Successful Treatment of Delusional Infestation with Olanzapine Depot.

Delusional infestation (DI) is a rare psychiatric disorder characterized by a persistent false belief that one is infected with nonliving or living pathogens, usually accompanied by formication. Other psychotic features, such as disorganized speech or hallucinations unrelated to the core delusion itself, are never present, and the delusional belief does not extend into other areas of life. Secondary DI, when one needs to address the underlying condition in order to achieve adequate treatment, is also possible. We present the case of a 42-year-old male with a 2-year history of having a persistent and firm belief that his house was infested with tiny insects that were constantly biting him and laying their eggs under his skin. His delusional belief was preceded by a complex, years-long substance use disorder, which confronted us with a differential diagnostic dilemma between primary and secondary DI. He was successfully treated with olanzapine pamoate depot, which was introduced to address his lack of insight and unsatisfactory compliance, and his delusion faded away after his symptoms subsided.