What are the differential diagnoses, evaluation, and management for thick brown brittle fingernails?

Thick Brown Brittle Fingernails: Differential Diagnosis, Evaluation, and Management

Primary Recommendation

Obtain mycological confirmation with potassium hydroxide (KOH) preparation and fungal culture before initiating any treatment, as approximately 50% of dystrophic nails are non-fungal despite appearing clinically identical to onychomycosis. 1, 2

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Differential Diagnosis

Infectious Causes

Fungal infections (onychomycosis) are the most likely cause when fingernails present with thickening, brown discoloration, and brittle texture, particularly if the nail has a soft, friable quality. 1, 3

• Dermatophyte infection (most commonly Trichophyton rubrum) typically begins distally and progresses proximally, causing subungual hyperkeratosis, onycholysis, and nail plate thickening. 2, 4
• Candida infection should be suspected when paronychia (swollen, erythematous nail folds) is present, especially in patients with occupational moisture exposure or wet work. 1, 3
• Non-dermatophyte moulds account for approximately 5% of UK cases and 20% of North American cases, and should be suspected when previous antifungal treatment has repeatedly failed. 1, 3

Bacterial infection (Green Nail Syndrome from Pseudomonas aeruginosa) can cause dark discoloration but typically presents with green rather than brown coloration. 3, 5

Non-Infectious Causes

Psoriasis presents with nail pitting, oil drop sign, subungual hyperkeratosis, and typically involves multiple nails with associated cutaneous plaques. 3, 2

Lichen planus causes nail plate thinning with longitudinal ridging, subungual hyperkeratosis, and occasional pigmentation—approximately 10% of lichen planus cases involve nails. 3, 2

Trauma from repeated microtrauma or occupational injury can mimic fungal infection but examination of the nail bed shows intact longitudinal epidermal ridges. 2, 6

Brittle nail syndrome (onychorrhexis) presents with longitudinal ridging and splitting without infection, often related to aging, nutritional deficiencies, or medication side effects. 3

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Diagnostic Evaluation

Clinical Examination

Assess nail texture: Soft, friable texture strongly suggests dermatophyte infection, whereas hard, brittle texture indicates non-infectious causes. 3

Examine for paronychia: Swollen, erythematous nail folds with a gap between the proximal nail fold and nail plate point toward Candida infection rather than dermatophyte onychomycosis. 3

Document distribution: Involvement of only one or a few nails suggests fungal infection or trauma, while involvement of most or all nails suggests inflammatory conditions like psoriasis or lichen planus. 6

Check for associated findings: Look for tinea pedis (suggests dermatophyte), occupational wet work history (suggests Candida), or cutaneous psoriatic plaques. 1, 3

Laboratory Confirmation

Mandatory mycological testing before treatment: Never diagnose fungal infection based on appearance alone, as 50% of dystrophic nails are non-fungal. 2, 7

Specimen collection technique:

• Collect subungual debris from the most proximal part of the infection using a dental scraper. 3
• For distal lateral subungual onychomycosis, scrape material from beneath the nail plate and from the nail bed itself. 3
• Submit as much material as possible due to the relative paucity of fungal elements. 3

Testing methods (in order of preference):

1. KOH preparation with microscopy as first-line screening to visualize fungal elements. 3, 2
2. Calcofluor white staining significantly increases sensitivity compared to KOH alone. 3, 2
3. Fungal culture on Sabouraud's glucose agar to identify specific pathogen species, incubated at 28°C for at least 3 weeks. 3, 2
4. Histopathological examination with periodic acid-Schiff (PAS) staining is more sensitive than direct microscopy or culture in recent studies. 2

Additional screening for systemic conditions:

• Thyroid function tests and complete blood count to screen for thyroid dysfunction and iron deficiency anemia as potential aggravating factors. 3
• Consider biotin deficiency, which causes brittle nails and shows 63% clinical improvement with supplementation. 3

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Management Algorithm

For Confirmed Fungal Infection

First-line systemic therapy (preferred for fingernails):

Oral terbinafine is the preferred first-line treatment with superior efficacy over other agents. 5, 7

• Dosing: 250 mg daily for adults; weight-based for children (<20 kg: 62.5 mg/day; 20-40 kg: 125 mg/day; >40 kg: 250 mg/day). 5
• Duration: 6 weeks for fingernails. 5
• Monitoring: Baseline liver function tests and complete blood count; monitor for drug-drug interactions with tricyclic antidepressants, SSRIs, atypical antipsychotics, beta blockers, or tamoxifen. 5, 7

Alternative systemic therapy:

Itraconazole pulse therapy is equally effective as first-line treatment, particularly useful when Candida species are suspected. 5, 8

• Dosing: 200 mg twice daily for 1 week per month (adults); 5 mg/kg/day for 1 week per month (children). 5
• Duration: 2 pulses (2 months total) for fingernails. 5
• Monitoring: Liver function tests, particularly for patients with pre-existing abnormalities or receiving continuous therapy >1 month. 5

Topical therapy (for mild to moderate disease or when systemic therapy contraindicated):

Ciclopirox 8% nail lacquer as a component of comprehensive management with monthly professional nail debridement. 9

• Application: Apply evenly over entire nail plate and 5 mm of surrounding skin daily. 9
• Duration: Up to 48 weeks with monthly professional removal of unattached, infected nail. 9
• Efficacy: Complete cure rates of 5.5-8.5% in clinical trials; less effective than oral agents but fewer adverse effects. 9, 7

Alternative topical agents: Efinaconazole 10% or tavaborole 5% have similar efficacy profiles to ciclopirox with fewer adverse effects and drug-drug interactions. 7

Adjunctive Measures (Essential for All Patients)

Nail debridement: Professional removal of unattached, infected nail as frequently as monthly improves treatment response. 9, 7

Daily nail care:

• Apply topical emollients to periungual folds, nail matrix, and nail plate to maintain hydration. 3
• Use protective nail lacquers to limit water loss from the nail plate. 3
• File nail surfaces gently with an emery board after softening in warm water. 3

Preventive measures:

• Keep affected area dry and avoid prolonged water exposure. 3, 5
• Wear protective gloves during wet work or when handling chemicals. 3
• Apply regular antifungal powder inside shoes and periodic terbinafine solution spraying into shoes. 5
• Avoid walking barefoot in public places to prevent recurrence (25% relapse rate). 7

For Non-Fungal Causes

Psoriasis or lichen planus (affecting <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

Brittle nail syndrome:

• Daily topical emollients to cuticles and periungual tissues. 3
• Biotin supplementation for confirmed deficiency. 3
• Avoid trauma, nail biting, prolonged water soaking, and harsh chemical exposure. 3

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Critical Pitfalls to Avoid

Never initiate antifungal treatment without mycological confirmation—treatment duration is lengthy (6-48 weeks), not always successful, and multiple non-fungal mimics exist. 2, 7

Do not overlook occupational counseling—patients with chronic moisture exposure need guidance on protective measures like wearing gloves while cleaning. 3

Inadequate specimen collection from superficial nail plate rather than proximal subungual debris contributes to false negatives. 3

Assuming fungal infection in immunocompromised patients—proximal subungual onychomycosis in HIV, immunosuppression, or diabetes requires different management considerations. 2

Ignoring family member examination—household transmission is common, so examine parents and siblings for onychomycosis and tinea pedis. 5