The piriformis muscle is situated in the pelvis and is an important structure as the main nerve to the leg, the sciatic nerve, passes through it. Increase in size of the piriformis muscle, excessive spasm or variations in the manner in which the nerve passes through the muscle may result in leg pain, similar to sciatica.
A radiologist may assist in this clinical setting by injecting a small dose of medication containing a paralysing agent under CT control. This inactivates the piriformis muscle for 3-6 months, without resulting in leg weakness or impaired activity. At this point, the muscle usually has wasted to result in improvement or resolution of symptoms.
Once the medication wears off however, symptoms may recur, at which point the procedure is simply repeated. If symptoms are severe, then surgery may be required. For those patients wishing to proceed to surgery early, an injection may still be of use to first confirm the diagnosis, as the condition is often difficult to diagnose. A good response to an injection is a useful predictor of surgical success.
Thoracic Outlet Syndrome
Spasm of muscles in the neck, usually the scalenus anterior or medius muscles, may result in poor circulation to the hand and unusual neurological symptoms. This is characteristic of the condition known as thoracic outlet syndrome.
By using ultrasound or CT guidance to selectively inject these muscle with paralysing medication, the muscles are paralysed for 6 months. This can be curative, however, in many instances the pain can recur once the medication ceases to work. As for piriformis syndrome, the injection is still useful as it predicts which patients are more likely to respond to surgery.
- Danielson K, Odderson IR. Botulinum toxin type A improves blood flow in vascular thoracic outlet syndrome. Am J Phys Med Rehabil 87(11):956-9, 2008
- Jordan SE, Ahn SS, Freischlag JA, Gelabert HA, Machleder HI. Selective botulinum chemodenervation of the scalene muscles for treatment of neurogenic thoracic outlet syndrome. Ann Vasc Surg 14(4):365-9, 2000
Referring doctors are welcome to discuss with our radiologists the imaging and interventional radiology needs of their patients and whether a muscle spasticity injection is suitable for their patient’s medical condition.