Treating A Patient Who Feels There Are Parasites Under Her Skin
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.”