Skin nontumor

Infestations

Demodex



Last author update: 23 May 2022
Last staff update: 24 June 2022 (update in progress)

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PubMed Search: Demodex mites [title]

Bethany R. Rohr, M.D.
Eric W. Hossler, M.D.
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Cite this page: Rohr BR, Hossler EW. Demodex. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumordemodex.html. Accessed December 7th, 2022.
Definition / general
  • Demodex mites are commensal organisms that are occasionally implicated in inflammatory skin disease
Essential features
  • Commensal mite found in folliculosebaceous units
  • Increased incidence with age
  • Pathogenic with overgrowth or immune reaction causing rosacea or folliculitis
Terminology
  • Demodex mites, demodicosis, demodicidosis, Demodex folliculorum, Demodex brevis, face mite, follicle mite
ICD coding
  • ICD-10:
    • B88.0 - other acariasis (inclusion term dermatitis due to Demodex species)
    • L71.8 - other rosacea
    • L71.9 - rosacea, unspecified
    • L73.8 - other specified follicular disorder
    • L73.9 - follicular disorder, unspecified
Epidemiology
Sites
Pathophysiology
  • Unclear
  • 4 proposed mechanisms for how Demodex cause disease (J Am Acad Dermatol 2009;60:453):
    • Blockage of hair follicle and sebaceous ducts
    • Humoral or cell mediated immune reaction to mite components
    • Foreign body granulomatous reaction to mite’s exoskeleton
    • Vector role for bacteria
  • Wolbachia within Demodex may incite inflammation (Cutis 2005;76:294)
  • Upregulation of TNF alpha and IL1β in papulopustular rosacea (Clin Dermatol 2014;32:739)
  • Papulopustular reaction associated with HLA type (Cutis 2005;76:294, Clin Dermatol 2014;32:739)
    • Lack of HLA-A2 phenotype
    • HLA-Cw2 phenotype
Etiology
  • Unclear why it is pathogenic in some (Am J Dermatopathol 1996;18:589)
    • Demodex mites in 42% of 388 follicles with inflammation
    • Demodex mites in 10% of noninflamed follicles
    • 83% of follicles with Demodex with inflammation
Clinical features
Diagnosis
Case reports
Treatment
Clinical images

Images hosted on other servers:

Rosacea due to demodicosis

Granulomatous rosacea associated with Demodex

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Bethany R. Rohr, M.D., Eric W. Hossler, M.D. and Bobbi Pritt, M.D.

Inflamed follicle

Infundibulum

Nevus

Demodex mite found in rosacea papule


Demodex scraping

MIB stain

Dual MART - MIB stain

Positive stains
  • None required
  • Incidental finding of MIB positivity noted by author Eric W. Hossler, M.D. (see figure 7)
Videos

These face mites really grow on you

Demodex mite

Sample pathology report
  • Skin, face:
    • Suppurative folliculitis with Demodex (see comment)
    • Comment: In the correct clinical setting, these findings are consistent with Demodex folliculitis. Similar findings can be seen in rosacea or other acneiform process.
Differential diagnosis
  • Acne:
    • Usually teens
    • Comedones
    • Pustules, cysts, nodules
  • Bacterial folliculitis:
    • Swab or tissue culture
  • Fungal folliculitis:
    • Often in setting of tinea corporis
    • Fungal hyphae and spores within involved hair follicle
    • Tissue culture
  • Pityrosporum folliculitis (Cutis 2021;107:E40):
    • Caused by Malassezia furfur
    • Pruritic monomorphic folliculocentric pustules
    • KOH shows short hyphae and spores
    • Biopsy shows hyphae and spores in inflamed follicular infundibula
  • Eosinophilic folliculitis (Cutis 2021;107:E40):
    • Pruritic facial papules and pustules
    • 3 variants: Ofuji disease, immunosuppression associated and infancy associated
    • Peripheral eosinophilia
    • Histopathology shows follicular spongiosis with exocytosis of eosinophils
  • Miliaria (Cutis 2021;107:E40):
    • Due to occlusion of eccrine glands
    • 2 - 4 mm erythematous vesicular papules or pustules in area of occlusion
    • Not folliculocentric
Board review style question #1

Demodex mites are commensal arachnids that most commonly live in which anatomic location(s)?

  1. Arms
  2. Buttocks
  3. Face
  4. Feet and Hands
  5. Legs
Board review style answer #1
C. Face

Comment Here

Reference: Demodex
Board review style question #2
Demodex mites have been implicated in which of the following conditions?

  1. Atopic dermatitis
  2. Psoriasis
  3. Rosacea
  4. Seborrheic dermatitis
  5. Vitiligo
Board review style answer #2
C. Rosacea

Comment Here

Reference: Demodex
Board review style question #3

On histology, Demodex mites are usually identified in what?

  1. Dermis
  2. Eccrine coil
  3. Epidermis
  4. Folliculosebaceous unit
  5. Pilar muscle
Board review style answer #3
D. Folliculosebaceous unit

Comment Here

Reference: Demodex
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