J Neurosurg Spine. 2015 Dec;23(6):707-14.

Electrophysiological assessments of the motor pathway in diabetic patients with compressive cervical myelopathy.

  • 1Department of Orthopedic Surgery, Integrated Health Sciences, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.

 

Abstract

OBJECT: The occurrence of compressive cervical myelopathy (CCM) increases in adults over 50 years of age. In addition, diabetes mellitus (DM) is a frequent comorbidity for people of this age and may impact the severity of CCM. The authors assessed motor pathway function in diabetic patients with CCM to investigate the correlation between electrophysiological parameters and clinical symptoms.

METHODS: Motor evoked potentials (MEPs) were measured from the abductor digiti minimi muscle (ADM) and the abductor hallucis muscle (AH) following transcranial magnetic stimulation, as were M- and F-waves following electrical stimulation of the ulnar and tibial nerves, in 22 patients with CCM and diabetes mellitus (DM) who had not experienced symptomatic diabetic neuropathy (CCM-DM group), in 92 patients with CCM alone (CCM group), and in 24 healthy adults (control group). The peripheral conduction time (PCT; measured from the ADM and AH) was calculated as follows: (M-wave latency + F-wave latency -1)/2. The central motor conduction time (CMCT; measured from the ADM and AH) was calculated by subtracting the PCT from the onset latency of the MEPs. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was obtained before and 1 year after surgery as a clinical outcome measure.

RESULTS:MEP, PCT, and CMCT parameters in the CCM-DM and CCM groups were significantly longer than those in the control group (p = 0.000-0.007). The PCTs in the CCM-DM group were significantly longer than those in the CCM group (p = 0.001-0.003). No significant differences were detected in the MEP and CMCT parameters between the CCM-DM and CCM groups (p = 0.080-1.000). The JOA score before surgery in the CCM-DM group was 10.7 ± 2.0 points and was significantly lower than that in the CCM group (12.2 ± 2.5 points, p = 0.015). In the CCM-DM group, JOA scores before surgery correlated with MEP-AH (r = -0.610, p = 0.012) and PCT-AH (r = -0.676, p = 0.004) values, but not with CMCT values, while the JOA scores were related to both MEP and CMCT parameters in the CCM group. The JOA scores improved to 13.8 ± 2.2 points after surgery (p = 0.001) and correlated with MEP-AH (r = -0.667, p = 0.005) and PCT-AH (r = -0.611, p = 0.012) in the CCM-DM group.

CONCLUSIONS:The results suggest that MEP, PCT, and CMCT parameters each reveal abnormalities in the upper and lower motor neurons even in patients with DM. The results also show a prolonged PCT in CCM-DM patients, despite having no history of diabetic neuropathy. Corticospinal tract impairments are similar between CCM and CCM-DM patients, while the JOA score of the CCM-DM patients is lower than that in the CCM patients. The JOA score in CCM-DM patients may be influenced by additional impairments in peripheral nerves or other diabetic complications. These electrophysiological studies may be useful for screening motor pathway function for CCM in patients with DM.

KEYWORDS: ADM = abductor digiti minimi muscle; AH = abductor hallucis muscle; BMI = body mass index; CCM = compressive cervical myelopathy; CMAP = compound muscle action potential; CMCT = central motor conduction time; CSM = cervical spondylotic myelopathy; DM = diabetes mellitus; F-wave; JOA = Japanese Orthopaedic Association; MEP = motor evoked potential; OPLL = ossification of the posterior longitudinal ligament; PCT = peripheral conduction time; TMS = transcranial magnetic stimulation; central motor conduction time; cervical; cervical myelopathy; corticospinal tract; diabetes mellitus; motor evoked potentials; peripheral conduction time; transcranial magnetic stimulation

PMID: 26340381

 

Supplement:

Compressive cervical myelopathy (CCM) is a prevalent and increasingly observed neurological disorder in adults during and after middle age. Distinctive symptoms of CCM are numbness in the extremities, clumsiness in the hands, spastic gait disturbance, and bladder and bowel dysfunction. Diabetes mellitus (DM) is a frequent comorbidity and can cause numbness and weakness in the extremities due to peripheral neuropathy. In fact, it is sometimes difficult to evaluate the severity of spinal cord deterioration in DM patients with CCM. Therefore we assessed motor pathway function in diabetic patients with CCM to investigate the correlation between the Japanese Orthopaedic Association (JOA) score for cervical myelopathy (JOA score) and electrophysiological parameters, which included central motor conduction time (CMCT) and peripheral conduction time (PCT).

In the results, the CMCT and PCT parameters each reveal abnormalities in the upper and lower motor neurons in patients with DM. Corticospinal tract impairments are similar between CCM and CCM-DM patients, while the JOA score of the CCM-DM patients is lower than that in the CCM patients, suggesting that the JOA score in CCM-DM patients may be influenced by additional impairments in peripheral nerves or other diabetic complications. We consider that these electrophysiological studies may be useful for screening motor pathway function for CCM in patients with DM. We show the representative case following.

 

Fig1AFig 1A

Fig1B

Fig 1B

 

Illustrative Case

A 71 year old gentleman reported spastic gait disturbance over the previous a year. He had diabetes mellitus for the 2 years. The patient presented with numbness in the hands and feet, clumsiness in the hands, increased patella tendon reflex, and frequent urination. The JOA score was 7 points. T2 weighted MRI demonstrated severe canal stenosis in the C3-4, C4-5, and C5-6 levels (Fig. 1A).

Motor evoked potentials (MEPs) following transcranial magnetic stimulation (MEP-ADM/AH), as well as M- and F-waves following electrical stimulation of the ulnar and tibial nerves were measured from the abductor digiti minimi muscle (ADM) and abductor halluces muscle (AH). Then, the peripheral conduction time (PCT-ADM/AH) and central motor conduction time (CMCT-ADM/AH) was calculated. The MEP-ADM/AH latencies were 35.4/57.6ms in the right side and 34.1/66.2ms in the left side (Fig. 1B). The PCT-ADM/AH values were 18.15/39.45ms in the right side and 18.25/38.9ms in the left side, respectively. The CMCT-ADM/AH values were 17.25/18.15ms and 15.85/27.3ms,respectively. All those values were significantly prolonged, compared to the normal values (MEP-ADM/AH: 20.4±1.5/38.2±2.2ms; PCT-ADM/AH: 13.0±0.99/23.9ms±1.9; CMCT-ADM/AH: 7.4±1.0/14.3±1.1ms). A cervical laminoplasty was performed. Then, the JOA score improved to 11 points after a year.

In this way, the MEP, PCT, and CMCT can reveal abnormalities in upper and lower motor neurons, respectively in patients with DM. These electrophysiological studies may be effective for screening motor pathway function non-invasively for CCM patients, even in diabetic patients.

 

 

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