Describing onychomycosis on physical exam means documenting the nail’s color change, the pattern of involvement, the degree of thickening or separation, and which subtype the findings match. A thorough description includes which nails are affected, the percentage of nail area involved, how close the disease extends toward the nail matrix, and whether subungual debris or hyperkeratosis is present. These details guide both the clinical subtype classification and severity scoring that determine treatment decisions.
Key Descriptors to Document
A complete exam note for a suspected fungal nail should address five core features: color, nail plate integrity, onycholysis, subungual changes, and nail surface texture. For color, onychomycosis typically produces yellow to brown discoloration, distinguishing it from the salmon or oil-drop spots seen in nail psoriasis. The discoloration often starts at the distal or lateral edge and progresses proximally.
Onycholysis refers to separation of the nail plate from the underlying nail bed, usually starting distally. Document how far proximally the separation extends, as this directly affects severity scoring. Beneath the detached plate, you’ll often find subungual hyperkeratosis: a buildup of white, chalky keratin debris between the nail plate and the bed. Note its thickness, as hyperkeratosis greater than 2 mm is considered a marker of severe disease. The nail plate itself may appear thickened, crumbling, or friable. In advanced cases, ridging of the nail bed becomes visible once the damaged plate is debrided or lost.
Clinical Subtypes and How They Present
Classifying the subtype in your documentation helps narrow the causative organism and informs management. There are four recognized presentations.
Distal lateral subungual onychomycosis (DLSO) is by far the most common. It presents with partial onycholysis starting at the distal or lateral nail edge, accompanied by subungual hyperkeratosis or crumbling of the distal plate. You might document it as: “Yellow-brown discoloration of the distal one-third of the right great toenail with onycholysis and subungual hyperkeratotic debris.” The infection advances proximally over time, so noting the boundary between diseased and healthy nail is important.
White superficial onychomycosis (WSO) looks distinctly different. The nail surface develops opaque, milky-white patches or a diffuse chalky appearance. The discoloration is superficial, confined to the dorsal plate rather than the nail bed. In more extensive cases, the entire nail plate becomes opaque white and friable. A useful descriptor: “Diffuse opaque white discoloration of the nail plate surface with a powdery, friable texture.”
Proximal subungual onychomycosis (PSO) is the rarest subtype and begins near the proximal nail fold, with whitish discoloration developing in the area overlying the nail matrix and extending distally. This pattern is a clinical marker for immunosuppression, so documenting it accurately can prompt further workup. Describe it as involving the proximal plate first, with the distal nail initially appearing normal.
Total dystrophic onychomycosis (TDO) represents the end stage of any chronic subtype, typically developing over 10 to 15 years. The entire nail plate is destroyed or severely dystrophic, with significant subungual hyperkeratosis and nail bed ridging. Documentation here often notes complete nail plate destruction, thick debris, and loss of normal nail architecture.
Grading Severity With the Onychomycosis Severity Index
The Onychomycosis Severity Index (OSI) provides a standardized way to translate your physical exam findings into a numerical score. It multiplies two factors: the percentage of nail area involved (scored 1 through 5) and the proximity of disease to the matrix (scored 1 through 5, with 5 indicating matrix involvement). This product gives a baseline score. If a dermatophytoma (a dense, yellowish-white or brown streak within the nail) or subungual hyperkeratosis greater than 2 mm is present, 10 points are added.
For example, a nail with roughly 20% area involvement affecting only the distal edge scores low, perhaps 2 multiplied by 2 for a total of 4 (mild). A nail with matrix involvement and a lateral streak could score 15 or higher, indicating severe disease that may not respond to topical therapy alone. Including this score or its component observations in your note gives other clinicians a reproducible measure of disease burden.
Distinguishing Onychomycosis From Nail Psoriasis
The most common look-alike on physical exam is nail psoriasis, and the two can coexist. Several features help differentiate them. Nail pitting, the small uniform depressions scattered across the nail surface, is very common in psoriasis and rare in onychomycosis. When pitting does occur with fungal infection, the pits tend to be irregular in size and shape, unlike the evenly spaced, uniform pits of psoriasis.
Oil-drop spots (also called salmon patches) are a hallmark of nail psoriasis: yellowish-brown translucent areas that look like a drop of oil soaking through paper, often with a reddish proximal margin. These are not a feature of onychomycosis. Psoriatic onycholysis also has a distinctive reddish border at its proximal edge, while fungal onycholysis does not. Documenting the absence of pitting and oil-drop spots in your exam note strengthens the case for a fungal etiology.
Dermoscopy Findings Worth Noting
If you use a dermatoscope during your exam, several patterns are highly specific for onychomycosis. The “ruin appearance,” describing an irregular, crumbled look to the nail plate, has a specificity above 99%. Longitudinal striae, which are streaks of varying pigmentation running along the length of the nail plate, result from fungal invasion and appear in roughly 65% of cases. At the proximal edge of the onycholytic area, look for a jagged border with sharp, spike-like white indentations pointing toward the proximal fold. These spikes correspond to the fungus advancing along the nail bed’s longitudinal ridges.
The “aurora borealis” sign combines several of these features: multicolored areas of green, bluish-gray, black, white, and yellow interspersed with longitudinal striae, spikes, and onycholysis. It resembles waves of northern lights and, in studies, showed 85% sensitivity and 100% specificity for onychomycosis. Noting these dermoscopic findings adds diagnostic weight to your clinical description.
Associated Findings to Include
Onychomycosis rarely exists in isolation. During your exam, check for concurrent tinea pedis, which shares the same causative organisms. The interdigital form presents as erythema, maceration, fissuring, and scaling between the fourth and fifth toes. The moccasin type shows chronic plantar erythema with diffuse, fine scaling in a slipper-like distribution. Documenting these findings supports the diagnosis and suggests the source of reinfection if treatment fails. Tinea of the groin and hands may also be present.
Why Visual Diagnosis Alone Falls Short
A well-documented clinical exam is essential but insufficient on its own. In a study of diagnostic accuracy in general practice, clinical examination had 100% sensitivity, meaning clinicians correctly identified essentially every true case. However, specificity was 0%, meaning a large proportion of nails that looked fungal on exam turned out to be something else on confirmatory testing. The positive predictive value of a clinical diagnosis ranged from about 27% to 75% depending on the confirmatory method used. This means your physical exam description should explicitly state that the findings are “consistent with” or “suggestive of” onychomycosis, with laboratory confirmation recommended before starting systemic treatment. Nail clippings for fungal culture, microscopy with potassium hydroxide preparation, or molecular testing close the diagnostic gap that the physical exam alone cannot.