Magnetic Resonance Neurography in Spontaneous Radial Neuropathy: An Unexpectedly High Rate of Nerve Constriction

INTRODUCTION/AIMS: Magnetic resonance (MR) neurography has enabled the detection of subtle intraneural abnormalities, such as focal constrictions. This study aimed to describe the MR neurography findings in patients with spontaneous radial neuropathy. METHODS: Patients with spontaneous radial neuropathy symptoms for > 3 months and with electromyographically confirmed radial neuropathy at our hospital from 2018 to 2023 were initially included. Among these, data from patients who underwent MR neurography were analyzed. Abnormal nerve findings were defined as the presence of increased signal intensity, enlargement, constriction, and/or loss of the fascicular pattern on MR neurography. Patients with abnormal nerve findings were categorized into two groups based on the presence or absence of constriction, and the differences in demographics, clinical symptoms, and treatment outcomes were compared. RESULTS: Of 27 patients (19 males; mean age 47 years), abnormal nerve findings were observed in 23 (85%) patients, of whom 13 (48%) had constrictions. Three patients (11%) exhibited no nerve abnormalities, whereas one patient had a tumor (malignant peripheral nerve sheath tumor). Nerve constrictions were most frequently observed proximal to the elbow joint, with a median location of 21 mm proximal to the joint (interquartile range [IQR], -2 to 77 mm). The patients with constriction were significantly younger (32 vs. 63 years, p < 0.001) and exhibited a higher prevalence of left-sided involvement (85% vs. 20%, p = 0.002). DISCUSSION: The relatively high frequency of nerve constriction suggests that MR neurography may be valuable in guiding further management, including possible surgical intervention. LEVEL OF EVIDENCE: III.