Muscle magnetic resonance imaging of denervation and reinnervation: correlation with electrophysiology and histology
Introduction
The diagnosis of peripheral nerve lesions is commonly based on clinical and electrophysiological examination. Recently, magnetic resonance imaging (MRI) of nerve and muscle has been introduced in the diagnostic workup of neuromuscular disorders. On muscle MRI, a prolongation of both the T1 and T2 relaxation times after denervation has been described (Polak et al., 1988). Changes of the T2-relaxation time are present as early as 24–48 h after denervation (Bendszus et al., 2002). Moreover, gadolinium-DTPA (Gd-DTPA) uptake of denervated muscle has been described at 48 h after denervation (Bendszus and Koltzenburg, 2001). Lately, a clinical study demonstrated a comparable diagnostic accuracy of MRI in neuromuscular disorders compared to the gold standard of clinical and electrophysiological examination (Bendszus et al., 2003). However, despite the remarkable progress of MRI in diagnosing neurogenic muscle changes, very little is known about the time course and pathophysiology of the MR signal alterations and their relation to electrophysiological abnormalities. In the present study, we sequentially examined the MR muscle relaxation time changes following denervation and reinnervation in relation to the electrophysiological findings. Moreover, we quantified histopathological abnormalities in muscle tissue at corresponding time points to study the pathophysiological basis of the MR signal alterations.
Section snippets
Methods
Animal studies were approved by the local animal care committee and carried out in accordance with German law. At the end of the study animals were killed by an overdose of anesthetic. MRI, electrophysiology, and histology were applied in three different series of animals using the identical model of nerve lesion.
MRI
The denervated muscle showed hyperintense signals on T2-w images as early as 2 days after the lesion with a subsequent signal increase until week 4 (Fig. 1). Twenty-four hours after denervation, there was no increase in the T2-relaxation time in the soleus muscle (40.7 ± 0.4 vs. 41.2 ± 0.4 ms, P = 0.9), peroneal muscle (42.3 ± 0.7 vs. 43.1 ± 0.4 ms, P = 0.09), or the gracilis muscle (41.8 ± 0.3 vs. 41.3 ± 0.7 ms, P = 0.2). However, 48 h after the nerve lesion, both the soleus (40.7 ± 0.4 vs.
Discussion
A prolongation of the T2 relaxation time of denervated muscle was first described by Polak et al. (1988). Since then several clinical and experimental studies have confirmed these MR signal changes after denervation Fleckenstein et al., 1993, Grant et al., 2002, Hayashi et al., 1997, Küllmer et al., 1998, West et al., 1994. Recently, gadolinium-DTPA enhancement has been reported in denervated muscle (Bendszus and Koltzenburg, 2001).
As MRI is about to be established as an important tool in the
Acknowledgements
We thank Tanja Horn, MS, for helping with the MRI measurements and data analysis.
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Present address: Institute of Neurology, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK.