Relationships Between Nerve Ultrasound Findings and Clinical, Genetic, Laboratory and Electrophysiological Findings in Patients With Chronic Idiopathic Axonal Polyneuropathy.

INTRODUCTION/AIMS: Chronic idiopathic axonal polyneuropathy (CIAP) is an increasingly recognized, frequent and often disabling disease with unknown etiology. We explored the utility of nerve ultrasound in the investigation of patients with predominantly sensory CIAP, by comparing ultrasound with clinical, genetic, laboratory and electrophysiological findings.

METHODS

Thirty-nine patients with a predominantly sensory CIAP were included. The averaged measurements of the ultrasound cross-sectional areas (CSAs) of median and ulnar nerves at mid-forearm and mid-humerus (Mean UL CSAs) for each patient were compared with demographics, neuropathy scores (INCAT Sensory Sumscore (ISS) and Toronto Clinical Neuropathy Score), blood tests, repeat nerve conduction studies and, given the RFC1 association with late-onset sensory neuropathy, genetic RFC1 testing.

RESULTS

Mean UL CSA was significantly reduced in six patients (4.3 ± 0.6 mm2), increased in 15 (10.2 ± 2.1 mm2) and normal in 18 (6.7 ± 0.7 mm2). Ultrasound abnormalities were associated with two distinct phenotypes: Most of the six patients with small CSAs had normal (five patients) or only mildly elevated body mass index (BMI), were homozygously RFC1 expansion positive (four) and had a possible sensory neuronopathy based on Camdessanché criteria (five). Most patients with enlarged CSAs were overweight (93%), a majority had obesity (67%) and none was RFC1 positive.

DISCUSSION: This exploratory study supports a role for ultrasound in the differential diagnosis of CIAPs: reduced CSAs of upper limb nerves suggest inherited sensory neuronopathy, whereas increased CSAs make inherited sensory neuronopathy unlikely and, in combination with obesity, suggest metabolic neuropathy. Larger confirmatory studies are needed.