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Ganglia can compress the adjacent structures and in the shoulder they can cause suprascapular neuropathy.1,2 We report an unusual case of a ganglion cyst that caused entrapment neuropathy of the inferior branch of the suprascapular nerve mimicking cervical disk disease.
A 39 year old man presented to our physical medicine and rehabilitation outpatient clinic with neck and left shoulder pain together with weakness of his left arm. His complaints were of nine months’ duration. A cervical spinal magnetic resonance imaging (MRI) examination showed diffuse bulging of C4-5 and C5-6 disks and flattening of cervical lordosis. Physical examination showed a loss of muscle strength at external rotation and significant atrophy of the infraspinatus muscle. Initial electromyography and nerve conduction studies (EMG/NCS) restricted to the supraspinatus muscle were normal. Later studies inclusive of the inferior branch of the suprascapular nerve and the infraspinatus muscle, however, showed prolonged distal latency (12 msec) and low amplitude (0.2 mV) responses. Moreover, needle-EMG displayed severe subacute neurogenic involvement as well as atrophy of the left infraspinatus muscle and partial denervation findings. The EMG/NCS findings for other muscles and nerves were normal. Because findings suggested entrapment of the inferior branch of the left suprascapular nerve at the level of the spinoglenoid notch, a diagnostic injection of 5 ml lidocaine 2% was made at this location, whereupon the pain of the patient was relieved.
MRI of the left shoulder showed a round cystic mass about 2 cm in diameter and consistent with ganglion posterosuperior to the glenoid portion of the scapula (fig 1). The patient refused surgery upon relief of his pain. Local injections of lidocaine with 40 mg methylprednisolone acetate were made three times, each with an interval of three weeks. In addition, electric stimulation and isometric and isotonic strengthening exercises were given to the infraspinatus muscle. Follow up MRI at two months after the first injection showed no regression of the cystic mass. Persistence of the symptoms three months thereafter and heavy workload of the patient (which he could not dismiss) led to open decompressive surgery with posterior approach. All symptoms of the patient were relieved after the operation and MRI at three months after surgery showed no residual or recurrent cystic mass.
The diagnosis of suprascapular nerve entrapment is based on clinical history and physical examination supplemented with EMG/NCS.3–6 Patients typically present with longstanding, deep, diffuse posterolateral shoulder pain, which may radiate to the neck, arm, or upper chest wall.3 In our case, the diagnosis was delayed because of this pain distribution. This sensation of pain is probably referred from the sensory articular branches to the glenohumeral and acromioclavicular joints.2 On physical examination, there is usually weakness of external rotation. Wasting of the infraspinatus would be present in chronic conditions.3 Pain relief after an injection of lidocaine into the area of entrapment can be used as a confirmatory diagnostic sign.7 EMG/NCS should be performed to confirm the diagnosis of entrapment neuropathy of the suprascapular nerve.2,6 Nevertheless, such an evaluation should not be restricted to the supraspinatus and should encompass the infraspinatus. Assessment of the infraspinatus, along with supraspinatus, can avoid the failure of diagnosing the compression at the spinoglenoid notch, as documented in our case.
Suprascapular nerve entrapment in the suprascapular notch, especially in the spinoglenoid notch, is a rare entity that must be considered in the differential diagnosis of radicular pain, as well as that of shoulder discomfort.7 Radiological findings of cervical disk degeneration are widely encountered, increasing with age.8 Extensive use of MRI results in the frequent diagnosis of cervical disk disease. It should be borne in mind, however, that symptoms of a patient need not be wholly attributable to the presence of cervical disk disease, which might be associated with another condition causing similar symptoms, as in our patient.
In conclusion, extensive use of EMG/NCS should be made in patients with shoulder pain with associated atrophy. Ganglion cysts at the spinoglenoid notch should be included in the differential diagnosis of patients presenting with neck and shoulder pain and weakness.