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Chapter 95: Delusions of Parasitosis

Marwa Hakimi; John Koo

DELUSIONS OF PARASITOSIS

Therapeutic Approach

Delusions of parasitosis (DOP) is a psychiatric disorder characterized by a fixed, false belief that there is an infestation in the skin. This is the most common type of monosymptomatic hypochondriacal psychosis. Patients experience cutaneous dysesthesias that may be perceived as an organism (DOP), or a foreign body (Morgellons disease). While primary DOP occurs spontaneously, secondary DOP is a symptom resulting from varied causes including illicit drug use, underlying medical or psychiatric disorders, organic brain disease, etc. The management strategy for secondary DOP is referral to other specialties, mainly psychiatry. For primary DOP patients that are not amenable to a mental health referral, antipsychotics are the most effective treatment. It can be explained to patients that medications that are utilized in one condition can often have additional unrelated uses. A strong therapeutic relationship is key to this management. Currently there are no FDA-approved therapies, and no one antipsychotic has been shown to be conclusively more effective than another. Thus, treatment can be selected based on antipsychotic side effect profile. Therapy should be initiated at a low dose as patients with DOP often respond to lower doses of antipsychotics than patients with other psychotic disorders, and then gradually increase every 2-4 weeks until the lowest effective daily dose is achieved. The antipsychotic should be maintained for several months beyond when complete or near complete symptom control is achieved before initiating a gradual taper. Therapy should also include treatment of secondary skin damage. See Table 95-1.

Table 95-1Delusions of Parasitosis Treatment Table
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Table 95-1 Delusions of Parasitosis Treatment Table
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MEDICATION NAME INDICATION MECHANISM OF ACTION DOSING ADVERSE EFFECTSb SUGGESTIVE MONITORING LEVEL OF EVIDENCE (REFERENCE)
Topical Therapy
Creams with camphor, menthol or pramoxine Secondary skin damage; pruritus/dysesthesias Camphor: analgesic producing warm sensation by exciting and desensitizing sensory nerves; menthol: cooling sensation by stimulating nociceptors and then desensitizing them; pramoxine: local anesthetic that binds and inhibits voltage-gated sodium channels stopping action potential propagation Camphor 3%-11% ointment TID; menthol 0.5% cream/lotion, 1% powder, apply QD; pramoxine 1% cream or lotion TID Skin irritation None IV1
Occlusive dressings Secondary skin damage Limiting access to involved parts of the skin — — None IV
Systemic Therapy
Pimozide Delusional ideation Blockade of dopamine receptors and antagonistic effects on opiate receptors 0.5-12 mg QD Extrapyramidal symptoms (dystonia, pseudoparkinsonism, akathisa, tardive dyskinesia), QTc prolongation, drug-drug interactionsa Pretreatment BMP, Mg, and EKG and periodically thereafter during dosage adjustment IB1-3
Risperidone Delusional ideation D2 and serotonin type 2 (5HT2) receptor antagonism 0.5-8 mg QD Prolactin elevation Baseline blood pressure, lipid panel, fasting plasma glucose, BMI, waist circumference IV4-8
Olanzapine Delusional ideation Antagonism of serotonin 5-HT2A and 5-HT2C, dopamine D1-4, histamine H1, and alpha1-adrenergic receptors 2.5-20 mg QD Weight gain, glucose abnormalities, dyslipidemia, sedation

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