American Journal of Clinical Dermatology

, Volume 2, Issue 5, pp 285–290

Delusions of Parasitosis

A Dermatologist’s Guide to Diagnosis and Treatment
  • John Koo
  • Chai Sue Lee
Therapy in Practice

Abstract

Delusions of parasitosis is a rare psychiatric disorder in which the patient has a fixed, false belief that he or she is infested by parasites. Even though it is a psychiatric disorder, these patients usually present to a dermatologist because they are convinced that they have a dermatological problem. Patients with delusions of parasitosis generally reject psychiatric referral. The diagnosis of delusions of parasitosis can often be made on the basis of the history alone, but it is important to make sure that the patient does not have a organic skin disorder, and the delusion is not secondary to another mental or physical illness. The current treatment of choice is the antipsychotic medication pimozide. The principal difficulty in management is convincing patients to take the drug. This results from the obvious discrepancy between the patients’ belief system and the clinician’s understanding of the situation. The most common adverse effects of pimozide are extrapyramidal symptoms such as stiffness and, less frequently, a special inner sense of restlessness called akathisia. Effective treatment of such extrapyramidal reactions includes benztropine 1 to 2mg up to 4 times daily as needed, or diphenhydramine 25mg 3 times daily as needed. Pimozide can have cardiotoxic effects at high dosages. Traditionally, it has been recommended to check pretreatment and post-treatment electrocardiograms even for patients who have no history or cardiac conduction abnormalities or arrhythmia. However, a more recent publication questions the need for this if the patient takes <10 mg/day, is not elderly, and has no history of cardiac arrhythmia. Effective dosages of pimozide for delusions of parasitosis have ranged from 1 to 10 mg/day. The lowest effective dosage of pimozide should be used for the shortest possible duration to minimize the risk of tardive dyskinesia developing in these patients. Significant improvements in quality of life have been achieved with successful treatment with pimozide. Atypical antipsychotics such as risperidone with a much safer adverse effect profile may prove to be effective for the treatment of delusions of parasitosis in the future.

References

  1. 1.
    Johnson G.C., Anton R.F. Delusions of parasitosis: differential diagnosis and treatment. South Med J 1985; 78: 914–918PubMedCrossRefGoogle Scholar
  2. 2.
    Morris M. Delusional infestation. Br J Psychiatry 1991; 159 Suppl. 14: 83–87CrossRefGoogle Scholar
  3. 3.
    Berrios G.E. Delusional parasitosis and physical disease. Compr Psychiatry 1985; 26: 395–403PubMedCrossRefGoogle Scholar
  4. 4.
    Reilly T.M. Delusional infestation. Br J Psychiatry 1988; 153 Suppl. 2: 44–46Google Scholar
  5. 5.
    Koblenzer C.S. Psychocutaneous disease. Orlando (FL): Grune & Stratton 1987: 59–80, 108–130Google Scholar
  6. 6.
    Wilson J.W., Miller H.E. Delusions of parasitosis (acarophobia). Arch Dermatol Syph 1946; 54: 39–56CrossRefGoogle Scholar
  7. 7.
    Bishop E.R. Monosymptomatic hypochondriacal syndromes in dermatology. J Am Acad Dermatol 1983; 9: 152–158PubMedCrossRefGoogle Scholar
  8. 8.
    Wykoff R.E. Delusions of parasitosis: a review. Rev Infect Dis 1987; 9: 433–437PubMedCrossRefGoogle Scholar
  9. 9.
    May W.W., Terpenning M.S. Delusional parasitosis in geriatric patients. Psychosomatics 1991; 32: 88–94PubMedCrossRefGoogle Scholar
  10. 10.
    Munro A. Delusional parasitosis: a form of monosymptomatic hypochondriacal psychosis. Semin Dermatol 1983; 2: 197–202Google Scholar
  11. 11.
    Lyell A. Delusions of parsitosis. Br J Dermatol 1983; 108: 485–499PubMedCrossRefGoogle Scholar
  12. 12.
    Musalek M., Bach M., Passweg V., et al. The position of delusional parasitosis in psychiatric nosology and classification. Psychopathology 1990; 23: 115–124PubMedCrossRefGoogle Scholar
  13. 13.
    Retterstol N. Paranoid psychoses with hypochondriac delusions as the main delusion: a personal follow-up investigation. Acta Psychiatr Scand 1968; 44: 334–353PubMedCrossRefGoogle Scholar
  14. 14.
    Marneros A., Deister A., Rohde A. Delusional parasitosis: a comparative study to late-onset schizophrenia and organic mental disorders due to cerebral arteriosclerosis. Psychopathology 1988; 21: 267–274PubMedCrossRefGoogle Scholar
  15. 15.
    Driscoll M.S., Rothe M.J., Grant-Kels J.M., et al. Delusional parasitosis: a dermatologic, psychiatric, and pharmacologic approach. J Am Acad Dermatol 1993; 29: 1023–1033PubMedCrossRefGoogle Scholar
  16. 16.
    Lyell A. Delusions of parasitosis. Semin Dermatol 1983; 2: 189–195Google Scholar
  17. 17.
    Munro A. Monosymptomatic hypochondriacal psychosis. Br J Psychiatry 1988; 153 Suppl.: 37–40Google Scholar
  18. 18.
    Koo J. Psychodermatology. A practical manual for clinicians. Curr Probl Dermatol 1995; 7: 199–234CrossRefGoogle Scholar
  19. 19.
    Pimozide. In: McEvoy GK, editor. American hospital formulary service drug information 92. Bethesda (MD): American Society of Hospital Pharmacists, 1992: 1290-4Google Scholar
  20. 20.
    Lindskov R., Baadsgaard O. Delusions of infestation treated with pimozide: a followup study. Acta Derm Venereol Suppl (Stockh) 1985; 65: 267–270Google Scholar
  21. 21.
    Koo J.Y.M., Pham C.T. Psychodermatology: practical guidelines on pharmacotherapy. Arch Dermatol 1992; 128: 381–388PubMedCrossRefGoogle Scholar
  22. 22.
    Capellà D, Laporte J.R. Antipsychotic drugs. In: Dukes M.N.G., Aronson J.K., editors. Side effects of drugs annual 15. Amsterdam: Elsevier, 1991: 43–56Google Scholar
  23. 23.
    Schatzberg A.F., Cole J.O., DeBattista C. Manual of clinical psychopharmacology. 3rd ed. Washington, DC: APA Press, 1997: 155Google Scholar
  24. 24.
    Stahl S.M. Selecting an atypical antipsychotic by combining clinical experience with guidelines from clinical trials. J Clin Psychiatry 1999; 60 Suppl. 10: 31–41PubMedGoogle Scholar
  25. 25.
    Brown C.S., Markowitz J.S., Moore T.R., et al. Atypical antipsychotics: part II adverse effects, drug interactions and costs. Ann Pharmacother 1999; 33: 210–217PubMedCrossRefGoogle Scholar
  26. 26.
    Gallucci G., Beard G. Risperidone and the treatment of delusions of parasitosis in an elderly patient. Psychosomatics 1995 Nov–Dec; 36 (6): 578–580PubMedCrossRefGoogle Scholar

Copyright information

© Adis International Limited 2001

Authors and Affiliations

  • John Koo
    • 1
  • Chai Sue Lee
    • 1
  1. 1.Department of DermatologyUniversity of California San Francisco Medical CenterSan FranciscoUSA
  2. 2.Psoriasis Treatment CenterSan FranciscoUSA

Personalised recommendations