosis remains uncertain, consider:
   • Electrodiagnostic studies
   • Diagnostic piriformis muscle injection with local anesthetic
4. Rule out other causes with appropriate imaging of the lumbar spine if needed

Common Pitfalls and Caveats

• Piriformis syndrome is often underdiagnosed, comprising between 0.3-6% of all low back pain cases 5
• No single test is pathognomonic; diagnosis relies on a combination of clinical findings, imaging, and response to interventions 4
• Avoid premature surgical intervention before exhausting conservative diagnostic and treatment options 6
• Remember that piriformis syndrome can coexist with other spine pathologies, making diagnosis more challenging

By following this systematic approach to the workup of piriformis syndrome, clinicians can more accurately diagnose this often overlooked condition and initiate appropriate treatment, which may include physical therapy, injections, or in refractory cases, surgical intervention.