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TINEA UNGUIUM
Onychomycosis is a fungal infection of the nail bed, nail plate or both. It is caused by dermatophytes, non-dermatophyte molds and yeast.
Tinea unguium or dermatophytic onychomycosis is a dermatophyte infection of the nail more commonly affecting the toenails than the fingernails.
It is usually asymptomatic and patients first consult for cosmetic reasons.
It is suspected if there are changes in the 3rd or 5th toenail, involvement of the 1st and 5th toenails on the same foot and unilateral nail changes.

Classification

  • Onychomycosis is classified based on route of infection & clinical presentation

Distal & Lateral Subungual Onychomycosis (DLSO)

  • Most common type, 90% of infections
  • Invasion occurs at distal subungual space & at the distal lateral groove
    • More commonly involves the toenails
  • Nail plate looks opacified & hyperkeratotic, its distal portion may break away
  • Splinter hemorrhages are seen secondary to mild inflammation compressing small blood vessels
  • Most common cause: Trichophyton rubrum
    • May also be caused by: Trichophyton tonsurans, Trichophyton mentagrophytes & Epidermophyton floccosum

Superficial White Onychomycosis (SWO)

  • Second most prevalent type, 10% of infections
  • Dorsal surface of the nail plate is invaded
  • Minimal inflammation; nail becomes soft & crumbly w/ a white-colored rough surface
    • Nail plate is not thickened & remains attached to the nail bed
  • Typically caused by T mentagrophytes but may also be caused by non-dermatophyte molds

Proximal Subungual Onychomycosis

  • Least common form in healthy individuals & may be an early indicator of human immunodeficiency virus (HIV) infection
  • Toenails are more commonly infected than fingernails
  • Infection enters at the cuticle & the proximal nail bed is always involved
    • Spreads distally so if left untreated, the entire nail plate will be affected
  • Nail plate is typically white in color
    • Subungual hyperkeratosis & proximal onychomycosis are usually present
  • Usually caused by T rubrum but can be caused by Trichophyton megnini, T tonsurans & T mentagrophytes

Candidal Onychomycosis

  • Commonly found in patients diagnosed w/ chronic mucocutaneous candidiasis
    • More commonly affects the fingernails
  • Candida invades the nail bed or plate directly or may indirectly involve the nail through infecting the nail bed, folds or hyponychium
  • Entire nail thickens & turns yellow-brown; progression may lead to total dystrophy of the nails
  • Usually caused by Candida albicans or other Candida sp
    • May have some resistance to oral antifungal agents

Total Dystrophic Onychomycosis

  • Most advanced form
  • Nail plate is almost completely destroyed
  • May be the end result of the above four forms

Laboratory Tests

Onychomycosis typically requires prolonged high-cost therapy; thus, the diagnosis should be confirmed before treatment is started

Microscopy

  • Specimen is mounted in 10-15% Potassium hydroxide (KOH) soln w/ calcofluor & heated gently, viewed under light microscope, & examined for hyphae & arthrospores
    • Scrapings of nail bed for distal subungual onychomyosis & scrapings from the nail plate white spots for superficial white onychomycosis
    • Calcofluor may decrease risk of false negative results
  • Presence of fungal infection can be detected but the causative organism is not specified

Culture

  • Adequate sample is inoculated onto Saboraud’s glucose agar w/ or w/o addition of antibiotics
  • Identifies organism & the specific etiologic agent so that treatment can be individualized
  • Considered the mainstay of onychomycosis diagnosis

Histology

  • Periodic acid-Schiff (PAS) staining w/ histologic exam of the clipped, distal, free edge of the nail & attached subungual debris
    • Most sensitive diagnostic method
  • PAS staining of nail plate biopsy or removed nail w/ culture is required to diagnose proximal subungual onychomycosis
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