Marieke van Rosmalen

Chapter 4 70 DISCUSSION Quantitative assessment of brachial plexus MRI has acceptable interrater reliability and can be used in the diagnostic workup of patients who may have an inflammatory neuropathy. It can complement NCS and nerve ultrasound for the diagnosis of CIDP, but not MMN. A quantitative assessment of MRI of the brachial plexus and cervical nerve roots with high specificity identified 10% additional patients who responded to treatment but had not been identified by NCS and nerve ultrasound. MRI is part of the current diagnostic criteria for CIDP and MMN and is recommended in particular for the identification of elusive cases, i.e. those without clear NCS abnormalities. 1,2,18–21 This is based on several MRI studies that showed cervical nerve root thickening and increased signal intensity on brachial plexus MRI in a subgroup of patients with chronic inflammatory neuropathies. 7,20 A clear limitation of qualitative assessment of brachial plexus MRI as it is used nowadays is its low interrater reliability. 8,9 Few studies have explored the feasibility and use of a quantitative MRI assessment and only in small groups of patients and healthy controls. 9,22–25 Estimates of the upper limit of normal for cervical nerve root size in healthy controls ranged between 4-5 mm. Analysis of our data from a large cohort of patients with CIDP and MMN showed that combinations of nerve root size are probably more useful than a fixed cut-off. This may be explained by the patchy nature of inflammatory changes. We found that 6 bilateral measurements close to the ganglion of root C5, C6 and C7 in coronal plane was easy to implement in routine practice (3 minutes per subject) and resulted in optimal test characteristics with high specificity levels. Sensitivity levels of quantitative assessment of brachial plexus MRI were lower than those reported in qualitative studies. 23,24 This may be explained by some inclusion bias in earlier studies, as shown by another recent prospective cohort study that also reported a relatively low sensitivity of qualitative brachial and lumbosacral plexus MRI in patients with suspected CIDP. 21 Importantly, test-retest reliability for quantitative measurements was good, which is supported by data from another recent study. 23 We analyzed the diagnostic value of a quantitative assessment of MRI next to NCS and nerve ultrasound studies. 10,12,13 MRI helped to identify patients with a clinical phenotype compatible with CIDP but who did not fulfil the diagnostic criteria of NCS and who did not have ultrasound abnormalities. In this sense, MRI complements nerve ultrasound, which has an excellent sensitivity as shown in previous studies. 10,13 Quantitative assessment of brachial plexus MRI identified an additional 10% of patients who responded to treatment, which is clinically relevant. MRI should therefore be considered as an additional diagnostic tool when there is a strong clinical suspicion of CIDP, particularly when NCS and nerve ultrasound results are normal. Nerve ultrasound, and especially the required expertise, is not always available in all medical centres. In these centres MRI could be used as an additional tool to NCS and laboratory findings, although physicians should always consider the poor sensitivity of MRI when interpreting results.