Dermatology & Podiatry & Family Medicine
Onychomycosis (nail ringworm)
Onychomycosis—commonly known as nail ringworm or nail fungus—is a chronic fungal infection of the nail plate and its associated structures (nail bed, matrix, hyponychium), constituting the most common nail disorder worldwide and accounting for 50 to 60% of all nail dystrophies. It affects approximately 10 to 14% of the adult population in North America, with prevalence increasing with age to reach 20 to 30% after age 60. Toenails are affected in 80 to 90% of cases—primarily the big toe—while fingernails are affected in 10 to 20% of cases, often through self-inoculation from the feet. Dermatophytes of the genus Trichophyton - mainly Trichophyton rubrum (60 to 80 % of cases) and Trichophyton interdigitale (formerly T. mentagrophytes) - are responsible for the vast majority of onychomycoses. Yeasts of the genus Candida (especially C. albicans) are involved in 5 to 10 % of cases, mainly on fingernails in people who frequently come into contact with water. Non-dermatophyte molds (Fusarium, Aspergillus, Scytalidium) are rarer (5 to 10 %) but resistant to the usual treatments. Clinical diagnosis alone is insufficient - between 30 and 50 % of nail dystrophies clinically suspected of onychomycosis are not of fungal origin (nail psoriasis, lichen planus, chronic trauma) - making mycological confirmation by direct examination and culture essential before any prolonged systemic treatment. Treatment is difficult, long (3 to 6 months for fingernails, 6 to 12 months for toenails) and imperfectly effective, with mycological cure rates of 70 to 80 % and recurrence rates of 20 to 25 % at 3 years for oral terbinafine, the reference drug.
Clinical classification and forms of involvement
| Clinical form | Description and appearance | Usual fungal agent |
|---|---|---|
| Distal and lateral subungual onychomycosis (OSDL) — the most common form (85 %) | Distal or lateral nail detachment + subungual hyperkeratosis (accumulation of crumbly keratin under the nail) + yellowish to brownish or whitish discoloration + progressive thickening of the nail plate + onycholysis (separation of the nail from its bed) + progressively extends from the distal part towards the matrix, advancing under the nail | T. rubrum (dominant) + T. interdigitale + mold (Fusarium + Aspergillus) |
| Superficial white onychomycosis (SBO) | White or yellowish spots on the surface of the nail plate + superficial brittleness + gradually extends over the entire surface of the nail + the nail bed is initially normal + may resemble traumatic leuconychia | T. interdigitale (predominant for toe OSB) + mould (Fusarium + Aspergillus for OSB hands) |
| Distal subungual onychomycosis | Whitish discoloration at the proximal part of the nail (at the base + under the proximal nail fold) + infrequent in the general population + strongly associated with immunodeficiency (HIV + transplantation + hematological disorders) + may indicate undiagnosed HIV in a young adult without other risk factors | T. rubrum predominant + Candida in immunocompromised patients |
| Total dystrophic onychomycosis | Total destruction of the nail plate + the nail is completely thickened + brittle + collapsed + often the terminal form of neglected OSDL + or a primary form in the immunocompromised + massive hyperkeratosis of the nail bed + the matrix can be affected | T. rubrum + Candida immunocompromised patients |
| Candidiasis onychomycosis (fingernails ++) | Paronychia (inflammation of the proximal nail fold - redness + swelling + pain) + proximal onycholysis + brown or greenish discoloration (greenish if secondary infection with Pseudomonas predilection for fingernails + people in prolonged contact with water (housekeepers + cooks + hairdressers) + diabetics | Candida albicans + Candida parapsilosis |
Risk factors
- General risk factors: advanced age (reduced vascularization + slower nail growth + cumulative exposure) + male sex (slight predominance) + family history of onychomycosis (genetic predisposition to dermatophyte infection) + simultaneous athlete's foot (tinea pedis) - interdigital fungal reservoir favoring nail contamination + diabetes (impaired immune defense + microangiopathy + neuropathy) + immunodepression (HIV + transplant + hematological diseases + chronic corticosteroid therapy) + poor peripheral circulation (arteriopathy)
- Behavioral and environmental risk factors : regular use of swimming pools + communal showers + sports changing rooms (barefoot walking on contaminated wet floors) + wearing of closed occlusive shoes and synthetic socks (hyperhidrosis + maceration) + intensive sports activities (repeated microtrauma to the nails) + prolonged contact with water and detergents (candidal onychomycosis of the hands)
Mycological confirmation — essential examination before oral treatment
- Nail scraping clean the nail with alcohol 70 % + cut and scrape the most damaged areas (distal edge + junction area between healthy and infected nail) + subungal hyperkeratosis is the area richest in fungal elements + avoid very distal areas, which are often necrotic without viable fungi + sufficient quantity (at least 50-100 mg) of nail clippings and scrapings to remove the fungi.nail hyperkeratosis is the area richest in fungal elements + avoid very distal areas which are often necrotic without viable fungi + sufficient quantity (at least 50-100 mg of nail clippings and subungual debris) + transport to the laboratory in a dry tube or paper envelope (do not use a wet tube, as it promotes denaturation)
- Direct microscopic examination (KOH): keratin clearing with KOH 20-40 % + visualization of mycelial filaments (hyphae) + spores + results in 30 minutes to a few hours + sensitivity 80-90 % + specificity 70-80 % + confirms the presence of a fungus but does not identify the species
- Fungal culture : inoculation on Sabouraud medium + incubation at 25-28°C for 4 to 6 weeks + allows precise identification of genus and species (dermatophyte + Candida + mould) + guides choice of treatment (non-dermatophyte moulds = resistant to terbinafine) + sensitivity 50-70 % (frequent false negatives if nail very keratinized or culture insufficiently prolonged)
- Fungal PCR : molecular method for rapid and accurate identification of the species within 24-48 hours + higher sensitivity than culture (85-95 %) + available in certain reference laboratories + higher cost + indicated if non-dermatophyte mold is suspected + or direct examination-culture discrepancy + or treatment failure
- Dermatoscopy: non-invasive examination by hand (magnification × 10-16) + dermatoscopic characteristics suggestive of onychomycosis: «spike» appearance (small yellowish spicules at the proximal edge of the onycholysis) + longitudinal striations + friability of the edge + can guide the diagnosis before mycological sampling + does not replace microbiological confirmation.
