Abstract / Summary
Abstract Parsonage–Turner syndrome (neuralgic amyotrophy) typically begins with severe shoulder pain, followed by patchy upper limb weakness. In an estimated 4–10% of cases pain is absent, making the diagnosis easy to miss. We describe a man in his late twenties who woke to find he could not lift his left arm beyond 15 degrees of abduction. Examination showed weakness across the left brachial plexus territory, maximal in the deltoid at MRC 2/5, with serratus anterior, supraspinatus, infraspinatus, biceps, brachioradialis and triceps at 3/5, scapular winging on resisted forward push, and preserved grip. He had tingling over the left shoulder but no pain and no sensory loss; a viral illness had resolved one week earlier. Deep tendon reflexes were absent in the left upper limb. MRI of the brain, cervical spine, and brachial plexus (day 1) and nerve conduction studies (day 2) were reported as normal. Repeat brachial plexus MRI on day 3 showed STIR hyperintensity in the left-sided trunks and divisions, supporting a diagnosis of probable neuralgic amyotrophy. Needle electromyography was not performed during the acute illness, so the diagnosis was not established electrophysiologically. Intravenous methylprednisolone and physiotherapy were given, and power was MRC 5/5 throughout the limb at four weeks. At 20 months he remained asymptomatic, but the left axillary compound muscle action potential amplitude was approximately half that of the contralateral side, having been the larger of the two on day two. Painless neuralgic amyotrophy is under-recognised, and normal early investigations do not exclude it. Repeat imaging provided supportive evidence in this patient, though the two examinations were not acquired with identical parameters and a single case cannot establish how often this occurs.