Waves in Extremities: A Rare Report of Isolated Isaacs' Syndrome

Isaacs' syndrome is a rare neuromuscular hyperexcitable syndrome with myriad manifestations ranging from motor and sensory to autonomic presentations, leading to diagnostic challenges. Among the commonest forms, a tetrad of stiffness, myokymia (muscle twitching at rest), weakness, and psuedomyotonia (delayed muscle relaxation) is almost always present. Herein, we report a case of a 16-year-old male who presented to the neurology consult service with intense wave-like pain in the lower extremities with desquamating rash and cold-induced allodynia. Investigations were significant for raised CK levels, positive autoimmune panel, and anti-voltage-gated potassium channel (anti-VGKC) antibody that is involved in 35% reported cases of Isaacs' syndrome, with electrodiagnostic studies peculiar for Isaacs syndrome with negative imaging results. He was followed up on a long cocktail course of immunosuppressive, anticonvulsive medications, and immunoadsorption plasmapheresis (IAP) for 11 months with complete remission.