Clinical lycanthropy is a condition where a person believes they are able to transform into a feral beast, such as a wolf or other predator. Dr. Jan Dirk Blom studied clinical lycanthropy in 1850 and found at least 13 cases where people identified as transforming into a wolf over a 150-year period. Although rare, it was certainly enough to link them all together as a common mental illness.
And it wasn’t the first time lycanthropy was noted as a form of insanity. The condition was noted as far back as the 7th century by physician Paul of Aegina. Aegina noted some people suffered from an animalistic dissociation from humanity.