Lower extremity nerve decompression in painful diabetic polyneuropathy

Abstract

The aim of the study was to evaluate the effect of surgical decompression of nerves in the lower extremity in patients with painful diabetic polyneuropathy (DPN). Influences on pain, tactile sensation, anatomical aspects of the tibial nerve and thickness of the flexor retinaculum, use of pain medication, nerve conduction studies, postural stability and functional status of the patients were studied. Over a period of two years, 42 patients with painful DPN who met inclusion criteria were enrolled in the Lower Extremity Nerve entrapment Study (LENS). The intervention consisted of surgical decompression of the tibial nerve and its three branches at the ankle site and the common peroneal, deep peroneal and superficial peroneal nerve in one limb. The contralateral limb was treated with usual care and served as control: ‘within-patient comparison’. To evaluate pain, a Visual Analogue Scale (VAS) was used. Sensibility was tested with a Semmes Weinstein monofilament and two-point discriminator at nine predetermined plantar sites of the foot. Prescription data for pain medication were collected and compared and the Medication Possession Rate (MPR) was used for evaluation of therapy adherence per patient. All subjects underwent ultrasound examination of the tibial nerve and flexor retinaculum at the ankle. The software calculated the cross sectional area (CSA) of the nerve. Nerve conduction studies (NCS) were performed and a sensitive pressure mat was used to investigate the effect on static balance. To study the effect on health related quality of life (HRQoL) and to determine minimal clinically important differences (MCID) in pain- and HRQoL scores the 36-Item Short-Form Health Survey (SF-36) and EuroQol 5 dimensions (EQ-5D) questionnaires were filled out. We proved that decompression of the tibial nerve and its three branches and the common peroneal, superficial peroneal and deep peroneal nerve, in patients with painful DPN significantly reduces pain, measured with the VAS, during the total follow up period of one year. In 42.5 % of the patients the alleviation of pain is clinically meaningful with a VAS reduction of 2.9 at 12 months. In spite of this result, no significant effect on quality of life was measured at the end of the study. The effect of surgery had only a temporarily positive effect on the use of pain medication. Correct prescription of pain medication according to the Dutch guideline by doctors and therapy adherence by patients were suboptimal. Patients with painful DPN have a more swollen tibial nerve at the ankle site, at the same time the covering flexor retinaculum is thicker than in healthy people. No effect, however, on CSA was seen after decompression. Furthermore, one year after decompression no positive effect was seen in motor and sensory nerve conduction studies, which supports the non-significant differences at twelve months on stability and sensory tests. Based on the results of this study, we suggest to add surgical decompression of nerves in the lower extremity in patients with painful DPN as a treatment modality when medication fails to achieve decrease of pain symptoms or when medication leads to intolerable side effects.