Median nerve ultrasonography in distinguishing neuropathy sub-types: a pilot study

The diagnostic potential of ultrasonography (US) in polyneuropathy has been studied rarely, with complex measurement/correction techniques. Whether US may be useful in clinical practice remains uncertain.

We aimed to ascertain the value of US, as performed routinely at our institution, in differentiating neuropathy sub-types. We prospectively studied 14 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and 14 patients with sensory axonal neuropathy (SAN). Median nerves were studied bilaterally at wrist and forearm by a radiologist blinded to the neuropathy sub-type. Nerve width (medial to lateral diameter), thickness (anterior to posterior diameter) and cross-sectional area were compared in between patient groups and anatomical sites. Optimal cut-off values were determined using receiver operating characteristic (ROC) curves.

Largest measured median nerve thickness was significantly greater in patients with CIDP (P = 0.014), and ROC curve analysis indicated a cut-off offering a sensitivity of 57.1% for CIDP and specificity of 92.9% vs SAN. Nerves were wider and had larger cross-sectional areas, but were not thicker, at wrist compared to forearm in both patient groups. There was an equal prevalence in both patients with CIDP and SAN, of increased median nerve wrist-to-forearm area ratio, compatible with sub-clinical carpal tunnel syndrome.

This prospective, blinded, pilot study is the first to indicate the diagnostic potential of US, as performed routinely, in distinguishing between acquired demyelinating and axonal neuropathy. These findings now require confirmation in larger, adequately designed studies, evaluating other nerves/nerve sites, assessing healthy controls and taking into account interrater and equipment variabilities.