[A recalcitrant case of encephalitis with voltage-gated potassium channel antibodies].

We report the case of a 65-year-old man who had encephalitis with a high titer of voltage-gated potassium channel antibodies (VGKC-Abs). His initial symptoms included memory disturbance, confusion, and seizures. Laboratory tests revealed a low plasma sodium concentration and a strong positive result for VGKC-Abs. A diffusion-weighted magnetic resonance imaging (MRI) scan showed a high intensity lesion within the right basal ganglia, which later showed normal intensity. The patient's initial symptoms resolved without any treatment. During the first relapse, the patient experienced consciousness disturbance and an increased number of seizures than that observed initially. A diffusion weighted MRI scan showed a high intensity lesion within the right hippocampus, and a fluid attenuated inversion recovery (FLAIR) weighted MRI scan showed high intensity lesions within the right hippocampus, right thalamus, and pons. The patient's symptoms and the MRI abnormalities resolved with prednisolone therapy. During the second relapse, he again experienced consciousness disturbance and an increased number of seizures than that observed initially. Diffusion-and FLAIR weighted MRI scans showed high intensity lesions within the right thalamus. However, the array of immunosuppressive treatments used during the first relapse was not as effective during the second relapse. The serum VGKC-Ab titers before steroid therapy during the first relapse and after immunosuppressive treatment during the second relapse were 1,252 pmol/L and 22.4 pmol/L, respectively. Brain MRI revealed signal changes in the basal ganglia at the onset of disease, in the limbic area during the first relapse, and in the thalamus during the second relapse. VGKC-Ab-associated encephalopathy is usually considered a benign autoimmune disorder; however, in our case, the encephalitis gradually became intractable to various immunosuppressive treatments, and unique MRI abnormalities were observed.