Longitudinal five-year follow-up by muscle MRI and high-resolution nerve ultrasound in hereditary neuropathies.

Abstract

Background and aims: Hereditary polyneuropathies are rare heterogeneous neurological disorders that cause progressive muscle weakness and disability. As new therapies emerge, sensitive imaging biomarkers to monitor disease progression are essential. This exploratory longitudinal study evaluated MRI with focus on the lower limbs and high-resolution ultrasound (HRUS) at two points over the period of 4.75 years in genetically confirmed patients, and compared imaging with clinical and electrophysiological findings.

Methods: Fourteen patients (CMT1A, CMT1X, CMT1B, CMT1C, CMT2, and hereditary myoneuropathy) underwent standardized clinical examinations, including Charcot-Marie-Tooth Examination Score version 2 (CMTESv2), Medical Research Counsil muscle strength, and sensory testing. Nerve conduction studies (NCS) were performed on upper limb nerves. MRI of lower limbs evaluated muscle volume, normalized T1w signal intensity (nSI), and proton density fat fraction (PDFF). HRUS was used to assess nerve cross-sectional areas, the ultrasound pattern sum score (UPSS), and muscle echogenicity.

Results: Over the observation interval, patients showed a significant increase in CMTESv2 (p = 0.0031), especially in motor symptoms (p = 0.0012). MRI-derived muscle volumes did not change; however, nSI significantly increased in gastrocnemius lateralis muscles (p = 0.0023), indicating progressive fat infiltration. UPSS increased in demyelinating polyneuropathies (p = 0.0299) and was inversely correlated with nerve conduction velocities of the median (p = 0.0413) and ulnar nerves (p = 0.0064).

Interpretation: Over this 5-year interval, our cohort showed clinical disease progression, which was not reflected by NCS and MRI volumetry. In contrast, MRI-derived nSI correlated with PDFF and captured progressive muscle fat replacement, correlating with declining muscle strength. UPSS showed longitudinal progression in demyelinating neuropathies. PDFF and UPSS are promising biomarkers and may support outcome evaluation in future clinical trials.