Acute Ulnar Neuropathy at the Elbow: Clinical, Electrodiagnostic, and Ultrasonographic Findings

Background/Objectives: Ulnar nerve neuropathy at the elbow (UNE) is the second most common focal neuropathy of the upper extremity and often results from entrapment of the ulnar nerve as it traverses the elbow with insidious onset and gradual progression. This study describes the clinical, electrodiagnostic (EDX), and ultrasound (US) findings in a cohort of patients presenting with acute UNE. Methods: This is a review of 103 patients with clinical features of UNE with acute onset who underwent EDX and US studies over a 25-year period (2010–2026) at our Neurodiagnostic Center. Results: Of the 103 patients with acute UNE, all experienced paresthesia in the ulnar nerve distribution. A total of 27 (26.2%) patients had elbow pain, and 99 (96.1%) had decreased pinprick sensation in the ulnar nerve distribution. Weakness of the following muscles was detected: abductor digiti minimi (ADM) (94 [91.3%]), FDI (first dorsal interosseous) (91 [88.3%]), and FDPu (flexor digitorum profundus—ulnar) (76 [73.8%]). Most patients had a clinical grade of 3 (severe: sensory and motor abnormalities as well as atrophy of the FDI and ADM muscles) (93 [90.3%]). Perioperative injuries were the most common etiology of acute UNE, consisting of 65 (63.1%) patients. The perioperative injury was noted after surgical procedures at varied locations, most frequently at the shoulder in 23 (35.4%) followed by coronary artery bypass in 9 (13.8%) and knee joint surgery in 8 (12.3%). Non-iatrogenic injuries affected 11 (10.7%) patients. The US study revealed cysts and tumors such as a Schwannoma in 14/76 (18.4%) patients. Focal demyelination was observed by EDX studies in 95 (92.2%) patients, and a conduction block was detected in 24 (23.3%). Motor and sensory axonal involvement was identified in 81 (78.6%) and 86 (83.5%) patients, respectively. Of the 76 patients who underwent an US study, 68 (90.6%) had an increase in the cross-sectional area of the ulnar nerve and 51 (68.0%) had a hypoechoic ulnar nerve at the elbow. Conclusions: In this study, the most common cause of acute UNE was periprocedural injury, most frequently following shoulder surgery. Acute UNE may also occur without a history of antecedent trauma or a surgical procedure. EDX and US studies provide complementary data to determine the severity and the etiology of acute UNE and guide further management.