Doctor Thomsen is a graduate of the University of Iowa College of Medicine and completed his dermatology training at the same university. He is Assistant Clinical Professor of Dermatology at the University of New Mexico School of Medicine and maintains a private practice at the Los Alamos Medical Center in Los Alamos, New Mexico

He is a member of the American Academy of Dermatology, New Mexico Dermatological Society, and the European Academy of Dermatology and Venereology. His interests include clinical dermatology, ethics, and the history of dermatology.