Reversible Cerebral Vasoconstriction Syndrome and Varicella Zoster Virus

Among patients with thunderclap headache who were admitted to the four participating hospitals, who has diffuse segmental vasoconstriction on CT angiography or MR angiography will be eligible for the study. Participants who meet the definition of RCVS will be enrolled as the case-patients and others will be enrolled as control-patients. The RCVS group will be defined when two or more neurologists agree by the clinical features and angiographic findings. The result of tests for varicella zoster virus titer will not be opened to neurologists until the end of the study. For case and control patients, tests for varicella zoster virus infection are (1) Pre-existing virological markers (ex. VZV-IgG, IgM, and VZV PCR in CSF or Skin lesion if present) (2) VZV-specific cell mediated immune response (CMI) at the time of admission and one month later (3) VZV in blood measured by quantitative test of viral load with real-time PCR and digital PCR for latent viral load (4) Quantitative test of viral load with real-time PCR in saliva at time of admission and one month later. Reactivation or infection of VZV of patients with RCVS and controls will be compared.