Medical Description of a Thick, Yellow Toenail
A thick, yellow toenail is medically described as onychomycosis, most commonly presenting as distal and lateral subungual onychomycosis (DLSO), characterized by nail plate thickening, yellow-brown discoloration, and varying degrees of onycholysis (separation of the nail plate from the nail bed). 1
Clinical Terminology and Features
The proper medical description includes these specific characteristics:
- Nail plate thickening (subungual hyperkeratosis) - the nail becomes abnormally thick due to fungal invasion of the nail bed 1
- Yellow to brown discoloration - the color change ranges from white to yellow to brown depending on the extent of fungal involvement 2
- Onycholysis - separation of the nail plate from the underlying nail bed, typically starting distally and progressing proximally 1
- Dystrophic nail changes - the nail edge becomes uneven with streaks of discolored, dystrophic nail extending toward the distal border 2
- Friable texture - the nail becomes brittle and crumbly in advanced cases 3
Classification Pattern
DLSO (Distal and Lateral Subungual Onychomycosis) is the most common clinical pattern, accounting for the majority of fungal nail infections in adults, where the fungus invades through the distal or lateral nail margins 1
- Toenails are more commonly affected than fingernails in this pattern 1
- The infection begins at the hyponychium or lateral nail sulcus, reaching the nail bed and moving proximally toward the matrix 2
- Trichophyton rubrum is the causative organism in the majority of cases (64% in some series) 4
Important Diagnostic Caveats
Do not diagnose onychomycosis based on appearance alone - approximately 50% of dystrophic nails are non-fungal despite similar clinical presentation 3, 4
- Alternative diagnoses include psoriasis, lichen planus, trauma, and yellow nail syndrome 4
- Mycological confirmation is essential before initiating treatment through potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar 3, 4
- Calcofluor white staining enhances visualization of fungal elements 4
Additional Descriptive Terms
When documenting, consider specifying:
- Degree of nail involvement - percentage of nail plate affected (important for treatment selection) 5
- Matrix involvement - whether the proximal nail matrix shows signs of infection (critical for treatment choice) 5
- Associated findings - presence of onycholysis, subungual debris, or nail bed inflammation 1
- Pattern distribution - which nails are affected and whether there is concurrent tinea pedis 4