Diagnostic Accuracy of Median Nerve Cross-Sectional Area in Suspected Amyotrophic Lateral Sclerosis

Reduced nerve sizes obtained by nerve ultrasound (NUS) have been proposed as a potential diagnostic marker for amyotrophic lateral sclerosis (ALS). However, prospective studies evaluating patients with suspected ALS are currently lacking. We, therefore, evaluated the diagnostic accuracy of a standardized NUS protocol in a large sample of suspected ALS patients.

We prospectively recruited 193 patients with suspected ALS, all of whom underwent the relevant ancillary tests. They also underwent a standardized NUS protocol, evaluating median nerve cross-sectional area (CSA) at upper arm, forearm and wrist. Additionally, we selected, retrospectively, a random sample of incident patients with multifocal motor neuropathy (MMN, n = 42). We determined diagnostic accuracy using receiver operating characteristic (ROC) analysis.

Ultimately, 143/193 patients received a final diagnosis of ALS, at a median disease duration of 10 months. Fifty patients were classified as non-ALS. Diagnostic yield of NUS to distinguish between patients with and without ALS was low (highest area under the curve (AUC) at the wrist: 0.57). In contrast, abnormal nerve sizes accurately discriminated MMN from patients with ALS, with AUCs ranging from 0.65 at the wrist to 0.86 at the upper arm.

Our study shows that reductions in nerve size are unlikely to have diagnostic utility during routine evaluation of suspected patients with ALS. However, when the differential diagnosis includes both ALS and MMN, median nerve size demonstrates high diagnostic accuracy.