Hyperacute Guillain-Barré Syndrome Reaching Clinical Nadir Within 16 Hours.

A 36-year-old man presented with rapidly progressive lower-limb weakness that reached its nadir within 16 h of the onset. The initial nerve conduction study (NCS) revealed no significant abnormalities except for a decrease in F-waves. Intravenous immunoglobulin therapy was administered, resulting in a gradual improvement in muscle strength. Follow-up NCS revealed findings consistent with axonal damage, and subsequent testing revealed positivity for immunoglobulin G-class anti-GM1 antibodies. The patient was finally diagnosed with acute motor axonal neuropathy, a variant of Guillain-Barré syndrome (GBS). This case highlights the importance of considering GBS even in patients with hyperacute progression to nadir within 24 h.