Guillain–Barré Syndrome Overlapping with Longitudinally Extensive Transverse Myelitis Associated with Isolated Anti-GD3 IgG Positivity

AbstractBackground/Aims: Guillain–Barré syndrome (GBS) overlapping with longitudinally extensive transverse myelitis (LETM) is a rare central–peripheral nervous system overlap syndrome. We aimed to present a patient with GBS–LETM overlap associated with isolated anti-GD3 IgG positivity and to emphasize the diagnostic value of serial electrophysiological assessment.MEthods: A 74-year-old man was evaluated by serial electrophysiological studies (days 2 and 10), cerebrospinal fluid analysis, cervicothoracic spinal magnetic resonance imaging, and serum ganglioside, nodal/paranodal, anti-myelin oligodendrocyte glycoprotein, and paraneoplastic antibody panels.Results:The patient developed rapidly progressive quadriplegia with generalized areflexia, a sensory level below T2, and urinary retention. Cerebrospinal fluid demonstrated albuminocytologic dissociation. The initial electrophysiological study showed findings compatible with early GBS, whereas the follow-up study on day 10 demonstrated marked progression to a widespread sensorimotor polyneuropathy. Cervicothoracic spinal magnetic resonance imaging revealed a longitudinally extensive T2-hyperintense intramedullary lesion extending from C3 to T1, consistent with LETM. Isolated anti-GD3 IgG positivity was detected, while other ganglioside antibodies, nodal/paranodal antibodies, anti-myelin oligodendrocyte glycoprotein antibodies, and paraneoplastic investigations were negative.Conclusion:This case highlights the possible association of isolated anti-GD3 IgG positivity with the rare GBS–LETM overlap syndrome. Furthermore, it emphasizes that limited early electrophysiological abnormalities do not exclude GBS and that serial electrophysiological assessment may facilitate diagnosis when concomitant spinal cord involvement is suspected.