Outcomes after Cervical Duraplasty for Monomelic Amyotrophy (Hirayama Disease): Results of a Case–Control Study of 60 Patients

Background The optimal management and the role of surgery in monomelic amyotrophy, also known as Hirayama disease (HD), remain controversial. In the largest series of patients with HD managed by cervical duraplasty (CD), this study compares the outcomes between conservative and surgical management. Methods A retrospective case–control study was performed on 60 patients with HD. The cases consisted of 30 patients who underwent CD, and 30 age- and sex-matched controls who managed with long-term collar wear. Clinical improvement was recorded using two patient-reported outcome measures—the Odom's scale and a self-rated hand grip strength score. Median and ulnar compound muscle action potential (CMAP) amplitudes and various magnetic resonance imaging parameters were recorded. Results None of the controls experienced clinical improvement at follow-up; 90% remained status quo at 24.33 ± 9.38 months. Seventy-six percent of the operated patients demonstrated clinical improvement at 29.61 ± 12.78 months, and a majority of them reported moderately better grip strength. The preoperative anteroposterior diameter (APD) of the surgical group improved from 0.74 ± 0.13 to 0.86 ± 0.21 ( p = 0.01), and the cord demonstrated a significant decrease in forward migration on flexion (0.20 ± 0.11 and 0.03 ± 0.07 preoperatively and at follow-up, respectively, p < 0.0001). Patients with clinical improvement demonstrated significantly better mean APD and median and ulnar CMAP values than those who did not improve ( p < 0.0001). The mean cervical alignment did not change significantly at follow-up ( p = 0.13). Conclusions This study shows that CD can significantly alter the clinical course of patients with progressive symptoms of HD. This approach successfully arrests the forward migration of the cervical cord on flexion and promotes morphological recovery of the cord. A majority of the patients undergoing CD demonstrate clinical and electrophysiological improvement at mid-term follow-up.