Large coverage MR neurography in CIDP: diagnostic accuracy and electrophysiological correlation

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Abstract
The objective of this study was to evaluate large coverage magnetic resonance neurography (MRN) in chronic inflammatory demyelinating polyneuropathy (CIDP). In this prospective study, 18 patients with CIDP and 18 healthy controls were examined by a standardized MRN protocol at 3 T. Lumbosacral plexus was imaged by a T2-weighted 3D sequence and peripheral nerves of the upper and lower extremity by axial T2-weighted turbo spin-echo sequences. Lesions were characterized by nerve cross-sectional area (CSA) and T2-weighted signal (nT2). Additionally, T2 relaxometry of the sciatic nerve was performed using a multi-spin-echo sequence. All patients received a complementary electrophysiological exam. Patients with CIDP exhibited increased nerve CSA and nT2 compared to controls (p < 0.05) in a proximally predominating pattern. Receiver operating characteristic analysis revealed the best diagnostic accuracy for CSA of the lumbosacral plexus (AUC = 0.88) and nT2 of the sciatic nerve (AUC = 0.88). CSA correlated with multiple electrophysiological parameters of demyelinating neuropathy (F wave latency, nerve conduction velocity) of sciatic and median nerve, while nT2 only correlated with F wave latency of sciatic and not median nerve. T2 relaxometry indicated that MR signal increase in CIDP was due to an increase in proton-spin-density (p < 0.05), and not due to the increase in T2 relaxation time. Both nT2 and CSA might aid in the diagnosis of CIDP, but CSA correlates more robustly with established electrophysiological parameters for CIDP. Since the best diagnostic accuracy was shown for proximal nerve locations, MRN may be a useful complementary tool in selected CIDP cases.

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