Treating A Patient Who Feels There Are Parasites Under Her Skin

Tracey Vlahovic, DPM

   The workup of these patients should include: obtaining a detailed history (especially any drug abuse history and psychiatric history such as depression, bipolar disorder, etc.); ruling out a real infestation such as scabies; bloodwork (complete blood cell count with differential, electrolytes, liver function test, thyroid function, vitamin B levels); and a skin biopsy if needed. When questioning the patient, it is imperative to determine how fixed the delusion is. Most importantly, when speaking with these patients, the clinician must remain neutral and show an understanding of the patient’s predicament and stress level. Directly pointing out the delusion and/or supporting the delusion is not recommended when speaking with these patients.

   In addition to the self-induced skin injuries visualized as excoriations, ulcers and scars, patients may present with evidence of their infestation in a plastic bag or box.2 This is known as the matchbox sign. The physician may wish to examine the skin debris or clothing fibers that the patient believes is a sign of infestation under the microscope and may invite the patient to view it in order to show no evidence of parasites present. It is also important that during the physical exam, the clinician states there are no visible signs of parasites present on the skin but does so in a way that the patient does not become defensive.

Understanding The Main Differentials With Delusions Of Parasitosis

Scabies. Scabies is an intense pruritus caused by the mite Sarcoptes scabiei, var. hominis. The skin rash is characterized by red, pruritic, papulovesicular lesions and burrows. Burrows are pathognomonic and are caused by movement of the female mite in the epidermis. These can be visible on the plantar feet and interdigitally. Characteristically, the patient complains of itching that is worse at night.

   Formication. Formication describes the feeling of insects crawling on or under the skin. This can be present with diabetic neuropathy, menopause, narcotic drug use, alcohol withdrawal, as a side effect of Ritalin and Lunesta, and in patients with Lyme disease.

A Guide To The Treatment Plan

The skin biopsy in this case showed there were no reactions from an arthropod bite in the skin but it cannot definitively state the diagnosis of delusions of parasitosis. Patients are often dissatisfied with results of a skin biopsy as they will tell the clinician that it is from the wrong site since it does not show the presence of bugs. The patient was extremely fixed on the delusion that she had to create portals for the parasites to leave her skin. Upon speaking with her family members separately, they admitted to me that she had refused psychiatric care previously and I was the fifth doctor she had seen for this condition.

   During her first visit, I provided wound care to the ulcers on her legs. The patient tore off the wound dressings because she felt the parasites had no route to escape her skin. She also rejected visiting nursing care to perform dressing changes during the week. During her second and third visits, I recommended oral pimozide (Orap, Teva Biologics), a neuroleptic, to ease the itching the patient had. One would use pimozide off-label in cases of delusions of parasitosis. Pimozide has an anti-pruritic action due to its effect on opioid pathways. Other oral medications that one can use are risperidone (Risperdal Consta, Janssen Pharmaceutica) and olanzapine (Zyprexa, Eli Lilly).3

   The mainstays of treatment are consultation with the patient’s primary physician prior to starting the medication and careful monitoring of the patient once he or she is on the medication. It is important for the prescribing physician to be familiar with the side effects and the contraindications of these medications before writing for them. Side effects of these drugs include extrapyramidal syndrome, sedation, weight gain, electrocardiographic changes and anticholinergic effects.


Very interesting case Tracey. I've never seen anything like this and I've been in practice for 32 years. Thanks for sharing this very, very unusual case with your colleagues.

Vinny DiPaolo
Plainview, Texas

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