(Kiosk 1) An Unusual Case of Wrist Drop in a Traumatic Brain Injury Patient: A Case Report

Case Diagnosis: Wrist drop due to radial nerve mononeuropathy with superimposed heterotopic ossification involving the interosseous syndesmosis of the forearm.

Case Description or Program Description: A 25 year old left handed male with no prior medical history presented to inpatient rehabilitation (IPR) following a motor vehicle collision with resulting severe traumatic brain injury and polytrauma notable for left radius and ulnar fractures that were surgically repaired. His IPR course was complicated by worsening left forearm and wrist weakness. On exam, he was noted to have intact proximal left arm strength, but 2/5 strength with left wrist extension, finger extension, and forearm pronation and supination. Wrist flexion, finger flexion, and finger abduction were intact. He also had reduced sensation over his dorsal left hand.

Setting: Inpatient rehabilitation hospital

Assessment/Results: X-ray of the left forearm demonstrated healing both bone fracture status post open reduction internal fixation and heterotopic ossification (HO) with intraosseous bridging. He followed up with his orthopedic surgeon, who noted significant heterotopic ossification with concern for posterior interosseous nerve (PIN) palsy. Electrodiagnostic testing and CT were ordered. The CT again demonstrated bridging heterotopic bone formation across the interosseous syndesmosis. Electrodiagnostic testing demonstrated a severe, acute-on-chronic left radial mononeuropathy that localized just proximal to the elbow.

Discussion (relevance): The differential diagnosis for wrist drop includes PIN or radial nerve mononeuropathies, brachial plexopathy, and radiculopathy. Given the location of the HO and anatomic course of the PIN, PIN mononeuropathy was initially thought to be the leading differential diagnosis of this patient’s weakness. The physical exam findings were confounded by HO of the interosseous syndesmosis of the forearm, causing restricted supination and pronation.

Conclusions: Wrist drop caused by radial nerve mononeuropathy can be differentiated from other etiologies by physical exam and electrodiagnostic findings.