Pan-Neurofascin Antibody-Associated Nodopathy: A Critical Guillain-Barré Syndrome Mimic in the Differential Diagnosis-Report of Two Cases.

Guillain-Barré syndrome (GBS) is an acute autoimmune polyradiculoneuropathy typically characterized by an ascending sensorimotor deficit with potential involvement of bulbar and respiratory muscles that may necessitate intensive care admission and mechanical ventilation. Standard treatment includes supportive care, management of complications such as weakness, immobility, respiratory failure, autonomic dysfunction and pain, along with early initiation of immunotherapy-either intravenous immunoglobulin (IVIg) or plasma exchange (PE). However, lack of significant clinical improvement following immunotherapy should prompt consideration of alternative diagnoses, including pan-neurofascin antibody-positive autoimmune nodopathy (panNF + AN). In this report, we present two patients presenting with a severe GBS-like neuropathy. Initial treatment with IVIg resulted in either no response or only transient, mild improvement, followed by rapid clinical deterioration to near-complete tetraplegia, respiratory failure, and autonomic and cranial nerve involvement. Both patients were unresponsive to further treatment with a second course of IVIg, PE and corticosteroids. Subsequent diagnostic evaluation revealed the presence of pan-neurofascin antibodies, confirming panNF + AN. This prompted initiation of treatment with rituximab, which resulted in sustained and complete clinical recovery in both cases. A transient or mild clinical response-or an initial lack of response-to standard GBS-treatment followed by rapid and severe deterioration in cases initially presenting as GBS should be considered a red flag warranting evaluation for AN-associated antibodies. Recognition of this important GBS mimic is critical, as it requires an alternative treatment approach with rituximab, which has been associated excellent clinical outcomes.