Quantitative assessment of sciatic nerve changes in Charcot-Marie-Tooth type 1A patients using magnetic resonance neurography.

BACKGROUND AND PURPOSE: Nerve tissue alterations have rarely been quantified in Charcot-Marie-Tooth type 1A (CMT1A) patients. The aim of the present study was to quantitatively assess the magnetic resonance imaging (MRI) anomalies of the sciatic and tibial nerves in CMT1A disease using quantitative neurography MRI. It was also intended to seek for correlations with clinical variables. METHODS: Quantitative neurography MRI was used in order to assess differences in nerve volume, proton density and magnetization transfer ratio in the lower limbs of CMT1A patients and healthy controls. Disease severity was evaluated using the Charcot-Marie-Tooth Neuropathy Score version 2, Charcot-Marie-Tooth examination scores and Overall Neuropathy Limitations Scale scores. Electrophysiological measurements were performed in order to assess the compound motor action potential and the Motor Unit Number Index. Clinical impairment was evaluated using muscle strength measurements and Charcot-Marie-Tooth examination scores. RESULTS: A total of 32 CMT1A patients were enrolled and compared to 13 healthy subjects. The 3D nerve volume, magnetization transfer ratio and proton density were significantly different in CMT1A patients for the whole sciatic and tibial nerve volume. The sciatic nerve volume was significantly correlated with the whole set of clinical scores whereas no correlation was found between the tibial nerve volume and the clinical scores. CONCLUSION: Nerve injury could be quantified in vivo using quantitative neurography MRI and the corresponding biomarkers were correlated with clinical disability in CMT1A patients. The sensitivity of the selected metrics will have to be assessed through repeated measurements over time during longitudinal studies to evaluate structural nerve changes under treatment.

Quantitative sudomotor test helps differentiate transthyretin familial amyloid polyneuropathy from chronic inflammatory demyelinating polyneuropathy.

OBJECTIVE: Transthyretin familial amyloid polyneuropathy (TTR-FAP) is an aggressive hereditary neuropathy characterized by sensory and autonomic dysfunction. There are numerous reports of TTR-FAP misdiagnosed and treated as chronic inflammatory demyelinating polyneuropathy (CIDP), leading to delayed diagnosis, risk of iatrogenic adverse events and increased socio-economic costs. Quantitative sudomotor function measured by electrochemical skin conductance (ESC) appears to be a sensitive test in TTR-FAP. We aimed to evaluate the performance of ESC in differentiating TTR-FAP from CIDP. METHODS: Thirty-eight patients with genetically confirmed hereditary TTR amyloidosis and 26 with definite CIDP according to the EFNS/PNS guidelines and negative TTR-FAP genetic testing were involved in this study. We compared the ESC for feet and hands measured by Sudoscan for each patient. RESULTS: ESC (µS) was significantly lower in TTR-FAP for both hands (72 vs 45, p < 0.0001) and feet (77 vs 35, p < 0.0001). Feet ESC < 64 µS had a 89% sensitivity and a 96% specificity to differentiate between CIDP and TTR-FAP. CONCLUSION: Sudoscan is a fast, non-invasive and easy to perform test, able to distinguish CIDP and TTR-FAP patients with good sensitivity and specificity. SIGNIFICANCE: Sudoscan can be helpful in distinguishing between CIDP and TTR-FAP.