What are the causes and treatment options for nail deformities in patients with potential underlying systemic conditions such as fungal infections, psoriasis, or trauma?

Nail Deformities: Causes and Treatment

Nail deformities require mycological confirmation before treatment when fungal infection is suspected, as approximately 50% of dystrophic nails are non-fungal despite similar clinical appearance, and definitive diagnosis fundamentally changes management. 1

Diagnostic Approach

Initial Clinical Assessment

Examine the nail texture and characteristics to narrow the differential:

• Soft, friable texture suggests fungal infection (onychomycosis), which presents with thickening, yellow-brown discoloration, and onycholysis 2, 1
• Hard, brittle texture with longitudinal ridging indicates non-infectious causes such as aging, inflammatory conditions (psoriasis, lichen planus), or systemic disease 3
• Paronychia (nail fold swelling/erythema) with proximal nail involvement suggests Candida infection, particularly in patients with occupational moisture exposure 3
• Green or black discoloration indicates bacterial infection, typically Pseudomonas aeruginosa 2

Critical Pitfall to Avoid

Never assume fungal infection based on clinical appearance alone—the nail surface in fungal infections becomes soft and friable, unlike the hard texture of non-infectious dystrophies, but visual inspection cannot definitively distinguish between conditions 4. Laboratory confirmation is essential before initiating antifungal therapy 1, 5.

Laboratory Confirmation for Suspected Fungal Infection

When fungal infection is suspected, obtain:

• Potassium hydroxide (KOH) preparation with direct microscopy 1
• Fungal culture on Sabouraud's glucose agar 3, 1
• Calcofluor white staining to enhance visualization of fungal elements and increase sensitivity 4, 1

Collect specimens from discolored, dystrophic, or brittle parts of the nail, cutting through the entire thickness and including crumbly material 2.

Common Causes by Category

Infectious Causes

Fungal infections (onychomycosis):

• Account for 15-40% of all nail diseases in adults 3
• Trichophyton rubrum causes approximately 64% of cases 1
• Distal and lateral subungual onychomycosis (DLSO) is the most common pattern, with toenails affected more than fingernails 1
• Nondermatophyte moulds account for approximately 5% of UK cases and 20% of North American cases 2

Candida infections:

• Begin in the proximal nail plate with associated paronychia 2
• Strongly associated with chronic moisture exposure and wet occupations 3

Bacterial infections:

• Pseudomonas aeruginosa produces green discoloration (Green Nail Syndrome) 3
• May coexist with fungal infection 2

Inflammatory Dermatologic Conditions

Psoriasis:

• Nail involvement occurs in 10-80% of psoriasis patients 6
• Presents with pitting, onycholysis, subungual hyperkeratosis, and oil drop discoloration 6
• Dystrophic nails in psoriasis are more predisposed to secondary fungal infections (62% prevalence in one study) 6

Lichen planus:

• Affects approximately 10% of patients with lichen planus 4
• Produces thinning of the nail plate with subungual hyperkeratosis, longitudinal ridging, onycholysis, and dorsal pterygium 3, 4

Medication-Related Causes

Chemotherapeutic agents:

• Taxanes (docetaxel, paclitaxel) cause dose-dependent onychorrhexis, ridging, thinning, and nail fragility 3
• Other agents including capecitabine, etoposide, cytarabine, cyclophosphamide, and doxorubicin cause mild to moderate nail changes 3
• Targeted therapies (mTOR inhibitors, EGFR inhibitors, MEK inhibitors) also cause nail alterations 3

Other medications:

• Tetracyclines and quinolones cause photosensitivity-related nail plate detachment and discoloration 7
• Retinoids and psoralens produce similar effects 7

Systemic and Nutritional Causes

Screen for underlying conditions when brittle nails are present:

• Biotin deficiency (daily supplementation shows 63% clinical improvement) 3
• Iron deficiency anemia 3
• Thyroid dysfunction 3

Check thyroid function and complete blood count as part of the diagnostic workup 3.

Trauma and Aging

• Vertical ridges from cuticle to nail tip are often normal aging as the nail matrix's ability to produce smooth nails diminishes 3
• Chronic trauma from occupational exposure or repetitive injury produces dystrophic changes 2

Treatment Algorithm

For Confirmed Fungal Infections

Systemic antifungal therapy (only after mycological confirmation):

• Terbinafine or itraconazole are first-line agents 3
• Daily urea-based keratolytic cream to reduce nail thickness if needed 3

For Inflammatory Conditions (Psoriasis, Lichen Planus)

When affecting fewer than 3 nails:

• Intralesional triamcinolone acetonide 5-10 mg/cc for nail matrix involvement 3
• Topical steroids with or without vitamin D analogs for nail bed involvement 3

For Medication-Induced Horizontal Ridges

• Daily dilute vinegar soaks to nail folds twice daily for 10-15 minutes 3
• Mid to high potency topical steroid ointment to nail folds twice daily 3
• Consider temporary dose adjustment of causative medication in consultation with prescribing physician 3

For Bacterial Infections (Green Nail Syndrome)

• Keep affected area dry 3
• Apply topical povidone iodine 2% twice daily 3

For Chronic Paronychia (Candida)

Treatment targets the underlying moisture exposure and inflammation 3.

General Preventive Measures for All Nail Deformities

• Apply daily topical emollients to periungual folds, nail matrix, and nail plate 3
• Use protective nail lacquers to limit water loss 3
• File nail surfaces gently with an emery board after softening in warm water 3
• Avoid trauma, nail biting, use of nails as tools, prolonged water soaking, and harsh chemical exposure 3
• Wear gloves while cleaning or working with chemicals, especially for patients with chronic moisture exposure 3

For Brittle Nails Without Infection

• Daily topical emollients on periungual folds and protective nail lacquers 3
• Biotin supplementation if deficiency suspected 3
• Address underlying systemic conditions (thyroid, anemia) 3

Key Clinical Pearls

• Suspect nondermatophyte mould when previous antifungal treatment has failed repeatedly, direct microscopy is positive but no dermatophyte isolated, and no associated skin infection is present 2
• Candida nail infections typically begin proximally with paronychia, unlike dermatophyte infections which start distally 2
• Patients with psoriasis and nail deformities require mycological examination due to high prevalence (62%) of concurrent onychomycosis 6
• Occupational counseling is essential for patients with chronic moisture exposure to prevent recurrence 3