Hyperventilation-induced focal seizures in adults: think autoimmune encephalitis.

Case reports have described rare patients with autoimmune encephalitis in whom focal seizures could be reliably provoked by hyperventilation. With the hypothesis that this phenomenon may have diagnostic significance, all cases of hyperventilation-induced focal seizures identified during ~10,000 consecutive routine electroencephalography (EEG) studies were reviewed, and corresponding diagnoses established. Seven EEG recordings, in six patients, contained focal hyperventilation-induced seizures, each of temporal lobe onset. All patients were diagnosed with autoimmune encephalitis, in two cases after EEG; five had voltage-gated potassium channel complex autoantibodies. Although rare, a hyperventilation-induced focal seizure during EEG in an adult should raise concern for autoimmune encephalitis.