Evaluating neurological injury in Hirayama disease using threshold tracking technology

Abstract

Objective To investigate the efficacy of neurological injury in patients with Hirayama disease using threshold tracking technique. Methods This study included 17 patients with Hirayama disease who visited the Department of Orthopaedics of Huashan Hospital from June 2017 to October 2017 (patient group, 16 males and 1 female, the average age was 18.06±0.50 years, ranging from 16 to 22 years, the average course of disease was 27.2±18.81 months, ranging from 1 to 60 months. Meanwhile, a total of 20 healthy volunteers (control group, 19 males and 1 female, the average age is 20.05±1.30 years, ranging from 17 to 23 years) were also enrolled in this study. In patient group, the median motor nerve conduction examination, needle EMG examination, and threshold tracking examination were performed on the severe side; while in control group, the median motor nerve conduction examination and threshold tracking examination were performed on either side. We evaluate the changes in peripheral motor nerve conduction of Hirayama disease by comparing CMAP (compound muscle action potential) and median motor nerve conduction velocity evaluate the changes in motor nerve excitability by comparing the rheobase, SDTC (Strength-duration time constant), threshold electrotonus, current-threshold I/V slope, superexcitability, and subexcitability. The upper limb function was assessed by disabilities of arm, shoulder and hand (DASH) score. The differences in threshold tracking parameters between groups were compared by independent t test, and the correlation between SDTC and DASH score was tested by Pearson correlation analysis. Results In the peripheral motor nerve conduction examination, the median nerve CMAP in patients with Hirayama disease was 4.12±1.43 mV in average, which is lower than healthy controls 8.23±1.61 mV (t=-3.8, P<0.01). There was no significant difference in the peripheral motor nerve conduction velocity (t=-0.86, P=0.39). In the threshold tracking examination, SDTC in patients with Hirayama disease was 0.48±0.09 ms, which was prolonged than healthy controls 0.39±0.06 ms (t=3.75, P<0.01). The absolute values of TEh (10-20) and TEh (20-40) decreased significantly (P<0.01), hence, the hyperpolarized part of the threshold-electrotonus curve showed fanning-in pattern. The slope of the current-threshold (I/V) curve had a decreasing trend. The hyperpolarized I/V slope in patients with Hirayama disease was 0.27±0.09 in average, which was lower than the healthy controls which was 0.34±0.07 (t=-2.73, P=0.01). The DASH score of patients ranged from 0.86 to 19.44, with an average of 6.99±5.79. There was a correlation between SDTC and DASH score, R2=0.36, which met the F test (P=0.01). Conclusion Threshold tracking technique can be adapted in evaluating nerve injury in Hirayama disease to determine the degree of injury and potential pathogenesis. Key words: Cervical vertebrae; Spinal cord compression; Upper extremity; Muscular atrophy; Spinal fusion; Electromyography