Skin nontumor
Infestations
Demodex
Topic Completed: 1 June 2011
Minor changes: 6 October 2020
Copyright: 2002-2021, PathologyOutlines.com, Inc.
PubMed Search: Demodex [title] skin
Table of Contents
Definition / general | Epidemiology | Sites | Clinical features | Case reports | Microscopic (histologic) description | Microscopic (histologic) images | VideosCite this page: Hamodat M. Demodex. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumordemodex.html. Accessed March 5th, 2021.
Definition / general
- Mites are commonly present in inflamed follicles but are usually nonpathogenic (Wikipedia: Demodex [Accessed 14 February 2019])
- Common in dogs
- Demodex folliculorum is also known as the follicle mite
- Typically considered harmless
Epidemiology
- Common in basal cell carcinomas removed from the eyelids
Sites
- Occurs on hair follicles, typically on face but anywhere on skin or nails (Pritt: Creepy Dreadful Wonderful Parasites Blog - Answer to Case 503 [Accessed 13 February 2019])
Clinical features
- 2 species are human parasites: D. folliculorum and D. brevis (Pritt: Creepy Dreadful Wonderful Parasites Blog - Answer to Case 535 [Accessed 23 April 2019])
- Demodex folliculorum lives in hair follicles and has a long opisthosoma (abdomen / posterior end)
- D. brevis lives in sebaceous glands attached to hair follicles and has a shorter opisthosoma
- Molecular analysis (16S rDNA) can also differentiate the 2 species
Case reports
- Elderly woman from Florida with toe nail scraping and fungal smear and culture (Pritt: Creepy Dreadful Wonderful Parasites Blog - Case of the Week 503 [Accessed 13 February 2019])
- Patient with Demodex seen in a scraping of a rosacea papule (Pritt: Creepy Dreadful Wonderful Parasites Blog - Case of the Week 535 [Accessed 23 April 2019])
Microscopic (histologic) description
- Follicular dilatation, the presence of dense homogenous eosinophilic material surrounding the mites, folliculitis and perifollicular chronic inflammation
- Often is a granulomatous reaction to extrafollicular Demodex, usually in granulomatous or pustular rosacea
- May see telangiectasia of superficial vessels, perifollicular granuloma and mild perivascular chronic inflammation
Microscopic (histologic) images
Contributed by Bobbi Pritt, M.D.
Toe nail of elderly
Florida woman -
KOH Calcofluor staining
of Demodex folliculorum
Adult Demodex
folliculorum has
8 legs, typical of
arachnids, not insects
Demodex mite found in rosacea papule
Videos
Demodex mite
