Piriformis Syndrome and Neuropathic Fibular Pain Caused by Anomalous Sciatic Anatomy

 

 

David S Younger

 

 

David S Younger, Department of Neurology, New York University Langone Medical Center, New York University School of Medicine, and the Global Institute of Public Health, New York University, New York, the United States

Correspondence to: David S Younger, MD, MPH, Department of Neurology, New York University Langone Medical Center, New York University School of Medicine, and the Global Institute of Public Health, New York University, New York, the United States

Email: david.younger@nyumc.org

Telephone: +1-212-213-3778           Fax: +1-212-213-3779        

Received: November 19, 2014         Revised: December 26, 2014

Accepted: January 30, 2014

Published online: February 2, 2015

 

ABSTRACT

A 57-year-old woman with piriformis syndrome and neuropathic fibular pain was found to have high branching of the common fibular nerve division of the sciatic nerve above a bifed piriformis muscle leading to entrapment neuroimaging studies. This was successfully treated with corticosteroid injection in the vicinity of the piriformis muscle and along the sciatic perineurial space under

 

© 2015 ACT. All rights reserved.

 

Key words: Piriformis Syndrome; Fibular; Sciatic

 

Younger DS. Piriformis Syndrome and Neuropathic Fibular Pain Caused by Anomalous Sciatic Anatomy. International Journal of Neurology Research 2015; 1(1): 18-19 Available from: URL: http://www.ghrnet.org/index.php/ijnr/article/view/927

 

INTRODUCTION

Sacro-iliac joint arthritis was a cause of sciatica at the turn of the last century[1]; however the piriformis muscle, which spans the joint, became synonymous with sciatica evoked by passive internal rotation, hip flexion and abduction maneuvers. Piriformis syndrome was ascribed to contact of the muscle with upper sacral nerves and the sciatic trunk as they transited the infrapiriformis foramen (IF)[2]. Sectioning a tight iliotibial band[3], piriformis myotomy and fascial band releases[4], and physiotherapy have all been advocated as effective modes of therapy. Although over-diagnosed[5], there are subsets of affected patients with anomalous anatomy.

 

CASE REPORT

A 57-year-old woman noted left sciatica in 2006 followed lateral left calf, foot and ankle hyperalgesia and allodynia that was treated with opiod drugs, local injections into the superficial fibular sensory nerve and surgical repair of peroneal tendinopathy but without benefit. On neurological examination in June 2014 there was minimal extensor foot weakness but marked hyperesthesia along the left lateral calf and dorsum of the foot, without absent ankle reflex or left sciatic notch palpation tenderness. The right leg and arms were normal. There were no serological abnormalities suggestive of an underlying autoimmune, infectious or inflammatory disorder. Electrodiagnostic studies were consistent with left common fibular neuropathy involving the deep and superficial divisions with chronic axonal features. Non-contrast magnetic resonance neurography (MRN) of the pelvis showed a bifid left piriformis muscle with an intramuscular course of the common fibular nerve division that was deflected by the inferior piriformis muscle (Figure 1) as well as increased signal intensity along the nerve at the infrapiriformis foramen. She underwent ultrasound-guided injection of 1.5 cc betamethasone and 1.5 cc 0.5% ropivacaine in the vicinity of the piriformis muscle and along the sciatic perineurial space followed by improved pain.

 

DISCUSSION

Treatable unilateral sciatica and neuropathic pain has been causally associated with anomalous anatomy of the piriformis muscle and sciatic nerve. A study of 168 cadaveric dissections showed division of the sciatic trunk above the IF into a fibular component that pierced the piriformis muscle leading to possible entrapment, while the tibial component exited normally[6]. Chen[7] noted sciatic nerve entrapment through a bifed piriformis muscle at surgical exploration for progressive sciatic neuropathy in one patient who improved with surgical resection of the lower muscle belly.  There is a rat model of sciatic mononeuropathy due to experimental chronic constriction injury in which morphological and functional nerve changes were associated with hyperalgesia and allodynia similar to the distal fibular neuropathic complaints in the present patient[8]. 

 

CONFLICT OF INTERESTS

The Author has no conflicts of interest to declare.

 

REFERENCES

1         Albee FH. A study of the anatomy and clinical importance of the sacro-iliac joint. JAMA 1909; 4: 1273-1275

2         Yoeman, W. The relation of arthritis of the sacroiliac joint to sciatica. Lancet 1928; 2: 1119-1122

3         Ober, Frank R. Back strain and sciatica. JAMA 1935; 104: 1580-1583

4         Freiberg, AH. Sciatic pain and its relief by operations on the muscle and fascia. Arch Surg 1937: 104; 337-350

5         Stewart JD. The piriformis syndrome is overdiagnosed. Muscle Nerve 2003; 28: 644-646

6         Lee CS, Tsai TL. The relationship of the sciatic nerve to the piriformis muscle. Forosan Med Assoc 1974; 73: 75-80

7         Chen W-S. Bipartite piriformis muscle: an unusual cause of sciatic nerve entrapment. Pain 1994; 5: 269-272

8         Lindenlaub T, Sommer C. Epidermal innervation density after partial sciatic nerve lesion and pain-related behavior in the rat. Acta Neuropathol 2002; 104: 137-143

 

Peer reviewer: Janny Sun, Emeritus Professor, Hong Kong, Editor-In-Chief of International Journal of Neurology Research, ACT Publishing Group Limited Company.

 

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