The hallmarks of Parsonage-Turner syndrome, also known as acute brachial neuritis, include the sudden onset of severe atraumatic pain in the shoulder
girdle and the spontaneous resolution of the pain within 1 to 3 weeks. Persistent muscle weakness is often noted after the subsidence of the acute symptoms. The cause of the entity is still unclear, but viral and immunological etiologies have been implicated [29,30]. There is a wide age range at presentation, and the condition is much more common in males [31,32].
Initially it was believed that the long thoracic nerve is the most common nerve to be involved in Parsonage-Turner syndrome ; however, later reports have indicated a higher incidence of isolated suprascapular nerve disease . Other nerves such as the axillary, radial and phrenic nerves , as well as the entire brachial plexus , may also be affected. Bilateral involvement is common and can be seen in up to one third of patients . Abnormal
Fig. 5. Axillary neuropathy and labral tear following anterior shoulder dislocation. Axial proton density-weighted image shows atrophic changes of the teres minor muscle (TMi) associated with a nondisplaced tear of the anteroinferior labrum (arrow).
electromyographic pattern with fibrillation potentials and positive waves is characteristically encountered in Parsonage-Turner syndrome .
The clinical symptoms and signs of Parsonage-Turner syndrome can mimic a wide range of disease entities, such as rotator cuff disease, cervical radiculop-athy, spinal cord tumor, and peripheral nerve compression. Differentiation of the entity from compressive neuropathy of the suprascapular nerve can be particularly confusing. Useful features in distinguishing Parsonage-Turner syndrome from suprascapular nerve entrapment include the more insidious onset of pain and lack of spontaneous resolution of symptoms noted in the latter entity. MRI detection of paralabral ganglions or other impinging mass lesions within the suprascapular notch is also supportive of suprascapular nerve entrapment . MRI can also be useful in excluding other disease entities such as rotator cuff tear, which can clinically mimic Parsonage-Turner syndrome.
Diffuse increased signal intensity on fluid-sensitive sequences consistent with interstitial muscle denervation edema can be seen on MR imaging during the acute stage of Parsonage-Turner syndrome . The supraspinatus and infra-spinatus muscles are the most commonly affected muscles, but the deltoid can also be involved (Fig. 6A). Muscle atrophy manifested by decreased muscle bulk may be visualized later on (Fig. 6B).
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