A Case of Acute Motor and Sensory Axonal Neuropathy (Amsan) Variant of Guillain-Barré Syndrome Presenting With Paradoxical Hyperreflexia and Inverted Supinator Reflex

Guillain-Barré Syndrome (GBS) encompasses a heterogeneous spectrum of acute, immune-mediated polyradiculoneuropathies, conventionally characterized by progressive, ascending flaccid paralysis, sensory disturbances, and areflexia. While the demyelinating form (AIDP) predominates in Western populations, axonal variants such as AMAN and AMSAN are increasingly recognized, particularly in Asian demographics. AMSAN is a fulminant and severe variant defined by primary axonal degeneration of both motor and sensory fibers, often associated with delayed recovery and significant residual disability. However, the presence of hyperreflexia—a sign classically attributed to Upper Motor Neuron (UMN) pathology—creates a profound diagnostic dilemma, often mimicking CNS etiologies like acute myelopathy or vasculitic neuropathy.