Workup for Skin and Nail Changes
The workup for skin and nail changes must begin with proper specimen collection for laboratory confirmation—specifically nail clippings and scrapings for direct microscopy and fungal culture—because clinical examination alone cannot reliably distinguish between infectious and non-infectious causes, and misdiagnosis leads to inappropriate treatment. 1
Clinical Assessment Framework
Initial Examination: Key Distinguishing Features
When evaluating nail changes, focus on these specific clinical patterns:
Location and Distribution:
- Proximal nail plate involvement with paronychia → suspect Candida infection 1
- Distal/lateral nail changes → most likely dermatophyte infection (DLSO pattern) 1
- Single nail involvement → consider nondermatophyte mould or trauma 1
- Green or black discoloration → bacterial infection (Pseudomonas aeruginosa) 1
Nail Texture:
- Soft and friable surface → fungal infection likely 1
- Hard nail with intact surface → non-infectious causes more probable 1
Associated Findings:
- Check for skin lesions on feet, hands, or groin (suggests dermatophyte spread) 1
- Examine nail bed after clipping: intact longitudinal epidermal ridges to lunula = trauma, not infection 1
Essential Laboratory Workup
Specimen Collection Technique (Critical for Accuracy)
For suspected fungal infection 1:
- Take material from discolored, dystrophic, or brittle parts
- Cut affected nail as far back as possible through entire thickness
- Include any crumbly material
- Use sterilized nail drills, scalpels, or elevators between patients
- For superficial involvement: use curette for nail scrapings
- If skin lesions present: sample these too (higher culture yield)
Laboratory Tests to Order
Standard workup 1:
- Direct microscopy with Calcofluor white (preferred over KOH—increases sensitivity by making fungal elements more visible)
- Fungal culture (results in 2-6 weeks)
Advanced diagnostics when available 1:
- Real-time PCR (turnaround <2 days, higher detection rate than culture)
- Caveat: May detect dead/non-pathogenic fungus, limiting pathogen identification
- Histopathology with PAS staining (more sensitive than microscopy or culture, but not widely available)
Differential Diagnosis Algorithm
When to Suspect Non-Infectious Causes 1
Psoriasis indicators:
- Nail pitting
- Subungual hyperkeratosis
- Onycholysis
- Associated skin psoriasis
Lichen planus (10% have nail involvement):
- Nail plate thinning
- Dorsal pterygium
- Subungual hyperkeratosis
Trauma:
- Distal onycholysis pattern
- Normal nail bed on examination
- History of repetitive injury
Subungual malignant melanoma:
- Must be excluded in appropriate clinical context
- Requires biopsy if suspected
Yellow nail syndrome:
- Light green-yellowish pigmentation
- Hardness
- Elevated longitudinal curvature
When to Suspect Specific Infections
Nondermatophyte mould 1:
- Previous antifungal treatment failures (multiple attempts)
- Positive microscopy but no dermatophyte isolated
- No associated skin infection
- Often single nail involvement
Candida 1:
- Proximal nail plate involvement
- Paronychia present
- More common in women
- Fingernails > toenails
Common Pitfalls to Avoid
Never treat empirically without laboratory confirmation 2—studies show testing is cost-effective to prevent inappropriate therapy
Don't assume all nail dystrophy is fungal—many non-infectious conditions mimic onychomycosis 1
Don't rely on single negative culture—specimen quality is crucial; repeat if clinical suspicion high 1
Don't ignore coexisting bacterial infection—may require separate treatment 1
Recognize that PCR positivity doesn't always mean active infection—can detect dead organisms 1
When to Refer
Immediate dermatology referral indicated for:
- Suspected subungual melanoma 1
- Ambiguous clinical presentation requiring biopsy 3, 4
- Chronic mucocutaneous candidiasis 1
- Failed treatment despite confirmed diagnosis 3
Dermoscopy (onychoscopy) enhances diagnostic accuracy 4, 5 and should be performed when available, particularly for:
- Subtle etiologic patterns
- Vascular changes in nail bed/hyponychium
- Proximal nail fold abnormalities