Guided CT treatment with botulinic toxin ( Botox ) in patients suffering  from  Pyriform  Muscle Syndrome.
E.Fanucci,V.Varrucciu, L.Bortolotti,C.Iani*,G. Bernardi*, G.Simonetti




The piriformis muscle  sindrome(PMS) is a condition characterizedby pain and paresthesias to the buttock,hip and often radiating to theposterior thight. The cause of PMS may havebeen trauma leading to irritation,inflammation, spasm and hypertrophy ofthe muscle (3,4). Traditional methodsfor relief of this myofascial pain includeslow strechexercise, massage,heat, ultrasound and muscle relaxant medication.Previouslydescribed methods of toxins inoculation include sacro-iliacjoint injection,orsciatic nerveapproach under fluoroscopic guidance anddye study to confirmneedle placement(4).
Other   authors described deep muscle injection under EMGguidanceattrigger point areas (11).
Both fluoroscopic and EMG guidance can help to localize the affectedmuscle but  cannot provide direct vision or precise localization ofthe affected muscle as CT guidance does.
Several therapies has been suggested during the years as to  thissubject. The use of botox is more recent.
Although seven immunologically distinct toxin have since been identified, only types A,B andE have been linked to cases of botulism in humans. Botulin toxin type A, one of trhe most lethal biologic toxin, has been found tobe of therapeutic value in the treatment of focal and segmental dystonia,tremors and spasticity. The list of  treated areas was expanded fromthe initial use of Botox (BTX, Allergan, Inc, Irvine, CA) to strabismusin the early 1980s to include dystonic and non dystonic involuntary movementsas excessive muscle contraction accompanying strockle, demylination disease, tremor and cosmetic conditions.
BTX exerts its effect at the neuromuscular junction  inhibitingthe release of acetylcholine causing paralysis; there are three steps intoxinmediated paralysis (a)  irreversible binding to presynapticcholinergicnerve terminals, (b) internalization and (c) blocks the exocytosisof theneuro-transmitter  acetylcholine, thereby inhibiting musclecontraction.Toxin binding to both peripheral and central nerves is selectiveand saturable(1,2). Toxin inoculation can be easily performed in superficialmuscle, onthe other hand whenever dealing with deep muscle is usuallyperformed by EMGguidance.
The aim of our study was to evaluate the possibility of  CT asa unique step in diagnosis and treatment.


Materials and Methods


In the current study 15  patientswith piriformis syndrome whosuffered pain in the buttock , hip and referralpain down the posteriorthigh, calf and ankle because of the contracture ofpiriformis and dueto strain on the sciatic nerve, were treated by local intramuscular injectionof botulinic toxin type A under CT guidance. A control was doneafter 30days. The patients  studied were 9 women and 6 men;  theiragesranged from 32 to 54 years (mean age 43 years); the right pyriformismusclewas affected in 8 patients and the left one in 7. A woman had hip prosthesisin the affected side.
  All patients were examined neurophysiologically by Electromiography which was performed before treatment evaluating vastus lateralis of quadriceps, anterior tibialis, and gastrocnemius in the simptomatic side.
Neurography of Tibial and Peroneal nerves with evaluation of amplitude,conduction velocity and F wave was performed. H reflex from soleus wasevaluated  at basal condition and 1 month after the treatment. Patients selectioncriteria for intramuscular BTX injection was: constant pain tobuttock, hipand refferal pain down the posterior aspect of the thigh;failed medical andphysical treatment, negative  X ray and MRI ofthe spine and hip
All  examinations were performed with a CT unit (Tomoscan SR 7000-Philips)  with patients   in prone position on radiologictable (fig.1), scanning of the pelvis was acquired at 120KVP and 350 mas;FOV was 350 mm slice thickness  and index was 5 mmfrom the pelvis tothe greater trocanther;  a 20 Gneedle, 10 cm length,was used for  injection. A pre-test with an injectionof localanaesthetic( 5cc of Lidocaine2%) was performed to evaluate the reliefof pain. Before andafter the anaesthetictest, three clinical manouverwere performed to evaluatethe pain.  ALasegue’s  sign ( hipflexed at 90° and intrarotated)was doneto test the  pain’sdegree,Freiberg’s manouverof forcefulinternal rotation of the extendedthighis thought to elicit pain bystreching the irritated piriformis;thismanouver produces pressureon sciaticnerve  at the sacrospinousligament.Pace’s manouverelicits painwith the patient seated and abductingthelegs against the resistenceof theexaminer’s hands. These manouverswere  followed by an intramuscolarinjection of Botox (200 U/1.0 mlin saline) (fig.2a).  Direction anddepth of needle insertion wascalculated accordingto the side and depth ofthe affected pyriformis.Muscle's depth is medianly5-6 cm. Intra muscularposition of the needlewas confirmed by CT before anyinjection(fig.2b). Atthe end of procedure,few scan covering all the piriformismuscle were acquiredto avaluate itsmorphology and density.




