Association of the Achondroplasia Foramen Magnum Score and intraoperative neuromonitoring

Introduction Foramen magnum stenosis in achondroplasia carries a risk of sudden death. A proportion of these patients benefit from foramen magnum decompression (FMD). The Achondroplasia Foramen Magnum Score (AFMS) was developed to stratify those most at risk. We hypothesise that this score may be reflected in neurophysiological findings.Methods Patients with achondroplasia who had undergone FMD (n=20) were retrospectively grouped into AFMS 2, 3 and 4. Amplitude from tibialis anterior (TA) and the percentage change in somatosensory evoked potential (SSEP) latency after FMD were reported.Results Baseline motor evoked potential amplitudes for patients with AFMS=4 were significantly lower left (p=0.0017 and p=0.02 for right and left TA, respectively) compared with AFMS grades 2 and 3. Median reduction (% change) in SSEP latency (ms) after surgery was not significantly different in any of the patients.Conclusions This short report cross-references AFMS to intraoperative neuromonitoring. Baseline amplitudes were noticeably lower in the most severe AFMS group. This observation supports the notion that AFMS can help risk stratify patients and aid in surgical selection.