Tinea%20unguium Diagnosis
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