How do you treat this problem?

Delusions, like hallucinations, are psychotic symptoms that are theorized to result from increased levels of dopamine in parts of the brain. Patients with delusions of parasitosis have been shown to respond to neuroleptics; in particular, the dopamine antagonist pimozide (Orap) is, historically, the commonly used treatment. However, more recent anecdotal success has been reported with other agents having fewer side effects, including risperidone, olanzapine, and escitalopram. Although, large, well-controlled, randomized trials comparing the efficacy of these drugs are lacking, these drugs are now probably the drugs of choice.

Fellner MJ, Majeed MH: Tales of bugs, delusions of parasitosis, and what to do, Clin Dermatol 27:135–136, 2009.