MR microneurography and quantitative T2 and DP measurements of the distal tibial nerve in CIDP
Introduction
Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired, immune-mediated inflammatory disorder causing demyelinating peripheral neuropathy with a slowly progressive or relapsing course.
The estimated prevalence is 8.9 per 100,000 people and although it is a rare medical condition, CIDP encompasses ca. 13% of all cases of neuropathy referred to neuromuscular clinics [1,2]. The diagnosis of CIDP is based on a multi-criteria algorithm, including clinical examination, nerve conduction studies (NCS), and cerebral spinal fluid examination, but imaging techniques such as MRI and ultrasound (US) are increasingly used to support the diagnosis, assessment of the clinical course and response to treatment.
Typical findings in CIDP include nerve enlargement, T2 signal increase and enhancement of nerve roots, especially at the first stages of the disease [3]. Proximal nerve involvement is typical at the onset and becomes more prominent and ubiquitous in the long-term. Nerve enlargement is also positively correlated with disease duration [[4], [5], [6]]. However, correlation of MRI features with clinical disability or response to treatment is controversial [7] and reliable biomarkers of disease detection and progression are still lacking.
Most previous works on MRI of CIDP were focused on the spinal nerve roots and proximal nerve trunks, and there is a paucity of works on the distal involvement of nerves [8]. The extremities can be imaged with smaller surface coils reaching greater resolution, allowing direct visualization of nerve ultrastructure. In previous studies, we have shown the possibility to visualize the tibial nerve at the ankle with microscopic resolution, using a standard clinical set of MRI hardware and sequences [[9], [10], [11]]. With these techniques, in plane resolution up to 100 μm can be reached allowing direct visualization of the nerve fascicles, the epineurium, the perineurium and fat infiltration.
In this study we evaluated the role of MR micro-neurography in detecting morphological, structural and relaxometric changes in distal tibial nerves in patients affected with CIDP, and their correlation with clinical and electrophysiological features. In particular, we investigated the diagnostic potential of morphologic features such as the number of fascicles (N), their mean diameter (FD), the total area of fascicles (FA), epineurium (EA), nerve (NA) and the fascicle to nerve area ratio (FNR), and quantitative relaxometric parameters such as T2 and proton density (PD).
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Subjects and clinical evaluation
This study was approved by our institutional review board and all subjects provided written informed consent. We included a convenience sample of 10 CIDP patients with variable disease and treatment duration who met the European Federation Society/Peripheral Nerve Society definite diagnostic criteria for CIDP [12]. Ten healthy subjects matched by sex and age were imaged as a control group. The controls were excluded if they had either clinical evidence or past history of lumbar roots
Results
A total of 10 patients affected with CIDP were imaged (7 men and 3 women; age range 31–74, median 64 years). Detailed demographics of the patients are shown in Table 1. Mean age of onset was 54 years (range 10–74, SD 19.4), with an average disease duration at the time of the study of 8,8 years (range 1–20, SD 6.8). Median INCAT-LL disability score was 2 (range 0–3), median ISS-LL score 4.5 (range 2–8), median MRC-LL 30 (range 28–30); MRC-APF was maximum (5) for all patients. The clinical course
Discussion
In this study we investigated the diagnostic potential of MR microneurography, a novel technique capable to assess the ultrastructure of nerves, in distinguishing patients affected with CIDP and normal subjects. Multiple morphological and relaxometric parameters were assessed and correlations with clinical features and disease severity were explored. We have found significant increases in total NA and FA in CIDP patients, however, none of the parameters investigated was significantly correlated
Conflict of interest disclosure
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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