A Novel Report of Nivolumab-Induced Parsonage-Turner Syndrome Associated with Hourglass-like Constriction of the Anterior Interosseous Nerve (P2.437)

Objective: NA Background: Parsonage-Turner Syndrome (PTS), also known as neuralgic amyotrophy, is an inflammatory peripheral nerve disorder, classically presenting with severe pain followed by weakness in one or more nerve territories, often including the anterior interosseous nerve (AIN). PTS is often associated with an antecedent event such as infection, surgery, vaccination, or medication. Surgical and high resolution nerve ultrasound (HRUS) studies have demonstrated focal, hourglass-like constriction in some cases. To our knowledge, this is the first report of PTS occurring in association with nivolumab, as well as the first report of hourglasslike HRUS findings in chemotherapyassociated PTS. Design/Methods: NA Case Report: A 71-year-old male with lung adenocarcinoma presented one week following cycle 2 of nivolumab therapy with severe acute bilateral proximal upper extremity pain with subsequent recognition of hand weakness and numbness. The patient's pain improved over 1 week, but he was left with residual weakness of the right hand, including marked difficulty grasping objects between his index finger and thumb. Physical exam revealed 1/5 strength of the right flexor pollicis longus and right flexor digitorum profundus, localizing to the right AIN. MRI of brachial plexus was unremarkable. Ultrasound of the right median nerve demonstrated an enlarged hypoechoic fascicle branching off the median nerve at the antecubital fossa consistent with an enlarged AIN. In addition to segmental enlargement, an area of focal constriction was seen in long-axis views, consistent with an hourglass-like constriction. EMG studies were consistent with an anterior interosseous mononeuropathy. Conclusions: The authors report the first known case of neuralgic amyotrophy due to nivolumab therapy, although this phenomenon is seen in the setting of other neurotoxic chemotherapeutic agents. This case is also notable for the ultrasonographic appearance of an hourglass-like constriction, a finding increasingly reported in neuralgic amyotrophy, particularly involving the AIN, although as of yet not in this clinical setting.