Relationship between Clinical Severity and Cross-sectional Area of Ultrasonographic Examinations in Ulnar Neuropathy at the Elbow

OBJECTIVES: This study explored the relationship between clinical severity of ulnar neuropathy at the elbow (UNE) and ulnar nerve cross-sectional area (CSA) by ultrasound examination to identify appropriate measurement sites for UNE diagnosis and evaluation. METHODS: In this retrospective analysis, we examined the arms of 37 patients diagnosed with UNE and those of 34 individuals as controls. The ulnar nerve CSAs were measured at 2 cm distal to the tip of the medial epicondyle (dME), the tip of the medial epicondyle (ME), 2 cm proximal to the tip of the medial epicondyle (pME), and any site showing the maximum CSA between the dME and pME (largest dpME). The modified McGowan classification (grades I, IIA, IIB, and III) was used to rate the clinical severity of UNE. RESULTS: For all sites, the CSAs were significantly correlated with clinical severity. The sites showing the maximum CSA were inconsistent between controls and grade IIA patients. Grade IIB patients showed the largest CSA at the ME in the majority of patients. In grade III patients, maximum CSA occurred only at the ME. CONCLUSIONS: Serial assessment to detect nerve enlargement at multiple sites was beneficial for mild UNE patients with weakness of the ulnar distal muscles with Medical Research Council (MRC) score of 4 or higher (grade IIA). For severe UNE patients with weakness of the ulnar distal muscles classified as MRC3 or less (grades IIB, III), the most efficient method for detecting enlarged nerves was to initially measure the CSA at the ME.