How do you diagnose mites on the skin?

Diagnosing Skin Mites: Testing Methods and Approach

The most effective method for diagnosing skin mites is direct microscopic examination of skin samples collected through skin scraping, adhesive tape testing, or skin biopsy, depending on the suspected mite species.

Common Skin Mites and Their Diagnostic Approaches

1. Scabies (Sarcoptes scabiei)

• Primary Testing Method: Skin scraping from burrows or papules

  • Scrape the skin with a blunt scalpel, particularly from burrows, papules, or vesicles
  • Place scrapings on a glass slide with mineral oil or potassium hydroxide (10-30%)
  • Examine under microscope for mites, eggs, or fecal pellets 1, 2

• Alternative Methods:

  • Adhesive tape method: Apply strong transparent adhesive tape firmly to affected skin areas (particularly effective for severe infestations in bedridden elderly patients), then transfer to a slide for microscopy 2
  • Dermoscopy: Can visualize the characteristic "delta sign" or "jet with contrail" appearance of mites at the end of burrows (sensitivity: 43.47%, specificity: 84.41%) 3

2. Demodex Mites (Demodex folliculorum, Demodex brevis)

• Primary Testing Method: Microscopic evaluation of epilated eyelashes

  • Place epilated eyelashes on a glass slide
  • Add a drop of fluorescein and place a cover slip
  • Examine under microscope or even using a slit lamp with a 90 Diopter condensing lens 1

• Alternative Method:

  • Skin surface biopsy: Apply cyanoacrylate glue to a glass slide, press against skin, remove, and examine under microscope

Testing Approach Based on Suspected Mite Type

For Suspected Scabies:

1. Target sampling areas:

   • Finger webs
   • Wrists
   • Axillae
   • Belt line
   • Genitalia
   • Feet (especially in bedridden patients) 2

2. Collection technique:

   • Apply mineral oil to the suspected area
   • Scrape the skin with a #15 blade or curette
   • Transfer material to a slide with a drop of mineral oil
   • Apply coverslip and examine under low power microscopy 3

For Suspected Demodex:

1. Target sampling areas:

   • Eyelash follicles (for ocular manifestations)
   • Nasolabial folds
   • Forehead
   • Chin

2. Collection technique:

   • Gently epilate affected eyelashes
   • Place on slide with fluorescein
   • Examine for cigar-shaped mites 1

Diagnostic Challenges and Pitfalls

• False negatives are common: Sensitivity of skin scraping is low, especially with low mite burden
• Proper site selection is crucial: Selecting the wrong site for sampling can miss the infestation
• Laboratory expertise matters: Proper identification requires experience in recognizing mites
• Consider multiple sampling methods: Using both skin scraping and adhesive tape increases diagnostic yield 3

Special Considerations

• For severe infestations: Adhesive tape method may be more effective and less invasive, particularly in elderly or bedridden patients 2
• For suspected Demodex blepharitis: Look for lash collarettes as a clinical sign suggesting infestation 1
• For suspected tinea capitis: Wood's lamp examination may help identify affected hairs for sampling (particularly for M. canis infections) 1

When to Consider Empiric Treatment

If clinical suspicion is high despite negative diagnostic tests, consider empiric treatment, especially for:

• Patients with characteristic burrows
• Nocturnal pruritus
• Similar symptoms in household contacts
• Immunocompromised patients where mite burden may be high 4

Remember that prompt diagnosis and treatment are essential not only for patient comfort but also to prevent transmission and secondary bacterial infections that can lead to serious complications 5.