Studies say ... bipolar disorder, or even Alzheimer's. Many case reports have suggested that social media networks could exacerbate or even trigger delusional beliefs linked to erotomania.

[8] This case of delusions of parasitosis is interesting because it appears to have been induced by methampetamine use; occurred in the context of HIV; was associated with bipolar disorder ...

Case studies have shown that individuals ... Folie à Deux: A shared psychotic disorder where two individuals share the same delusional belief. This Nature Research Intelligence Topic summary ...