What is the treatment for delusional parasitosis?

Treatment of Delusional Parasitosis

Antipsychotic medication is the primary treatment for delusional parasitosis, with pimozide historically considered first-line and atypical antipsychotics like risperidone increasingly preferred due to superior safety profiles. 1, 2

Diagnostic Confirmation Before Treatment

• Rule out actual parasitic infestation through thorough skin examination and laboratory testing before initiating psychiatric treatment 1
• Screen for secondary causes including depression, anxiety, substance abuse, neurological conditions (dementia, stroke, Parkinson's disease), and medical causes (thyroid disease, vitamin deficiencies) that can produce delusional symptoms 1, 3
• Recognize that 50% of patients with underlying depression may achieve full remission when the depression is treated with antidepressants rather than antipsychotics alone 3

Establishing Therapeutic Alliance

• Maintain continuity with the same dermatologist to build the trust essential for medication adherence 1
• Frame antipsychotic medication as treatment for physical sensations (crawling, biting, pruritus) rather than as psychiatric treatment to increase patient acceptance 1
• Avoid psychiatric referral initially, as patients with delusional parasitosis typically reject this approach 2, 4

First-Line Pharmacological Treatment

Atypical Antipsychotics (Preferred)

• Risperidone is recommended as first-line, particularly in elderly patients or those with cardiac risk factors 1, 2
• Start risperidone at 0.5 mg orally daily, with dose reduction in older patients and those with renal or hepatic impairment 5
• Alternative atypical antipsychotics include quetiapine (starting 25 mg) or olanzapine (starting 2.5-5 mg) 6, 5
• Aripiprazole may offer benefits with fewer metabolic side effects 6, 5

Pimozide (Traditional First-Line)

• Effective dosages range from 1-10 mg/day, with most patients responding to lower doses 2, 7
• Allow 4-6 weeks before determining efficacy, as antipsychotic effects typically become apparent after 1-2 weeks 1
• Use the lowest effective dose for the shortest duration to minimize risk of tardive dyskinesia 2
• Monitor for extrapyramidal symptoms (stiffness, akathisia) which can be managed with benztropine 1-2 mg up to 4 times daily or diphenhydramine 25 mg three times daily 2
• Cardiotoxic effects occur at high dosages; ECG monitoring is traditionally recommended, though may not be necessary if dose <10 mg/day in non-elderly patients without cardiac history 2

Treatment Duration and Monitoring

• Most treated patients (68%) report improvement or resolution of symptoms with pharmacological therapy 8
• Prolonged treatment is often required: 73% of patients who completed treatment achieved remission for at least 9 months, but 27% relapsed within 4 months of stopping 8
• Recurrence risk is highest in the first few months after discontinuation, necessitating longer treatment courses or maintenance therapy 8
• Evaluate response within 30 days; refer to mental health professional if minimal or no improvement 6

Management of Shared Psychotic Disorder

• Up to 15% of cases involve folie à deux (shared psychotic disorder) where family members experience the same delusion 1, 4
• Include families in the treatment plan and provide emotional support and practical advice 1, 5

Collaborative Care Model

• Close collaboration among dermatologists, psychiatrists, and parasitologists is essential for diagnosis and treatment 1, 4
• Dermatologists should play the primary role in prescribing antipsychotics after consulting a liaison psychiatrist 1, 7

Critical Pitfalls to Avoid

• Never miss secondary causes (substance abuse, medications, neurological disease, genuine parasitic infestation) before diagnosing primary delusional parasitosis 1, 3
• Do not use excessive antipsychotic doses, as this increases side effects without improving efficacy 1
• Avoid abrupt discontinuation of successful treatment, as relapse rates are high; consider gradual tapering or maintenance therapy 8
• Do not immediately refer to psychiatry, as patients typically refuse psychiatric care and this approach undermines the therapeutic relationship 2, 4
• Recognize that patients with organic brain syndromes have significantly worse outcomes due to lack of effective psychopharmacological treatment options 3