Marieke van Rosmalen

General discussion 137 8 of nerve roots after infusion with gadolinium while ultrasound only informs on nerve thickness. MRI images tissues in three directions (coronal, sagittal and transversal), and these directions can even be combined in a 3D image, while ultrasound is a 2D imaging technique. MRI is more versatile than ultrasound and has a lot of modalities that are still un- or less-explored. These modalities might be of interest for use in scientific research or clinical practice in the future, for example to study other characteristics than thickening of damaged or injured nerves. Currently explored imaging techniques only show one-dimensional morphological changes (i.e. thickening of damaged or injured nerves and nerve roots) in CIDP and MMN. Other morphological changes still remain at the sub-imaging level. Comparative studies between nerve ultrasound and MRI in patients with CIDP or MMN have been performed but are scarce. One study compared nerve (root) measurements using nerve ultrasound and MRI in patients with CIDP (n = 18) and measured cross-sectional areas of the median, ulnar and radial nerve, and the brachial plexus. They found a positive correlation between nerve ultrasound and MRI measurements in the peripheral nerves ( r = 0.72 – 0.74, p = 0.002 – 0.003), but not in the brachial plexus. 50 Another study compared cross-sectional areas of the median and ulnar nerve on nerve ultrasound and MRI in patients with MMN (n = 10) andALS (n = 10) and also found a positive correlation ( r = 0.60, p < 0.001). 51 This study also showed that both nerve ultrasound and MRI were able to differentiate MMN from ALS. Nerve ultrasound has some advantages over MRI as it is a better tolerated, less-expensive and less time-consuming tool, especially when multiple limbs are imaged. MRI, on the other hand, is widely available. Based on the above mentioned studies ultrasound and qualitative MRI of the peripheral nerves have comparable characteristics. However, the added diagnostic value of measurements of the brachial plexus remains unknown as the CIDP study did not show a correlation between nerve ultrasound and MRI of the brachial plexus, and the MMN study did not image the brachial plexus, while MRI of the brachial plexus is part of the diagnostic criteria of both CIDP and MMN ( Table 8.1 ). 50,51 We therefore evaluated the added diagnostic value of MRI on nerve ultrasound in the last part of our study in chapter 4. We used the developed risk chart in Figure 4.3 with its cut-off values to determine which patients had an abnormal MRI. We found that the majority of patients with abnormal ultrasound findings also had abnormal MRI findings, which corroborates with the comparative studies as earlier described in this paragraph. 50,51 In some patients we found that nerve ultrasound showed thickening while MRI did not. This could be explained by the fact that also the peripheral nerves were imaged with nerve ultrasound while MRI only imaged the brachial plexus, i.e. that this was mainly due to the differences in field-of-view between nerve ultrasound and MRI. The added value of MRI was calculated in the subgroup of patients with CIDP and MMN that did not fulfill the electrodiagnostic criteria for CIDP or MMN and who had no abnormalities on nerve ultrasound. In patients with CIDP we found that 5/50 (10%) patients had an abnormal MRI result, while NCS did not fulfill the electrodiagnostic criteria for CIDP and nerve ultrasound did not show abnormalities. These 5 patients all responded to immunomodulatory treatment. Only one patient with MMN did