Isolated Infraspinatus Wasting: A Case Report

Case Diagnosis: A 57-year-old woman with progressive shoulder pain and weakness due to focal impingement of the suprascapular nerve at the suprascapular notch.

Case Description or Program Description: A middle-aged woman presented to an outpatient sports medicine clinic with a 10-month history of chronic, atraumatic progressive left shoulder weakness. She was initially diagnosed with rotator cuff tendinopathy, but failed appropriate conservative management, including physical therapy. A subacromial bursa corticosteroid injection provided some improvement in pain, however, symptoms recurred. Examination revealed decreased left shoulder active range of motion with pain during abduction and external rotation. Serial examinations identified progressive weakness and atrophy of the left infraspinatus muscle.

Setting: Outpatient Sports Medicine Clinic

Assessment/Results: Plain radiographs of the left shoulder demonstrated mild glenohumeral degenerative change. Magnetic resonance imaging of the left shoulder was notable for calcific tendonitis of the supraspinatus tendon. Due to progressive weakness and localized atrophy of the left infraspinatus, nerve conduction study/needle electromyography was performed and showed reduced amplitudes of both the left supraspinatus and infraspinatus at Erb’s point. Needle electromyography was significant for severe active denervation of the left infraspinatus with sparing of the supraspinatus. The patient was referred for neurosurgical evaluation and subsequently underwent left suprascapular nerve decompression at the suprascapular notch. Postoperatively, infraspinatus strength was graded at 3/5. With continued physical therapy, the patient regained nearly full strength and muscle bulk within 6 months.

Discussion (relevance): Suprascapular nerve entrapment, though well-documented, is a relatively rare condition, accounting for 1 to 2 percent of all cases of shoulder pain. Given its rarity, it can easily be overlooked in the differential diagnosis of shoulder discomfort.

Conclusions: Careful physical examination and multimodal diagnostic evaluation, including advanced imaging and electromyography, are crucial when evaluating shoulder pain and weakness unresponsive to conservative approaches.