A 33 year-old right-handed man with B-cell ALL (on active chemotherapy with blinotumumab, ponatinib, and intrathecal chemotherapy with methotrexate and cytarabine) had PICC insertion with multiple attempts, with immediate swelling and bruising of right arm. Four days later he noted right hand/forearm weakness. At our institution 3 months later, he had atrophy of right thenar muscle group, weakness in flexor pollicis 0/5, APB 0/5, and FDPII 2/5, and pronator teres 4+/5. He was unable to make the OK-sign with right hand.  Sensation was reduced in digits 1-3 and radial snuffbox; reflexes 2+ bilaterally. EMG confirmed severe, ongoing right median neuropathy proximal to the takeoff to pronator teres, and mild right brachial plexopathy.

Five months after PICC insertion, MRI showed injury of proximal median nerve and edema in FPL and FDP. Two months later MRI showed T2-hyperintensity and thickening of lateral C6 nerve root and brachial plexus. Leukemic infiltration was considered less likely. Lumbar puncture performed, with normal CSF findings.