Blink reflex role in algorithmic genetic testing of inherited polyneuropathies

Introduction: In severely affected inherited polyneuropathy patients, primary demyelination can be difficult to determine by routine extremity limb nerve conduction studies (NCS). Blink reflexes may help classify severe polyneuropathies as either axonal or demyelinating. However, blink reflex studies have not been studied systematically in any genetically confirmed cohort. Methods: Patients with a genetic diagnosis who had undergone blink reflex testing and extremity NCS were identified retrospectively. Blink reflex R1 latency, extremity NCS, and severity were compared. Results: We identified 26 demyelinating and 23 axonal, genetically confirmed cases, including 20 with PMP22 duplications. In 12 (25%), the ulnar CMAP amplitude was ≤0.5 mV making electrophysiological classification difficult. However, the R1-latency cutoff of >13 ms (demyelinating) robustly classified all patients regardless of severity. Conclusions: We show that blink reflex studies are reliable for identification of inherited demyelinating polyneuropathy regardless of severity and can facilitate algorithmic decisions in genetic testing. Muscle Nerve 55: 316–322, 2017.