Antibodies to voltage-gated potassium channels (VGKC) are associated with acquired neuromyotonia, limbic encephalitis, and Morvan's syndrome. The antibodies are often not associated with malignancy and have shown good clinical response to immunomodulatory therapies. A record review identified five patients with laboratory evidence of antibodies to VGKC who underwent plasma exchange (PE) as part of their immunosuppressive therapy for neurologic disease. Four of the patients presented with limbic encephalitis and one with neuromyotonia. Symptoms included memory impairment, seizures, and personality changes. All PE were 1.0 volume and were performed on an every-other-day schedule. Replacement fluid was 5% normal serum albumin except when a bleeding risk was identified and then fresh frozen plasma was added. Four of five patients were also receiving concurrent immunosuppressive therapy including corticosteroids. Of the five patients treated with PE, three had sustained improvement in symptoms for 6-17 months following PE. Two patients did not have signs of improvement at a limited follow-up. One patient had recurrence of her symptoms, which responded to additional PE. These cases, as well as the reports in the literature, suggest that PE could be a useful adjunctive therapy for patients with VGKC antibodies and neurologic symptoms.
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