Journal ofNeurology, Neurosurgery, and Psychiatry 1991;54:241-243 241 Suprascapular nerve lesions at the spinoglenoid J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.54.3.241 on 1 March 1991. Downloaded from notch: report of three cases and review of the literature Jay A Liveson, Michael J Bronson, Michael A Pollack Abstract of root involvement (cervical pain, and change Lesions of the suprascapular nerve can from Valsalva's manoeuvre). His past medical occur at the supraspinatus notch (SSN) history was negative. On physical examination or at the spinoglenoid notch (SGN). Elec- cranial nerves were normal. No weakness was tromyographic (EMG), evaluation of the detected on careful manual muscle examin- infraspinatus, and especially the supra- ation. Sensation was intact. Deep tendon spinatus muscles distinguishes SGN reflexes were active and symmetrical with no from SSN lesions. Three cases of SGN pathological reflexes. There was no Homer's lesions, which are more common than sign. SSN lesions, are presented. The patient gave up weight lifting and started a programme of physiotherapy. His shoulder ache resolved rapidly, but his muscle Entrapment of the suprascapular nerve at the bulk did not return to normal for another 12 suprascapular notch (SSN) was first described months. He reported completely normal func- in 1963 by Kopell and Thompson.' No alter- tion. native entrapment site was recognised until 1981 when the first case of spinoglenoid notch Case 2 (SGN) entrapmnt was described by Ganzhorn A 22 year old right handed male was skeet et al.2 Since then nine additional cases of SGN shooting, a month before his examination. He lesions have been published.34 It is important held the rifle so that the recoil was absorbed by to distinguish between the SSN and the SGN the right shoulder. The following day, he Saul R Korey Department of lesions (fig 1) to avoid surgery to the wrong found that he was unable to lift the right Neurology, Albert region. This may be the cause of occasional shoulder. This gradually subsided but his Einstein College of surgical failure reported before the SGN right scapula appeared to be losing bulk. He Medicine, Bronx, NY, USA lesion was recognised.9 We present a report of did not complain of numbness or radicular J A Liveson three additional cases of SGN lesions and a symptoms. His past medical history was M J Bronson review of the literature to define the SGN negative. On physical examination atrophy M A Pollack syndrome. was evident in the region of the right infra- Correspondence to: spinatus with an area of tenderness below the Dr Liveson, scapular spine. There was no weakness on http://jnnp.bmj.com/ 159 East 74 Street, New Case 1 York, NY 10021, USA A 22 year old right handed weight lifter noted manual muscle examination, and sensation Received 31 January 1990 right shoulder ache which remained un- was intact. Deep tendon reflexes were active and in final revised form and symmetrical with flexor responses. 5 July 1990. changed during the previous six months. He plantar Accepted 23 July 1990 did not complain of numbness, or symptoms Cranial nerves were normal with no Homer's sign. Figure I Suprascapular The patient was treated conservatively. His nerve entrapments. From strength and scapular muscle bulk increased Liveson JA. Peripheral slowly. After 30 months they were completely on September 26, 2021 by guest. Protected copyright. neurology: case studies in electrodiagnosis, 2nd ed. normal. Philadelphia: FA Davis, 1991 (In press). Case 3 A 25 year old right handed minor league baseball pitcher was alerted by teammates to right scapular atrophy two months before being examined. He was still able to pitch, and denied numbness, and cervical symptoms. 1 -suprascapular nerve There was no precipitating event. His past 2-branch to medical history was negative. On physical supraspinatus examination cranial nerves were normal with 3-branches to joint capsule no Horner's sign. Atrophy was evident in the 4-branch to right infraspinatus region and external rota- infraspinatus tion of the right humerus was weak. No other 5-supraspinatus notch (SSN) motor or sensory deficit was present. Deep 6-scapular spine tendon reflexes were active and symmetrical 7-spinoglenoid notch and plantar responses were flexor. (SGN) 8-glenoid rim After a temporary leave, the patient 9-coracoid process resumed his normal pitching routine finding 1 0-joint capsule that he was able to function completely nor- 242 Liveson, Bronson, Pollack J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.54.3.241 on 1 March 1991. Downloaded from mally. When he was re-examined nine months using a surface electrode, as a needle electrode later, he did not complain of any symptoms. records from a limited field. In addition, Although some residual atrophy was still because of the variation in normal values apparent, the strength of his infraspinatus was (probably reflecting the range ofthe overlaying found to be normal. superficial muscle thickness in