Formication, a sensation that resembles that of insects crawling on or under the skin, is a specific form of the general set of abnormal skin sensations known as paresthesias (prickling, tingling sensation of "pins and needles") and tactile hallucinations; it is a well-documented symptom that has numerous possible causes.
Recent attention to the presumed role of Demodex in skin and ocular disease has generated novel information that is readily available via an Internet search. Certainly, we at Optometry Times have propagated a good deal of Demodex information. I am confident that every day you encounter a patient who has self-diagnosed an ocular condition by entering a few key words into the Google search box. The top Google hit for “blepharitis itchy eyelids” is from the respected Mayo Clinic that includes Demodex in the differential diagnosis.1 Therefore, it is no surprise that patients who carry the diagnosis of blepharitis will question if the Demodex mite is contributing to their malady.
Formication, a sensation that resembles that of insects crawling on or under the skin, is a specific form of the general set of abnormal skin sensations known as paresthesias (prickling, tingling sensation of "pins and needles") and tactile hallucinations; it is a well-documented symptom that has numerous possible causes.2
Associated conditions and drugs
Formication can be a physical or psychological side effect of:
• Substance abuse
• Diabetic neuropathy
• Diseases of the spinal cord and peripheral nerves
• Multiple sclerosis
• Extreme alcohol withdrawal.
It is associated with:
• Autoimmune disease
• Hepatic disease
• Thyroid disease
Drugs that have been reported to cause formication include:
• Adderall (mixed salts of a single-entity amphetamine, Shire)
• Crystal meth
• Keppra (levetiracetam, UCB)
• Lunesta (eszopiclone, Sunovion)
• Ritalin (methylphenidate, Novartis)
• Wellbutrin (bupropion, Valeant)
Interestingly, a small percentage of menopausal women report itchy skin symptoms or formication. In fact, skin paresthesias are included in the Kuppeman/Modified Kupperman Menopausal Index.3 The Kupperman Index, along with the more recently devised Menopausal Rating Scale,4 are tools for the assessment of menopausal complaints.
It should be noted that susceptible individuals who fixate on the sensation of formication may develop delusional parasitosis, also known as Ekbom or Morgellon’s syndrome. Classified as a primary psychiatric disorder, the patient has no primary skin pathology; all skin findings are secondary to skin manipulation by the patient, e.g., excessive scratching. The prototypical patient with delusory parasitosis is an older woman. Patients with this disorder may be fully functional, but have a false belief that they are infested with parasites despite repeated reassurances from physicians, pest control experts, and entomologists that they are not.
These patients profess to have the parasites in a collection of material (typically pieces of skin, scabs, hair, lint, dried blood, living organisms such as flies or ants, and other debris) and request that it be studied under a microscope or sent to a laboratory for identification. This clinical presentation is called the "matchbox sign" because patients have often used a matchbox to collect the material.5
Through my personal communications, recent clinical experience from practices across the country have raised my awareness of delusional parasitosis. I admonish practitioners to thoroughly process a patient’s complaints and medical history before assigning disease culpability to the ubiquitous mite. To wit, careful monitoring of a patient’s emotional demeanor is paramount when managing diagnosed parasitic disease.ODT
1. Mayo Clinic website. Diseases and Conditions: Blepharitis. Available at http://www.mayoclinic.org/diseases-conditions/blepharitis/basics/definition/con-20024605. Accessed 04/14/2014.
2. Hinkle NC. Delusory parasitosis. American Entomologist. Spring 2000;46(1)1:17-25.
3. Kupperman HS, Blatt MH, Wiesbader H, et al. Comparative clinical evaluation of estrogenic preparations by the menopausal and amenorrheal indices. J Clin Endocrinol Metab. 1953 Jun;13(6):688–703.
4. Hauser GA, Huber IC, Keller PJ, et al. Evaluation of climacteric symptoms (Menopause Rating Scale). Zentralbl Gynakol. 1994;116(1):16–23.
5. Freudenmann RW, Lepping P. Delusional Infestation. Clin Microbiol Rev. 2009 Oct;22(4):690-732