An unusual cause of unilateral shoulder weakness: Parsonage–Turner syndrome—A case report

Abstract

Parsonage-Turner Syndrome (PTS) is characterized by an initial episode of intense pain followed by muscle weakness, atrophy, and sensory abnormalities within the peripheral nervous system. A painless variant known as Neuralgic Amyotrophy may present bilaterally (~30%) and exhibit recurrent patterns. While the upper brachial plexus is typically affected, PTS can also impact the lumbosacral plexus or manifest as an isolated peripheral mononeuropathy. The condition's origins remain unclear but appear to involve genetic predisposition, immunologic events, and mechanical factors. Approximately 30 to 70% of PTS cases are triggered by events like infection, vaccination, pregnancy, or surgery. Describing a case of a 21-year-old male, our outpatient clinic encountered prolonged acute shoulder pain and motor weakness, leading to a PTS diagnosis after a year of persistent symptoms. The patient complained of left-sided neck pain radiating to the deltoid muscle, axilla, and shoulder blade during the visit. Electrodiagnostic studies confirmed denervation limited to the left deltoid muscle, excluding cervical radiculopathy.