What is the likely cause of nail discoloration at the proximal edge after removing nail polish in a non-diabetic patient with no known vascular disease?

Proximal Nail Discoloration After Nail Polish Removal

The most likely cause is cosmetic staining from nail polish or nail polish remover, but you must rule out proximal subungual onychomycosis (PSO), which presents with white discoloration at the proximal nail edge and can be an early marker of immunosuppression. 1

Primary Diagnostic Considerations

Cosmetic-Related Causes (Most Common)

• Nail polish staining is the most frequent benign cause of proximal nail discoloration in patients with repeated manicure exposure, particularly with darker pigmented polishes 2
• Pseudoleukonychia occurs when white discoloration affects only the nail surface and can be scraped off, distinguishing it from true nail plate pathology 2
• The timing (appearing after polish removal) and recurrent pattern with manicures strongly suggests a cosmetic etiology rather than systemic disease 2

Infectious Causes Requiring Exclusion

Proximal Subungual Onychomycosis (PSO):

• PSO originates in the proximal nail fold and penetrates the newly forming nail plate, causing white discoloration at the proximal margin that progresses distally 1
• T. rubrum is the usual causative organism 1
• Critical red flag: PSO is uncommon in the general population but is common in persons with AIDS and has been considered a useful marker of HIV infection 1
• In immunocompromised patients, PSO spreads rapidly from the proximal margin to produce gross white discoloration without obvious thickening 1

Candidal Onychomycosis:

• Chronic paronychia with secondary nail dystrophy occurs in patients with wet occupations or chronic water immersion 1
• Infection and inflammation in the nail matrix area lead to proximal nail dystrophy 1
• White, green, or black marks appear in the proximal and lateral portions of the nail 1

Diagnostic Algorithm

Step 1: Clinical Assessment

• Examine the discoloration pattern: Surface-only involvement that can be gently scraped suggests pseudoleukonychia from cosmetic products 2
• Check for paronychia: Swelling, erythema, or tenderness of the proximal nail fold suggests candidal infection 1, 3
• Assess nail plate integrity: True PSO involves the nail plate itself with progression toward the distal nail, while cosmetic staining remains superficial 1, 2

Step 2: Risk Factor Evaluation

• Occupational exposure: Wet occupations (housekeepers, dishwashers, bartenders) increase risk for candidal paronychia 3
• Immunosuppression screening: Given that PSO can be a marker of HIV infection, consider risk factors for immunocompromise 1
• Medication history: Complete drug history to exclude chemotherapy-induced melanonychia, though this typically causes brown-to-black discoloration rather than white 4

Step 3: Confirmatory Testing (If Infection Suspected)

• Obtain nail specimens from discolored areas for KOH preparation and fungal culture on Sabouraud's agar 4, 5
• Calcofluor white staining enhances visualization of fungal elements 4
• Nail clippings should be taken from the proximal portion where discoloration is present 5

Management Approach

If Cosmetic Staining (Most Likely)

• Reassure the patient that superficial staining is benign 2
• Recommend nail polish holiday: Allow nails to recover between manicures
• Use base coat: Apply protective base coat before colored polish to prevent future staining
• Avoid acetone-based removers: These can damage the nail surface and increase staining susceptibility

If PSO Confirmed

• Systemic antifungal therapy is required as topical agents cannot adequately penetrate to the proximal nail matrix 1, 5
• Treatment duration is typically 6-12 months given the slow nail growth rate 5
• Address underlying immunosuppression if PSO is confirmed, as this may indicate HIV or other immune dysfunction 1

If Candidal Infection Confirmed

• Treat chronic paronychia with topical povidone iodine 2% twice daily for bacterial superinfection 4
• Address predisposing factors: Minimize water exposure, use protective gloves, apply daily emollients to cuticles 3
• Consider systemic antifungals if nail plate involvement is extensive 1

Critical Pitfalls to Avoid

• Do not dismiss proximal white discoloration without proper evaluation: While cosmetic staining is most common, PSO can be a marker of serious immunosuppression 1
• Do not assume all white nail discoloration is fungal: Up to 50% of nail diseases are non-fungal, including trauma, psoriasis, and lichen planus 6
• Do not treat empirically without confirmation: Misdiagnosis leads to treatment failure and delayed recognition of underlying systemic disease 6
• Do not overlook occupational factors: Chronic water exposure predisposes to candidal paronychia, which requires lifestyle modification in addition to antifungal therapy 3