Differential Diagnosis for Ingrown Toenail
When evaluating a suspected ingrown toenail, you must systematically exclude infectious causes (bacterial paronychia, onychomycosis, candidiasis), inflammatory conditions (psoriasis, lichen planus), structural abnormalities (subungual exostosis, tumors), and traumatic etiologies before confirming onychocryptosis.
Primary Infectious Differentials
Bacterial Paronychia
- Key distinguishing features: Acute onset with erythema, warmth, and purulent discharge from the nail fold
- Pseudomonas aeruginosa specifically causes green or black nail discoloration 1
- Can coexist with true ingrown toenail, requiring concurrent treatment 1
Candidal Paronychia
- Begins in the proximal nail fold (not lateral margins like ingrown toenails) 1
- Creates a prominent gap between fold and nail plate
- Painful with pressure and movement (unlike dermatophyte infections) 1
- More common in fingernails and patients with wet occupations 1
- Look for white, green, or black marks in proximal/lateral portions 1
Onychomycosis (Fungal Nail Infection)
- Nail surface becomes soft and friable (key differentiator from non-infectious causes) 1
- Distal and lateral subungual pattern most common, with thickening and discoloration 1
- Typically affects toenails more than fingernails 1
- Requires laboratory confirmation via microscopy/culture 1
Non-Infectious Structural Differentials
Subungual Exostosis
- Critical to exclude as it mimics ingrown toenail clinically 2
- Requires radiographic evaluation for definitive diagnosis
- Presents as painful mass under nail plate
Subungual Tumors
- Including subungual malignant melanoma 1
- Look for pigmentation changes, single nail involvement
- Warrants biopsy if clinical suspicion exists
Chronic Trauma
- Repetitive trauma causes distal onycholysis with secondary colonization 1
- Diagnostic clue: Nail bed examination shows normal appearance with intact longitudinal epidermal ridges stretching to lunula 1
- Differs from onychomycosis where nail bed is abnormal
Inflammatory/Dermatologic Differentials
Psoriasis
- Nail pitting, onycholysis, subungual hyperkeratosis
- Usually multiple nails affected
- Look for associated skin lesions 1
Lichen Planus
- Affects ~10% of lichen planus patients
- Thinning of nail plate, subungual hyperkeratosis, dorsal pterygium 1
- Associated with characteristic skin findings
Yellow Nail Syndrome
- Frequently misidentified as fungal infection 1
- Light green-yellowish pigmentation, hardness, elevated longitudinal curvature 1
Special Considerations
Retronychia and Onychomadesis
- One nail growing below another 3
- Can present as chronic paronychia mimicking ingrown toenail
- Requires detailed history of trauma or tape application 3
Hallux Valgus Association
- Abnormal hallux valgus angle significantly associated with lateral border ingrown toenails 4
- Consider foot X-rays in recurrent cases to identify structural predisposition 4
Clinical Pitfalls to Avoid
Don't assume all lateral nail fold inflammation is simple onychocryptosis - bacterial superinfection is common and may require separate antimicrobial therapy 1
Single nail involvement with treatment failure should prompt consideration of nondermatophyte mould infection or tumor 1
Proximal nail involvement strongly suggests Candida or proximal subungual onychomycosis (PSO), not typical ingrown toenail 1
Green/black discoloration = Pseudomonas until proven otherwise 1
In pediatric patients, consider anatomical foot structure and gait abnormalities that may contribute to recurrence 5