Pyriformis muscle syndrome: CT/MR findings in the percutaneous therapy with botulinic toxin

The aim of our study was to evaluate the diagnostic capabilities of computed tomography (CT) and magnetic resonance (MR) imaging in pyriformis syndrome (PS) and the long-term outcomes of CT-guided percutaneous treatment with botulinum. PS is a cause of sciatica and disability. The pain is usually increased by muscular contraction, palpation or prolonged sitting.

Thirty-four patients suffering from PS, suspected on the basis of clinical and electrophysiological criteria and after imaging examinations had excluded other causes of sciatic pain, had positive lidocaine tests and were treated by intramuscular injection of botulinum toxin type A (BTX-A) under CT guidance. MR sequences was performed in nine patients before treatment and after three months to evaluate the extent of muscle denervation.

In 30 cases relief of symptoms was obtained after 5-7 days. In four patients insufficient pain relief warranted a second percutaneous treatment which proved clinically successful. No complications or side effects were recorded after BTX-A injection. The MR examination demonstrated a change in signal intensity of the muscle in seven patients due to denervation, whereas in the remaining two cases only atrophy was detected. Larger series are necessary to confirm these preliminary results.

CT-guided BTX-A injection in the pyriformis muscle is an emergent and feasible technique that appears to yield excellent local therapeutic effects without the risk of imprecise injection.