What is the role of botulinum toxin in the treatment of piriformis muscle syndrome?

Updated: Mar 11, 2019
  • Author: Heather Rachel Davids, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Answer

PMS is a controversial myofascial pain condition that presents with seemingly bizarre symptoms. Patients typically are female, have a recent history of trauma to the buttocks or pelvis (usually from a fall), and complain of deep pain in the buttocks and hip, radiating into the thigh or even into the leg and foot. These characteristic signs and symptoms may be from sciatic nerve compression by a contracted piriformis muscle as the nerve passes through the pelvis. Although some clinicians believe this diagnosis is controversial, several peer-reviewed articles cite clinical, anatomic, and electrophysiologic evidence for this distinct condition causing low back and leg pain.

On clinical examination, pressure over the buttocks at a point midway between the sacrum and greater trochanter of the hip reproduces the patient's pain complaint. Since the piriformis muscle is so deep, some clinicians say that palpation of this TrP can be performed properly only by rectal or vaginal examination. Palpation of the TrP on the posterolateral portion of the rectal (or vaginal) vault elicits pain at the site of compression and refers pain either into the thigh or down the leg.

The Beatty maneuver (see image below) also is a helpful clinical method of reproducing the patient's pain in this condition. [39] The patient is asked to lie on the nonpainful side and abduct the thigh by moving the painful leg off the table. This maneuver effectively contracts the piriformis muscle and should reproduce the patient's pain in the buttocks; however, since the syndrome essentially causes sciatic nerve compression at the level of the hip, other causes of sciatica should be ruled out (eg, herniated lumbar disc).

The Beatty maneuver. The Beatty maneuver.

One helpful diagnostic aid is electromyography. In a patient with radiculopathy and sciatica, an electromyographic examination should reveal abnormal spontaneous electrical activity in the extensor muscles of the back. In piriformis syndrome, the electromyogram (EMG) is classically normal. If there is enough sciatic nerve compression to cause axon loss, the abnormalities should be in the muscles distal to the piriformis, and no electrical activity should be seen in the back muscles. A special nerve conduction test, H reflex, has been reported to demonstrate abnormalities in piriformis syndrome when abduction, internal rotation, and flexion of the thigh compress the sciatic nerve; however, this result has not been reproduced by other clinicians. Making a reliable diagnosis in piriformis syndrome is almost impossible; thus, treatment also is difficult.

In some patients, if conservative treatment of piriformis syndrome fails, local injections of anesthetics and/or steroids should be considered. Surgical resection of the piriformis muscle is an additional option; however, some patients may gain short-term benefits from local TrP injections into the muscle without responding to other treatment for long-term pain control. This subset of patients may benefit from treatment with BoNT-A. (See image below.)

Left piriformis muscle, posterior view. Inject 100 Left piriformis muscle, posterior view. Inject 100 U botulinum toxin type A (BOTOX®) diluted in 3 mL saline into the area marked with an 'X' when guided by fluoroscopy.

A limited number of studies assess the efficacy of botulinum toxin in the treatment of piriformis syndrome. [8] For example, Childers and colleagues reported findings from a double-blind placebo-controlled crossover pilot study of BoNT-A injection for refractory piriformis syndrome in 9 subjects. [40] All patients in this study reported pain intensity greater than 3/10 on visual analog pain scales (VASs) after at least 3 months of failed conservative treatment for PMS prior to enrollment. Symptomatic muscle in each patient was injected with 100 U BoNT-A or placebo (saline), using fluoroscopic and electromyographic guidance. Ten weeks later, saline or BoNT-A injections were repeated. The main outcome measures were VAS of pain intensity, distress, spasm, and interference with daily activities.

At baseline, no differences were detected between groups, yet significant (P< .05) differences were observed between the average of 2 minimum VAS at baseline and the average of 2 minimum VAS (in all categories) under the 10-week treatment (BoNT-A) arm, but not the 10-week placebo arm. In addition, BoNT-A treatment average was improved significantly (P = .0273), from baseline/washout average in VAS of daily activities. Data also suggested that a significant (P = .0547) improvement in VAS in muscle spasm (P = .0547) occurred in the BoNT-A group but not in the placebo group. Taken together, these findings demonstrated that, compared to intramuscular saline, BoNT-A injections reduced some, but not all, reports of pain attributed to chronic PMS.


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