AMSAN

AMSAN, or Acute Motor and Sensory Axonal Neuropathy, is a rare variant of Guillain-Barré syndrome (GBS), an acute immune-mediated polyneuropathy. In AMSAN, the primary damage is to the axons of peripheral nerves, affecting both motor and sensory fibers, rather than the myelin sheath. This axonal involvement distinguishes AMSAN from the more common inflammatory demyelinating form of GBS.

Clinically, AMSAN presents with rapidly evolving weakness that is typically symmetric and flaccid, often accompanied by sensory disturbances such as numbness or tingling. Deep tendon reflexes are usually diminished or absent. Onset follows an infectious illness in many cases, most frequently a gastrointestinal infection, though the specific trigger varies. Respiratory muscle weakness can occur, sometimes requiring ventilatory support.

Diagnosis is based on the combination of clinical features and electrophysiological testing. Nerve conduction studies characteristically show reduced or absent motor and sensory action potentials with little or no evidence of demyelination, reflecting axonal injury. Cerebrospinal fluid may show elevated protein with few cells (albuminocytologic dissociation) but this finding can be absent early in the course. AMSAN is diagnosed when the pattern fits the clinical and electrodiagnostic criteria within the broader spectrum of GBS variants.

Treatment focuses on supportive care, including monitoring for autonomic instability and respiratory failure. Immunotherapy with intravenous immunoglobulin (IVIG) or plasmapheresis is commonly used, though responses may be slower and less complete than in some other GBS subtypes. Recovery can be prolonged, and some patients experience residual weakness or sensory deficits after the acute phase.