Evaluation of atrophy of foot muscles in diabetic neuropathy – A comparative study of nerve conduction studies and ultrasonography☆
Introduction
Diabetic polyneuropathy is characterised by axonal loss combined with demyelination (Malik, 1997). This is reflected in the typical neurophysiological findings including reduced amplitudes of the compound muscle action potentials (CMAP) combined with slowed nerve conduction. The neurophysiological parameters are highly reproducible and reflect the neuropathic process, therefore, they are widely used in clinical studies of diabetic polyneuropathy. Further, longitudinal assessment of the amplitude of the CMAP combined with nerve conduction velocities is used to evaluate the efficacy of treatment (Dyck et al., 1997, Dyck et al., 2005, Kramer et al., 2005).
Using magnetic resonance imaging atrophy of small foot muscles has been found in diabetic patients with polyneuropathy in several studies (Bus et al., 2002, Andersen et al., 2004, Greenman et al., 2005). In one study this was found even in patients without any definite sign of polyneuropathy suggesting that atrophy of small foot muscles may be a sensitive parameter for the detection of neuropathy (Boffeli et al., 2002). Muscle atrophy is an indirect evidence of axonal loss, nevertheless, in diabetic patients atrophy of small foot muscle has attracted great interest because this leads to altered biomechanical properties of the foot such as prominence of the metatarsal heads and clawing of the toes (Boffeli et al., 2002). These changes may ultimately lead to the neuropathic end points foot ulcers and amputation (Rathur and Boulton, 2005). At the hand and foot the CMAPs are recorded from superficially situated muscles and, therefore, the size of the CMAP probably reflects the size of the muscle, however, studies are lacking combining nerve conduction studies with techniques that enable quantification of the target muscles.
In this study the aim was to evaluate whether motor nerve conduction studies provide information about the size of foot muscle. Diabetic patients without and with various degrees of neuropathy were included and the size of the foot muscles was determined by ultrasonography and compared with the findings at conduction studies of the peroneal and the tibial nerve.
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Methods
Twenty-six diabetic patients (22 type 1, 4 type 2) were recruited from the out patient diabetes clinic. Care was taken to include patients without and with various degrees of neuropathy, however, no effort was made to include patients with motor symptoms or deficits. The diabetes duration was 32 (8–42) years (median, range). Patients were examined clinically and examined according to a neurological impairment score that includes activity of tendon reflexes, strength of all major muscle groups
Results
Seventeen patients fulfilled the minimal criteria for diabetic neuropathy and for all patients the neurological impairment score was 14 (0–40). The amplitude of the CMAP was 2.9 ± 2.8 mV (mean ± SD) for the peroneal and 6.2 ± 6.0 mV for the tibial nerve. Correspondingly, the area of the CMAP for the peroneal and the tibial nerve was 8.0 ± 8.7 and 14.6 ± 11.8 msmV, respectively. Nerve conduction velocities were 33.8 ± 12.1 m/s for the peroneal and 35.2 ± 11.8 m/s for the tibial nerve. In 3 and 2 patients,
Discussion
The main finding of this study is that the amplitude of the CMAP and the NCV of the peroneal and the tibial nerve are closely related to the size of small foot muscles determined by US. For the peroneal nerve the relation was closer for the size of the CMAP (amplitude and area) as compared to the NCV indicating that CMAP more closely reflects atrophy of the EDB muscle.
In diabetic neuropathy NCV and CMAP are widely used to monitor the neuropathic process. Quantification of the size of the CMAP
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2017, Clinical Neurophysiology PracticeCitation Excerpt :The reason why we did not see the same result in muscle thickness when comparing trained and untrained men and women separately is probably due to the number of participants being too low when dividing the cohort into subgroups. The finding that the CMAP amplitude of the EDB muscle correlates with muscle thickness in the whole cohort is in line with a previous study (Seok et al., 2016), and similar correlations has also been found in foot muscles of diabetic patients (Severinsen and Andersen, 2007). One drawback of the study was that the untrained group was older than the trained group.
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Disclosures: The authors have no disclosures.