(Kiosk 3) A Case of the Missing Sensory Nerve: Superior Gluteal Nerve Mononeuropathy

Case Diagnosis: Superior gluteal nerve mononeuropathy

Case Description or Program Description: A 31 year old patient presented for electrodiagnostic evaluation of 3 years of low back pain radiating through the right posterolateral lower limb to the sole of the foot. Since a motor vehicle accident 3 years prior, the patient had constant, fluctuating pain with occasional numbness in the right foot, but no limb weakness. MRI showed mild diffuse disc bulges at L4-L5, L5-S1 without central or foraminal narrowing, but repeated epidural steroid injections offered no relief. Pain was relieved with stretching, exercise, lidocaine patches, and transcutaneous electrical nerve stimulation. On physical examination, the patient had significant tenderness of the right gluteus medius and right quadratus lumborum with limited left lateral bending and rotation. Reflexes were symmetric and strength was intact. Sensation to light touch was decreased in a small, localized patch at the proximal anterolateral thigh.

Setting: Electromyography laboratory

Assessment/Results: There were no abnormalities in nerve conduction studies of the sensory superficial peroneal nerve nor the motor peroneal and tibial nerves. Electromyography revealed motor unit potential changes in the superior gluteal nerve-innervated tensor fascia lata and gluteus medius.

Discussion (relevance): This case describes an example of superior gluteal nerve mononeuropathy based on electromyography findings with correlating sensory changes in a small patch at the proximal anterolateral thigh. Most texts do not discuss sensory innervation of this region by the superior gluteal nerve, but rather by proximal branches of the lateral femoral cutaneous nerve. However, a study revealed cutaneous penetrating branches through the tensor fascia lata and gluteus medius originating from the superior gluteal nerve. As in this case, superior gluteal nerve entrapments have been previously described to radiate down the posterior lower limb to the foot and cause tenderness in the gluteal muscles.

Conclusions: Despite omission from mainstream literature, the superior gluteal nerve has been shown to have cutaneous innervation at the proximal anterolateral thigh. Sensory changes in the superior gluteal nerve distribution may help distinguish superior gluteal nerve entrapment from other causes of radiating lower limb pain.