In a 66-year-old man with a 1.5‑week history of dorsal left hallux pain that worsens with walking, is relieved by ibuprofen, has a normal visual examination, and has advanced onychomycosis, what are the most likely etiologies and first‑line management?

Dorsal Hallux Pain with Onychomycosis: Differential Diagnosis and Management

Most Likely Diagnosis

The most likely etiology is gout (podagra) affecting the first metatarsophalangeal joint, given the acute onset, dorsal hallux location, excellent response to NSAIDs, and normal visual examination despite significant pain with ambulation. The presence of advanced onychomycosis is likely coincidental rather than causative of the acute pain syndrome.

Differential Diagnosis Algorithm

Primary Considerations (Acute Pain, Normal Appearance)

Gout (First MTP Joint)

• Classic presentation: acute onset pain at dorsal hallux with excellent NSAID response
• Pain with walking despite normal visual examination is characteristic
• 1.5-week duration fits acute gouty arthritis timeframe
• Consider serum uric acid, though diagnosis is clinical during acute attack
• Joint aspiration for monosodium urate crystals provides definitive diagnosis if presentation atypical

Sesamoiditis or Stress Reaction

• Dorsal pain with ambulation in 66-year-old male
• Would expect tenderness on palpation of plantar sesamoids
• Less likely given excellent ibuprofen response suggests inflammatory rather than mechanical etiology

Early Cellulitis or Soft Tissue Infection

• The onychomycosis creates portal of entry for bacterial infection 1
• However, normal visual examination argues against this
• Onychomycosis can lead to foot ulcers, cellulitis, and gangrene, particularly in diabetic patients 1

Secondary Consideration (Related to Onychomycosis)

Symptomatic Onychomycosis

• Approximately 50% of patients with onychomycosis experience pain or discomfort 1
• About 30% have difficulty wearing footwear 1
• However, advanced onychomycosis typically presents with visible nail changes (thickening, discoloration, friable texture) 2
• The "normal appearance" of the toe makes this less likely as primary pain source

Immediate Management

For Acute Pain (Presumed Gout)

Continue ibuprofen at appropriate anti-inflammatory dosing (typically 600-800mg TID with food) given excellent response, unless contraindicated.

Consider colchicine 0.6mg BID-TID for acute gout if diagnosis confirmed and no contraindications.

Evaluate for gout risk factors: alcohol use, diuretics, chronic kidney disease, metabolic syndrome.

For Onychomycosis Treatment

Obtain mycological confirmation before initiating antifungal therapy, as approximately 50% of dystrophic nails are non-fungal 3. This is critical given the lengthy treatment duration and potential adverse effects.

Specimen collection technique 2:

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

Diagnostic testing 2:

• Potassium hydroxide (KOH) preparation with microscopy as first-line screening
• Fungal culture on Sabouraud's glucose agar to identify specific pathogen (incubate 28°C for ≥3 weeks)

Definitive Onychomycosis Treatment (Once Confirmed)

First-Line Systemic Therapy

Oral terbinafine is the preferred treatment 1, 3, 4, 5:

• Dosing: 250mg daily for 12-16 weeks for toenails 3
• Superior mycological cure rates compared to itraconazole
• Fewer drug interactions than azoles
• FDA-indicated for onychomycosis of toenail or fingernail due to dermatophytes 4

Alternative: Itraconazole 1:

• 200mg daily for 12 weeks continuously, OR
• Pulse therapy: 400mg daily for 1 week per month (3 pulses for toenails)
• Optimally absorbed with food and acidic pH
• Monitor hepatic function in patients with pre-existing abnormalities or continuous therapy >1 month

Adjunctive Measures (Essential for Success)

Mechanical debridement significantly enhances efficacy 3:

• File away as much diseased nail as possible before treatment
• Improves drug penetration
• Consider urea-based keratolytic cream to reduce nail thickness 2

Prevention of reinfection (critical given 40-70% recurrence rates) 1, 3:

• Wear protective footwear in public areas (gyms, pools, hotel rooms)
• Apply antifungal powders (miconazole, clotrimazole, tolnaftate) in shoes and on feet
• Wear cotton, absorbent socks
• Keep nails trimmed short
• Discard old footwear or decontaminate with naphthalene mothballs in sealed plastic bag for ≥3 days
• Treat all infected family members simultaneously

When Topical Therapy Alone is Appropriate

Topical antifungal lacquers should only be used as monotherapy in very specific circumstances 3:

• Superficial white onychomycosis without transverse/striate patterns
• Early distal lateral subungual onychomycosis with <80% nail plate involvement
• No lunula (nail matrix) involvement

If topical therapy indicated 3:

• Amorolfine 5% nail lacquer: once or twice weekly for 6-12 months (preferred)
• Ciclopirox 8% lacquer: once daily for up to 48 weeks (alternative)
• Must file away diseased nail material before each application

Critical Pitfalls to Avoid

Do not assume fungal infection without laboratory confirmation 2—the most common cause of treatment failure is incorrect diagnosis based solely on clinical grounds 2.

Do not use regular cosmetic nail polish during treatment 3—it creates an occlusive barrier preventing antifungal penetration and traps moisture, potentially worsening infection.

Ensure adequate treatment duration 1, 3—up to 18 months may be required for complete toenail regrowth and fungal clearance; premature discontinuation leads to high recurrence rates.

Screen for drug interactions with terbinafine 5—monitor patients taking tricyclic antidepressants, SSRIs, atypical antipsychotics, beta blockers, or tamoxifen.

Address the acute pain syndrome first—the excellent ibuprofen response and normal examination suggest the acute pain is likely unrelated to the chronic onychomycosis and requires separate evaluation for gout or other inflammatory arthropathy.