MRI biomarkers of proximal nerve injury in CIDP

Abstract

Objective: To evaluate the utility of nerve diffusion tensor imaging (DTI), nerve cross-sectional area, and muscle magnetic resonance imaging (MRI) multiecho Dixon for assessing proximal nerve injury in chronic inflammatory demyelinating polyneuropathy (CIDP).

Methods: In this prospective observational cohort study, 11 patients with CIDP and 11 healthy controls underwent a multiparametric MRI protocol with DTI of the sciatic nerve and assessment of muscle proton-density fat fraction of the biceps femoris and the quadriceps femoris muscles by multiecho Dixon MRI. Patients were longitudinally evaluated by MRI, clinical examination, and nerve conduction studies at baseline and after 6 months.

Results: In sciatic nerves of CIDP patients, mean cross-sectional area was significantly higher and fractional anisotropy value was significantly lower, compared to controls. In contrast, muscle proton-density fat fraction was significantly higher in thigh muscles of patients with CIDP, compared to controls. MRI parameters showed high reproducibility at baseline and 6 months.

Interpretation: Advanced MRI parameters demonstrate subclinical proximal nerve damage and intramuscular fat accumulation in CIDP. Data suggest DTI and multiecho Dixon MRI might be useful in estimating axonal damage and neurogenic muscle changes in CIDP.

Figure 1

T2 of the sciatic nerve (A and B) High‐resolution axial T2 image of the right thigh. Compared to controls (B), in patients with CIDP (A) the cross‐sectional area of the sciatic nerve appeared enlarged and individual fascicles of the sciatic nerve were distinguishable (arrow). (C) Nerve cross‐sectional area was significantly higher in patients with CIDP.

Figure 2

Tractography and fractional anisotropy (FA) in the proximal sciatic nerve segment of patients with CIDP and healthy controls. (A, B) Illustration of FA (fractional anisotropy) sampling location in a sagittal mid‐section 3D T2 TSE‐image of a patient with CIDP (A) and a healthy control (B). The course of the sciatic nerve is visualized by deterministic fiber tracking. Subjects right‐sided thighs were positioned deep into the Tx/Rx 8‐channel knee coil to have the center of the DTI stack and hence the FA sampling location positioned 10–20 cm cranially of the patella's upper edge (Fiber tractography was performed with IntelliSpace Portal 7.0, Philips Healthcare, Amsterdam, The Netherlands). (C) Average FA values of sciatic nerves are lower in patients with CIDP at baseline (t0) and at 6 months follow‐up (t1) compared to healthy controls.

Figure 3

Fat quantification of thigh muscles by multiecho Dixon sequence. (A and B) Multiecho Dixon quantitative proton‐density fat fraction map of the right thigh of a patient with CIDP (A) and a healthy control (B). Subtotal intramuscular ROIs were drawn on these maps to quantify the fat fraction. Visually inspected, the higher intramuscular signal reflects the increased fat fraction going along with neurogenic muscle atrophy. Note that artifacts surrounding the thigh have been removed by software postprocessing. (C) Average intramuscular fat fractions in the biceps femoris and quadriceps muscles. Fat fractions were higher in the quadriceps and biceps femoris muscles in patients with CIDP at baseline (t0) and 6 months later (t1), compared to healthy controls. (D, E) Correlations between sciatic nerve cross‐sectional area and biceps femoris fat fraction. Correlations were statistically significant at 6 months (t1, E) but not at baseline (t0, D).