An MRI evaluation of changes in piriformis muscle morphology induced by botulinum toxin injections in the treatment of piriformis syndrome.
OBJECTIVE
Botulinum toxin (BT) injection is a new treatment for piriformis syndrome (PS). The main purpose of our study was to use MRI to evaluate changes in piriformis muscle morphology after treatment with BT injections.


METHODS
Twenty patients presenting with PS who had undergone an MRI were included retrospectively: 12 patients treated with BT injections and eight untreated patients. The following parameters were assessed and compared to a normal contralateral muscle: maximum thickness, volume, and Goutallier's classification grade of fatty infiltration of the piriformis and internal obturator muscles. Pain was assessed through a visual analogue scale (VAS).


RESULTS
The untreated patients had no significant difference in the volume (P=1.0) or thickness of the piriformis muscle (P=0.61). The treated patients showed a significant reduction in the thickness (-4.2mm; P<0.001) and volume (-74.4mm(3); P<0.001) and an increase in the fatty infiltration (P<0.001) of the piriformis muscle treated by BT injection. Muscular atrophy was correlated with the number of BT injections and with the time until an MRI was performed. There was also significant pain relief after BT treatment.


CONCLUSIONS
BT leads to atrophy and fatty degeneration of the piriformis muscle that can be quantified by MRI and these factors explain why BT injections are effective in the treatment of PS.
Department of Osteoarticular Imaging, Besançon Regional University Hospital, hôpital Jean-Minjoz, 3, boulevard Alexandre-Fleming, 25030 Besançon cedex, France.
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M
Al-Al-Shaikh
Department for Neuromuscular Disease and Exploration, Besançon Regional University Hospital, 3, boulevard Alexandre-Fleming, 25030, Besançon cedex, France; Laboratory I4S, EA4268 IFR133, University of Franche-Comté, 25000 Besançon, France.
F
F
Michel
Department of Physical Medicine and Rehabilitation, Besançon Regional University Hospital, 3, boulevard Alexandre-Fleming, 25030 Besançon cedex, France; Anatomy Laboratory, University of Franche-Comté, 25000 Besançon, France.
B
B
Parratte
Department of Osteoarticular Imaging, Besançon Regional University Hospital, hôpital Jean-Minjoz, 3, boulevard Alexandre-Fleming, 25030 Besançon cedex, France; Laboratory I4S, EA4268 IFR133, University of Franche-Comté, 25000 Besançon, France.
B
B
Kastler
Clinical Investigation Centre, Besançon Regional University Hospital, 3, boulevard Alexandre-Fleming, 25030 Besançon cedex, France.
C
C
Vidal
Department of Osteoarticular Imaging, Besançon Regional University Hospital, hôpital Jean-Minjoz, 3, boulevard Alexandre-Fleming, 25030 Besançon cedex, France; Laboratory I4S, EA4268 IFR133, University of Franche-Comté, 25000 Besançon, France. Electronic address: saubry@chu-besancon.fr.
S
S
Aubry
D000328:Adult; D000368:Aged; D001905:Botulinum Toxins / Q000008:administration & dosage / Q000494:pharmacology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015552:Injections, Intralesional; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology*; D055958:Piriformis Muscle Syndrome / Q000188:drug therapy*; D012189:Retrospective Studies
D001905:Botulinum Toxins
Botulinum toxin; MRI; Obturator internus muscle; Piriformis muscle; Piriformis syndrome