American Society for Peripheral Nerve

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Mechanical Allodynia Predicts Better Outcome Of Nerve Decompression For Painful Diabetic Peripheral Neuropathy: Indications Of A Sequential Compression Impairment Of Peripheral Nerve Fibers
Chenlong Liao, MD; Wenchuan Zhang, MD; XinHua
Hospital affiliated to Shanghai JiaoTong University School of Medicine, Shanghai, China

As one of the most common complications of diabetes mellitus, diabetic peripheral neuropathy (DPN) has become a worldwide concern. DPN has traditionally been considered to be an irreversible and progressive condition until Dellon in 1988 proposed surgical decompression of multiple peripheral nerves based on the hypothesis of "double crush" and evidence of metabolically induced nerve trunk enlargement and resultant entrapment at anatomic fibro-osseous tunnels. The pain associated with DPN can occur spontaneously or alternatively provoked by mild nocuous (hyperalgesia) or innocuous (allodynia) stimuli. Our clinical observations suggested that cases with the common mechanical allodynia (MA) of DPN were responding better to surgical treatment. This study examines MA and relates it retrospectively to outcomes of surgical nerve decompression (ND) on several subjective and objective measures. Our results led us to propose a hypothesis of sequential compression impairment and differential susceptibility of nerve fiber types which could explain individual difference in clinical presentations and varied ND outcomes.

Materials and Methods
A series of 192 patients with painful DPN was collected in this study, with 148 patients in the surgical group and 44 patients in the control group. Both groups were further divided into subgroups based on the occurrence of mechanical allodynia on admission. Signs of MA were detected in 65 patients in the surgical group and 19 patients in the control group. Clinical evaluations including visual analogue scale (VAS), nerve conduction velocity (NCV) and high-resolution ultrasonography (cross-sectional area, CSA) were performed on admission prior to surgery and also during the follow-up. The follow-up was set at an 3-6 months intervals after surgery.

The levels of VAS and HADS, the results of NCV and CSA were improved in the surgical group (P<0.05). In the surgical subgroups, pain reduction, psychiatric amelioration, improvement in NCVs and the restoration of the CSA were observed in patients with sign of MA (P<0.05), while only pain reduction, psychiatric amelioration and restoration of the CSA were noted in patients without sign of MA (P>0.05). Furthermore, better pain reduction was achieved in patients with MA when compared with those without MA (P<0.05).

Better Pain relief and improvement in NCVs were achieved in patients with positive sign of MA, which, therefore, is a reliable predictor on better surgical outcome for painful DPN. Application of this information should be helpful in the selection of painful DPN patients likely to benefit from ND.

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