And that’s where Mr. A’s tale grows strange: He became convinced that, any time he was contacted by other women on Facebook, they were really that same woman who had originally spurned him. She was just disguising herself, he figured. Indeed, he grew to believe she was applying the same type of facial cream that he used, which allowed her to transform her face. In these new disguises, the woman was now pursuing him.

And so, despite her earlier withdrawal, Mr. A became convinced the woman was still interested in a relationship — just in the form of different people.

At the psychiatric outpatient service, Mr. A showed no abnormalities in his neurological assessments, which included brain scans like a cerebral MRI. After ruling out brain lesions and other problems, doctors diagnosed him with Fregoli syndrome, which falls into a category of conditions known as delusional misidentification syndromes. People with Fregoli syndrome believe that some strangers they meet are actually people they know in disguise. In some ways, it’s the reverse of a better-known condition known as Capgras syndrome, which is when people believe family members or others close to them have been replaced by impostors.