**Key Results:**
- **Epidemiology:** Prevalence and incidence vary by region. In the US, initial studies reported rates of 1–1.9 per 100,000 person-years, with an average age at diagnosis of 61. A study in central California found a prevalence of 3.7 per 100,000, average age 52, and >75% female. In Europe, British researchers reported annual incidence rates of 2–2.37 and 17 per 1 million inhabitants per year; prevalence is estimated at around 80 cases per million. In India, prevalence was 19 out of 4200 patients, with increased incidence after age 40. Recent data suggest a general incidence of 1.9–3.7 cases/100,000 subject-years and prevalence of 27.3/100,000 subject-years.
- **Pathophysiology:** The leading theory involves dopaminergic system imbalances. DAT dysfunction leads to increased extracellular striatal dopamine, causing disturbances in perception and thinking. Age-related decline in DAT density and estrogen's neuroprotective role may contribute. Antipsychotics block D2/D3 receptors to reduce symptomatology.
- **Risk Factors:** Include female gender, old age, social isolation, stressful lifestyle, divorce, and substance abuse (especially cocaine, amphetamines, methamphetamine). Secondary DP can be triggered by medications such as corticosteroids, opiates, benzodiazepines, ketoconazole, fluoroquinolones, topiramate, pramipexole, and ropinirole.
- **Clinical Aspects:** Classic profile is elderly women with paranoid or obsessive-compulsive traits. Main symptoms are delusions of infestation and tactile hallucinations ("biting", "crawling"). The "matchbox sign" (bringing specimens) is pathognomonic. DP can be episodic or chronic, with an average duration of 3 years. More than half of patients have a history of depression.
- **Diagnosis:** DP is classified under Delusional Disorder, somatic subtype in DSM-5 (code F22.8 in ICD-10). Diagnosis requires conviction of infestation despite evidence and abnormal cutaneous sensations. Paraclinical tests include full blood count, ESR, CRP, liver function, TSH, creatinine, fasting glucose, urine drug tests, serology for borrelia, treponema, hepatitis, HIV, vitamin B12 and folate levels, and skin biopsy if indicated. Neuroimaging may show wider right medial orbito-frontal gyrus cortical thickness and reduced surface area in temporoparietal regions.
- **Differential Diagnosis:** Includes formication (without delusions), cocaine bugs, genuine parasitosis (scabies, pet-induced dermatitis), and other psychiatric conditions.
- **Therapeutic Management:** Antipsychotics are first-line. First-generation: pimozide (1–12 mg/day, full remission 48%, partial 52%), haloperidol (1–10 mg/day, full remission 66.6%, partial 33.3%), trifluoperazine (2–15 mg/day, full remission 43%, partial 43%, no effect 14%). Second-generation: risperidone (0.5–3 mg/day, full remission at 0.5–1 mg, partial at 1–3 mg), quetiapine (50–300 mg/day, partial remission), olanzapine (2.5–10 mg/day, partial remission). Aripiprazole may be preferred in elderly or those with cardiac issues, depression, or anxiety. Treatment should start low and go slow, with evaluation every 4 weeks. After improvement, medication is continued for 3–6 months. For resistant cases, combination with SSRIs (e.g., fluoxetine) or electroconvulsive therapy with clozapine may be considered. Long-acting injectables are reserved for non-compliant patients but are not advised in elderly due to risk of neuroleptic malignant syndrome.
- **Associated Conditions:** Folie à deux occurs in 5–15% of DP cases. Morgellons disease is considered part of delusional infestation. DP can be associated with Parkinson's disease (as side effect of antiparkinsonian treatment or prodromal symptom), dementia (prevalence ~5%), substance use (cocaine, amphetamines, alcohol), stroke (especially right-side lesions), COVID-19 (post-infectious), and drug-induced DP (anti-Parkinson medications, antidepressants, antiepileptics, stimulants).