Delusional disorder, which used to be called paranoia, is one of the schizophrenia spectrum conditions. In contrast to schizophrenia, however, patients with delusional disorder only experience prominent delusions and no or only minimal formal thought disorder, negative symptoms or neurocognitive deficits. Usually, one delusional theme that is potentially plausible (albeit unlikely) dominates. Persecutory and grandiose delusions are common but somatic and jealous delusions are also frequently encountered. If patients have hallucinations, they are related to the theme of the delusions. Patients who fear persecution may smell gas in their apartment for example. The entrenched nature of the delusion can lead to significant functional impairment despite the paucity of other psychopathological findings.
Patients with delusional disorder will rarely seek help from a psychiatrist due to limited insight into their predicament and strong delusional conviction. Depending on the delusional theme, they may seek help from a medical specialist (e.g., see a dermatologist for delusional infestation) but resist a subsequent referral to psychiatry.
The treatment of delusional disorder is notoriously challenging. The challenge does not necessarily lie in the refractory nature of symptoms to antipsychotic treatment per se but in the categorical rejection of psychiatric treatment. A long period of engagement is sometimes successful. Some patients may agree to an antipsychotic trial to manage the unpleasant affect and suffering that are the results of “not being believed” or the anxiety and fear that accompanies the psychotic experience. Other psychotropics like antidepressants or benzodiazepines to reduce the affective component can be offered symptomatically.
The efficacy of antipsychotics may be comparable to schizophrenia and underestimated given the psychological resistance to treatment. While pimozide has gotten the reputation of being particularly effective for delusional disorder, any antipsychotic, if taken, may work just as well although no comparative studies have been conducted. Pimozide is a dopamine-2 blocker but also a potent calcium channel blocker that can cause QTc prolongation and hypotension. Cognitive-behavioral therapy, if accepted, can be tried but there are no well-conducted studies that support its benefit. All treatment recommendations are based on case reports and case series as this rare condition has been difficult to study.