Treating A Patient Who Feels There Are Parasites Under Her Skin

Pages: 28 - 33
Tracey Vlahovic, DPM

A 54-year-old woman presents with bilateral leg lesions that are pruritic and bothersome, a condition that is several years in duration. She has seen several physicians for this condition but “no one seems to be able to help” her. As she is sitting in the treatment chair, the patient actively scratches her legs and forearms. She says there is something “underneath” and she must “get it out.” She denies that the itching gets worse at night but notes that it bothers her throughout the day.

   The patient has no other pertinent past medical history, no allergies and no current medications. She denies fever, chills and joint pain. She is not currently using any topical medications on the areas. She denies having any pets at home, traveling or being around animals recently. She presents with two other family members who live with her and are not experiencing any itching themselves.

   The physical exam reveals excoriations, ulcerations, hypopigmented patches and hyperpigmented areas surrounding the ulcerations on the lower legs. There are healed areas with no active ulceration. In addition, the patient has similar lesions on the forearms and admits to scratching the upper thigh area. I sent a skin biopsy for histopathology.

Key Questions To Consider

1. What are the characteristic skin lesions in this disease?
2. What is the most likely diagnosis?
3. What is your differential diagnosis?
4. What are the characteristic lesions with this condition?
5. What is the treatment?

Answering The Key Diagnostic Questions

1. The characteristics most associated with this skin condition are self-induced lesions that may appear as erosions, ulcerations, prurigo nodularis or no skin lesions at all. Patients will typically scratch the areas in easy reach with their dominant hand. They will collect clothing fibers and skin debris in containers (the “matchbox sign”) as evidence of the insects they believe are living under their skin.
2. The most likely diagnosis is delusions of parasitosis.
3. Differential diagnoses include: scabies, formication, internal malignancy and nutritional disorders (like pellagra).
4. The characteristic lesions with this condition can range from an absence of skin injury to excoriations and ulcers that may or may not have crusted over.
5. Treatment includes the drug of choice pimozide, empathy from the treating physician and an eventual psychiatric consult and team approach.

What You Should Know About Delusions of Parasitosis

This patient has delusions of parasitosis. Biopsy results did not reveal evidence of an arthropod bite reaction. However, the patient’s insistence that bugs were crawling under her skin and she needed to create a portal to let them out were indicators that either a real infestation or a delusion was happening. Delusions of parasitosis is a firmly fixed delusional disorder in which the patient firmly believes there are parasites under the skin.1 Patients will often present to a dermatologist or primary care physician, and will frequently refuse psychiatric consultation. The cause of delusions of parasitosis is unknown.

   These patients will often present in an agitated, defensive state to the attending physician and can be described as “doctor shoppers” as they have seen numerous clinicians for this without the result they want (i.e. finding the parasites in the skin). If someone in the patient’s immediate circle of family or friends shares this delusion with the patient, the term for this is “folie à deux.”

   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.

   Consider the risk/benefit ratio for these patients in order to improve their quality of life. For pimozide alone, the full remission rates have ranged from 33 to 90 percent. However, it is a challenge to have the patient agree to this therapy and it takes patience and empathy on the part of the treating physician. Encouraging the patient to shift his or her focus from the “infestation” to the suffering he or she is experiencing is a place to begin the pharmacologic management conversation.

   In the past, this patient had refused psychiatric consult. In general, if the patient improves with wound care and pharmaceutical management of the delusion, the physician can recommend psychiatric consultation once the delusions have been reduced. Ideally, both a psychiatrist and attending clinician would evaluate the patient in the same visit. However, this may prove challenging due to the trust issues of these patients.

   This patient moved on to another physician and I suspect a multiple number of physicians after that. Management of these patients is challenging and can be frustrating. Even though the clinician may have the best interest of the patient in mind, the patient’s delusion is so fixed and unwavering that it is a true barrier to her current care and quality of life.

   Dr. Vlahovic is an Associate Professor and J. Stanley and Pearl Landau Faculty Fellow at the Temple University School of Podiatric Medicine. She is board certified by the American Board of Podiatric Surgery.


1. Sandoz A, LoPiccolo M, Kusnir D and Tausk FA. A clinical paradigm of delusions of parasitosis. J Am Acad Dermatol. 2008; 59(4):698-704.
2. Edlich RF, Cross CL, Wack CA and Long WB. Delusions of parasitosis. Am J Emerg Med. 2009; 27(8):997-999.
3. Shmidt E and Levitt J. Dermatologic infestations. Int J Dermatol. 2012; 51(2):131-41.

   Dr. Vlahovic writes a DPM Blog for Podiatry Today at .


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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