A Review of Delusions of Parasitosis, Part 2: Treatment Options

Treating the patient's anxiety should be seriously considered.6 Benzodiazepines such as diazepam and alprazolam are commonly used for short-term treatment of anxiety. These medications are fast acting and can be withdrawn after a few weeks. Consultation with a psychiatrist can be helpful for clinicians who are not familiar or comfortable with these drugs. Treating the symptomatic itching or burning sensation experienced by many patients also should be considered. Crotamiton cream is useful for pruritus and possibly eradicates some organisms. Topical or intramuscular corticosteroids may be useful to alleviate the itching sensation. Additionally, an antihistamine can be useful. Over-the-counter anti-itch medications also can be used.

Treating the Delusion
Until the 1950s, DOP was considered a nontreatable disease. In 1946, Wilson and Miller11 reported that beyond treating the patient for syphilis, if indicated, "there is nothing whatsoever the dermatologist can do for such a patient." While viable treatment options are now available, management remains a challenge for clinicians, especially nonpsychiatrists. A meta-analysis of 1223 case reports of DOP showed marked improvement in full remission rates from the prepsychopharmacologic era (before 1960) to the postpsychopharmacologic era (after 1960)(33.9% to 51.9%, respectively).12 Most cases of DOP need to be treated. There have been few reported cases of spontaneous remission of DOP.13,14 Most experts will agree that referral to a psychiatrist is beneficial. It is debatable if psychiatrists are the only clinicians equipped to handle these patients or if dermatologists may and should prescribe pimozide.15,16 Koblenzer17 stated: "If not treated by the dermatologist, [patients with DOP are] doomed to a prolonged, expensive, and frenetic search from doctor to doctor, to exterminator, to entomologist, and so on, without relief." Regardless of the medication used, the clinician must proceed with caution when suggesting treatment to patients with DOP. Commonly, when a clinician suggests psychiatric referral or medication, the patient responds angrily and does not return.5,18 Patients can become a danger to themselves and others. One man set fire to one of his apartments and flooded another19; other patients have committed suicide.13,20 It is important to note the extreme desperation in which these patients often find themselves. Many patients have tried relentlessly to find a treatment for their supposed infestation and often have found their clinician to be more of a hindrance than a help. One such case resulted in an attempt on the life of a family physician.21

Pimozide
Pimozide is approved by the US Food and Drug Administration for Tourette syndrome. It was first used in 1975 to treat somatic delusions, as reported in 5 patients.22 Since then, this neuroleptic agent has been considered the treatment of choice for DOP. Pimozide is a highly selective dopamine D2 blocker; thus, it is effective in treating psychoses. Pimozide also has some serotonin receptor blocking activity, which is theorized to contribute to its therapeutic effects. Other neurologic effects include blockade of a-adrenergic receptor sites, voltage-gated calcium channels, and opiate receptors. Pimozide has approximately 50% oral bioavailability and its action lasts 24 to 48 hours, allowing for once-daily dosing. It is metabolized in the liver and primarily excreted in the urine.23 The most common side effects of pimozide are extrapyramidal symptoms, including pseudoparkinsonism, akathisia, and dystonia. Pseudoparkinsonism may manifest as muscle and joint stiffness, while akathisia is indicated by restlessness. These effects have been demonstrated in patients treated with a pimozide dosage as low as 2 mg daily.24 Symptoms can be controlled by anticholinergic medications, such as oral benztropine mesylate 1 to 4 mg once or twice daily, as needed, or diphenhydramine hydrochloride 25 mg 4 times daily, as needed. Benztropine mesylate is preferred versus diphenhydramine hydrochloride because it is not sedating. An acute dystonic reaction (ie, muscle spasm) rarely occurs because of the low dose of neuroleptic prescribed; however, the acute reaction also responds to anticholinergic agents.16 To minimize the risk for side effects, initially prescribe pimozide 1 mg daily, titrating up by 1 mg every 5 to 7 days (maximum, 10 mg daily), as needed. Koo and Lee25 recommend using the lowest effective dose of pimozide for the shortest possible duration. Pimozide at high doses has cardiotoxic properties manifested by long QT intervals and arrhythmias. Pretreatment and posttreatment electrocardiograms are recommended for all patients receiving pimozide.26 Discontinue increasing the dose when the QT interval is more than 0.52 seconds in adults or when there is a QT interval increase of 25% or more above the patient's baseline.27 Furthermore, coadministration of other drugs that increase the QT interval should be avoided, including but not limited to chlorpromazine, gatifloxacin, mefloquine, moxifloxacin hydrochloride, other class Ia and III antiarrhythmic agents, quinidine, tacrolimus, thioridazine hydrochloride, and ziprasidone hydrochloride or mesylate.28 Pimozide is the most studied and reported drug used for DOP. Most data on pimozide have come from individual or group case reports, though 2 double-blind placebo-controlled trials have been conducted. Of the 189 patients reported to be treated with pimozide in 22 articles, 79% reported a positive response to pimozide, 17% reported no response, and the rest were lost to follow-up.8,13,24,26,29-46 Side effects reported with pimozide included insomnia, drowsiness, and depression.34,41 Extrapyramidal symptoms such as pseudoparkinsonism and akathisia were not uncommon but generally were easily controlled with anticholinergic agents.13,24,26,34,35,38,40,41,45 Two cases of lethargy were reported with pimozide doses of up to 6 to 24 mg daily.41 An acute dystonic reaction occurred in a patient receiving 8 mg daily.40 The mean dosage of pimozide used for best effect was 5 mg daily, as per the case series for which this information was available.8,13,24,26,29-46 Both single and split dosing were reported as successful methods. The median duration of treatment to best results was 3.5 weeks, with a range of 3 days to 6 months. For patients who were followed long-term (4–12 mo), 100% (n=17) maintained complete or near complete resolution of symptoms (near complete in 1 patient) while receiving maintenance doses of pimozide. Daily doses ranged from 2 to 4 mg. For patients followed long-term who eventually discontinued pimozide, 43% (34/79) had subsequent recurrence of their symptoms. Of those patients re-treated with pimozide, 100% (n=20) had complete resolution of symptoms.8,13,24,26,29-46 Zomer et al46 studied 33 patients with DOP. A total of 61.1% (11/18) of patients reported improvement or full recovery with pimozide compared with the 20% (3/15) not treated. At a mean follow-up of 5 years, none of the patients who had full remission (5/33 with DOP) needed maintenance therapy.46 Hamann and Avnstorp34 conducted a double-blind, placebo-controlled, crossover trial in which participants showed a significant response to pimozide compared with placebo (P