Rochester, Minnesota


Klaas.James@mayo.edu Clinical Profile


James P. Klaas, M.D., is the lead neurologist for the comprehensive and multidisciplinary moyamoya program at Mayo Clinic in Rochester, Minnesota. His research focuses on diagnostic testing and advanced imaging techniques to effectively diagnose moyamoya disease, rule out other conditions that can mimic it and determine the best intervention.

Moyamoya disease is a rare, complex and incompletely understood cerebrovascular disorder. It was first described in Japan in the late 1950s and remains more common in East Asian countries, although it affects people all over the world. In patients with moyamoya disease, the carotid artery in the skull becomes blocked or narrowed, reducing blood flow to the brain and prompting tiny blood vessels to develop at the base of the brain in an attempt to supply the brain with enough blood.

Once diagnosed, the goal is to predict which patients are at risk of complications — such as stroke, seizure or cognitive impairment — and to intervene to prevent these complications. Definitive treatment for moyamoya disease usually involves a bypass surgery. Dr. Klaas' research using advanced imaging can help clinicians decide if a patient is a candidate for — and would benefit from — bypass surgery and determine the ideal timing of such an intervention.

Focus areas

  • Natural history and etiology of moyamoya disease, especially in a North American population
  • Advanced imaging techniques for improving diagnosis of moyamoya disease, determining cerebrovascular reserve, and confirming candidacy and timing for bypass surgery
  • Extracranial and systemic manifestations of moyamoya disease

Significance to patient care

Accurate diagnosis is crucial, and there are numerous conditions that can mimic moyamoya disease that require different treatments altogether. By further elucidating the natural history and cause of moyamoya disease in a North American cohort, Dr. Klaas hopes to help better patients' knowledge and develop individually tailored, novel and improved treatment recommendations and strategies.

The goal of Dr. Klaas' research is to further elucidate the cause of moyamoya disease, especially in the North American population, and improve diagnostic and imaging evaluations, treatment strategies and clinical outcomes.


Primary Appointment

  1. Consultant, Department of Neurology
  2. Chair of Practice Operations, Adult Neurology, Department of Neurology

Administrative Appointment

  1. Associate Chair, E-Health, Department of Neurology

Academic Rank

  1. Assistant Professor of Neurology


  1. Fellow Stroke/Cerebrovascular, Programs in Rochester, Mayo School of Graduate Medical Education, Mayo Clinic College of Medicine
  2. Residency - Neurology Mayo Clinic, Mayo Graduate School of Medicine
  3. Resident Neurology, Programs in Rochester, Mayo School of Graduate Medical Education, Mayo Clinic College of Medicine
  4. Internship - Internal medicine Mayo Clinic, Mayo Graduate School of Medicine
  5. Resident Preliminary Internal Medicine, Programs in Rochester, Mayo School of Graduate Medical Education, Mayo Clinic College of Medicine
  6. MD University of Minnesota
  7. BA - Biology-Genetics Dartmouth College

Clinical Studies

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