athletic shoul- ders), a normal control value would best be Electrodiagnostic findings measured in the asymptomatic arm of the same Electrodiagnostic studies in all cases demon- patient. strated isolated denervation in the infra- In case 3 there is a prolonged latency which spinatus consisting of fibrillation potentials, suggests a conduction abnormality. This can positive sharp waves and single unit recruit- occur in a focal lesion of the myelin or in an ment of normal motor unit potentials (MUPs). axonal lesion during the early reparative stage Extensive electromyography (EMG) estab- (as may low amplitude MUPs) because of loss lished no other abnormalities (and included ofthe faster conducting fibres and regeneration examining the following muscles in all cases: ofimmature fibres which initially conduct more supraspinatus, mid to low cervical paraspinal slowly." muscles, serratus anterior, deltoid, biceps The key muscle to examine to distinguish brachii, triceps brachii, brachioradialis, flexor between a lesion at the SSN and the SGN is the carpi radialis; and the following muscles in supraspinatus. If this is involved, the lesion most cases: trapezius, rhomboids, extensor cannot be at the SGN. Sparing of the supra- carpi radialis, flexor pollicis longus, first dorsal spinatus, in contrast to marked infraspinatus interosseous, abductor pollicis brevis). MUPs involvement, places the lesion at the SGN. did not suggest myopathy (that is, low- We reviewed all the SGN cases, including amplitude, short duration MUPs were not the 10 that were previously reported.28 In all present diffusely), and screening of peripheral cases, there was a relationship with strenuous nerves for a diffuse condition was negative. exercise. It occurred primarily in males bet- The compound muscle action potentials ween the ages of 18 and 41, although the oldest (CMAPs) to the denervated infraspinatus patient was 79. Pain was not a major complaint muscles were also abnormal (standard pro- in most cases. Weakness may not be a major cedures used'0 consisted of symmetrically feature, even on manual muscle testing. There placed surface electrodes to monitor the res- was an insidious onset with the patient often ponses on Erb's point stimulation). In two unaware until an observer commented on the cases surface electrodes were used and the atrophy. CMAP amplitude was found to be significantly The absence ofweakness deserves comment. low in comparison with the asymptomatic side It is possible that external rotation is omitted (38% and 50%), but the latency was normal during the manual muscle examination. It is and symmetrical (2-8 to 3-1 ms). In the third also possible, however, for a deficit to be case, needle electrode monitoring was used compensated by synergistic muscles. A similar (precluding reliable measurement of the situation has been documented in cases of CMAP amplitude), but the latency was pro- axillary nerve lesions where synergistic mus- longed (14-8 ms compared with 3 2 ms on the cles have been seen to substitute effectively for asymptomatic side). atrophic deltoid muscles.'2'14 Perhaps substitu- http://jnnp.bmj.com/ tion is occurring here where the patients are all Discussion athletes in excellent physical condition. These three patients were athletic males The previously reported 31 cases of SSN between the ages of22 and 25 years. An isolated lesions were reviewed.9 15127 In 21 there was event (skeet shooting) preceded the onset in information indicating that the supraspinatus one. The other deficits developed insidiously was also involved, placing the lesion at the with a shoulder ache occurring in one. In only SSN. In ten cases, however, this was one case was weakness demonstrated on careful unclear9' 15, 22,25, 26 as it is impossible to tell on September 26, 2021 by guest. Protected copyright. manual muscle examination. whether EMG examination was performed on The clinical differential diagnosis ofshoulder the supraspinatus muscle. In one case, ironic- weakness (before the focality is demonstrated) ally, "the patient was referred for EMG evalua- includes the more common C5, C6 tion of the right infraspinatus."26 Another radiculopathy, a myopathy (such as patient reported in 1975 with external rotation polymyositis), a Parsonage-Turner syndrome weakness had a decompression ofthe SSN only (brachial plexitis), and rotator cuff injury. The and did not improve.9 This may well be a case latter two were unsupported by history. All but of SGN entrapment. Thus before there was an the last were unsupported by electrodiagnostic awareness of the alternative localisation to the studies. SGN, some of the reported cases of SSN The lesion involved the innervation of the lesions may have been erroneously localised. infraspinatus muscle only, consistent with a The true frequency of SGN lesions is probably lesion at the SGN. These abnormalities were higher than is apparent from the literature, as primarily axonal in two cases-denervation on suggested by our experience.