Electromiography did not show signsof denervative process. Interferentialpattern was achieved in all the examinedmuscles, the Motor Unit ActionPotentials being in the range of amplitudeand duration for each muscle.H reflex was symmetric with a mean latency insymptomatic side of 29.4+/- 1.4 versus 29.3 +/- 1.5 after 1 month. F wavefor the tibial nervewas 46.7+/- 3.5 versus 46.5 +/- 3.7 and for peronealnerve 48.7 +/- 2.7versus48.9 +/- 2.9.
CT aspect of the affected side of pirifomis muscle is often hypotrophicrespect to the other side before local injection of botox. After injectionwe could see the muscle greater than the other .
Successful Toxin injection within pyriformis muscle was achieved inall the 15 patients with CT guidance.
In 12 cases  relief of symptoms was obtained after 5-7 days.
In the other 3 patients  there was insufficient relief of pain.We believe that pain was due to multisymptomatic syndrome(7,8). No bilateralcases were encountered.
No pain grading system was used in this study, our judge was basedif there was response or not.




Anatomically PM arises from the pelvicsurface of the sacrum, exits the pelvis through the greater sciaticforamen andinserts on theupper border of the greater trochanter by meansof a roundedtendon.Themuscle is innervated by branches from L5-S1 and S2nerve roots.The piriformismuscle is functionally and external rotaror ofthe hip jointwhen the thighis extended and an abductor of the hip jointwhen the thighisflexed.
Piriformis syndrome is a form of myofascial pain syndrome caused bycontracture of piriformis muscle and characterized by pain in the buttock,hip and refferal pain down the the posterior thigh. In the        observed patients  PMS causes were due to spasms, trauma and post-surgery.                
Traditional methods for relief of this myofascial pain include slowstrech exercise, massage, heat, ultrasound and muscle relaxant medication.
The introduction of botulinic toxin type A  allowed  a newtherapeutic approach in such pathological condition.There is typicallya 24-72 hours delay between administration of toxin and onset of clinicaleffect (2). Local intramuscular injection of botulinic toxin has been demonstratedto provide effective and safe managements of disorders characterized byinappropriate muscle spasm. Botox can inhibit muscle contraction for longperiod (5-6 months) producing greater relief by selective weakening painfulmuscle with mildly reportedside effects.  Our patients are belowsx months from toxin’s inoculation, and its effect is still during. CTguidance for toxin inoculation in the affected muscle, especially whendealing with deep muscles is highly affidable andin our experience givesbetter results than the other way.   Ct  imaging canbe diagnostic in the evaluation of patients with suspectedPMS;CT permits  also a morpholofgic evaluation of affected muscle,whichcouldbe ipo or ipertrophic(6) (fig.3). MR does not seem to offer abettervisualization.




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Volumetric asimmetry of pyriformis muscle with right’swithright’s hypertrophy


Right Pyriformis muscle infiltration

post inflitraz

After inoculation,pyriformis muscle appearsstretched;                                
is well evident the toxin solution inside.