Poster 42: Electrodiagnosis of suprascapular nerve entrapment with negative shoulder magnetic resonance imaging: a report of 3 cases

Abstract

Setting: Private practice. Patients: 3 adults with painful shoulders. Case Description: All 3 patients presented with chronic posterior shoulder pain. One complained of pain radiating distally past the shoulder, but that patient also had a diagnosis of a cervical radiculopathy. Another patient was also diagnosed with a cervical myelopathy. All 3 had weakness and atrophy in the supraspinatus and/or infraspinatus. All 3 patients had magnetic resonance imaging (MRI), which did not show any lesion of the suprascapular nerve. However, 2 had partial supraspinatus tears. Electrodiagnostically, 2 had delayed latencies of the compound motor action potential (CMAP): one to the infraspinatus and the other to the supraspinatus. Electomyographic findings in all 3 patients showed increased spontaneous potentials in the form of fibrillations and positive waves with reduced recruitment. Assessment/Results: Postoperatively, 2 patients had immediate reduction or elimination in pain and improved range of motion. The third patient was scheduled for suprascapular nerve decompression. Discussion: Suprascapular nerve injuries result from trauma, overuse, or a mass lesion. Common symptoms are posterior shoulder pain, weakness, and atrophy in the supraspinatus or infraspinatus. Injury at the suprascapular notch will cause abnormal nerve conduction studies (NCSs) or electomyographic findings at the supraspinatus and infraspinatus. The spinoglenoid notch is the distal site of injury and abnormalities are found only at the infraspinatus. MRI is useful in evaluating for ganglion cysts or denervation of muscle; but these abnormalities were not identified in these case reports. Conclusion: Suprascapular nerve injuries are uncommon, but should be strongly considered in patients with significant pain and weakness of the shoulder. False negative MRIs are seen commonly. Electomyography and NCS are specific and sensitive to help localize the site of injury for surgical decompression.