ℹ️
Nail psoriasis is the primary differential diagnosis for onychomycosis—it can produce exactly the same clinical presentation (onycholysis + subungual hyperkeratosis + thickening + discoloration) and is estimated to affect 3 to 5% of the general population. A patient treated for onychomycosis with terbinafine for 3 months without any improvement should prompt a reevaluation of the diagnosis—mycological confirmation via culture should have been obtained prior to treatment. Both conditions can coexist in the same patient, further complicating clinical interpretation.
Antifungal treatment
| Treatment | Terms and Protocol | Efficacy and adverse effects |
|---|---|---|
| Oral terbinafine (Lamisil®) — first-line treatment for dermatophytes | 250 mg orally 1x/day + duration: toenails 12 weeks (3 months) + fingernails 6 weeks (1.5 months) + alternate pulse regimen (less used): 500 mg/day x 1 week/month x 3-4 months + fungal squalene epoxidase inhibitor → toxic squalene accumulation for the fungus | Mycological cure rate: 70–80% at 1–3 weeks for toenails + 80–90% at 1–3 weeks for fingernails + greater efficacy against dermatophytes + low activity against Candida and ineffective against most molds + side effects: nausea + diarrhea + headaches + rare hepatotoxicity (1 in 50,000 — liver function tests recommended if treatment lasts > 6 weeks) + taste disturbances (dysgeusia — 1–3%) + drug interactions (CYP2D6 inhibitor — increases concentrations of certain beta-blockers + antidepressants + antiarrhythmics) |
| Itraconazole (Sporanox®) — alternative or if Candida | Continuous regimen: 200 mg/day x 12 weeks (toes) + or 200 mg/day x 6 weeks (hands) + pulse regimen (recommended): 400 mg/day x 1 week/month x 3 months (toes) or x 2 months (hands) + CYP3A4 and CYP2C9 inhibitor → very numerous drug interactions | Overall efficacy comparable to terbinafine but slightly lower for dermatophytes + superior for Candida + side effects: nausea + abdominal pain + hepatotoxicity + major drug interactions (many drugs contraindicated or to be monitored) + congestive heart failure (contraindicated in CHF) + reimbursed by RAMQ according to criteria |
| Amorolfine (Loceryl®) antifungal varnish - topical treatment | Apply 5% amorolfine nail lacquer + apply to the previously filed nail 1 to 2 times per week + minimum duration of 6 months (hands) to 12 months (toes) + inhibitor of fungal Δ14-reductase and Δ8→Δ7 isomerase + penetrates the nail bed and persists in the nail plate | As monotherapy: effective for mild to moderate cases without matrix involvement (less than 50–60% of the affected nail surface + healthy matrix) + mycological cure rate of 40–60% + in combination with oral terbinafine: improved cure rates by 15–20% compared to terbinafine alone + good local tolerance + no systemic effects + available over the counter at pharmacies + partially reimbursed by some private insurance plans |
| Ciclopirox nail polish (Penlac®) — alternative topical treatment | 8% ciclopirox lacquer + daily application + weekly trimming + minimum duration of 12 months + mechanism: chelation of metal ions (Fe³⁺ + Al³⁺) essential for fungal enzymes | Modest mycological cure rates with monotherapy (29–36% % depending on the study) + insufficient efficacy for severe forms + good safety profile + an option for patients who cannot receive oral therapy (liver failure + drug interactions + refusal of systemic therapy) |
| Efinaconazole solution (Jublia®) — triazole varnish | 10% efinaconazole topical solution + daily application to the nail and hyponychium × 48 weeks + fungal 14-α-demethylase (CYP51) inhibitor + improved penetration into the nail due to its low keratin affinity | Mycological cure rate: 55–63% (%) + complete cure rate: 15–18% (%) in pivotal trials + superior to ciclopirox varnish + significantly greater efficacy than ciclopirox + good local safety profile + high cost + available in Canada + not covered by RAMQ at the time of writing |
Prevention of relapse and hygiene measures
- Concurrent treatment of athlete's foot (tinea pedis): always treat interdigital tinea pedis simultaneously (antifungal cream - terbinafine cream 1 % × 1 week + or clotrimazole × 4 weeks) → untreated athlete's foot is the main reservoir of onychomycosis relapse
- Disinfection of shoes and the environment: spray antifungal powder (miconazole + tolnaftate) in shoes + wear flip-flops in swimming pools + changing rooms + communal showers + wash socks at 60°C or use an antifungal textile spray
- Foot hygiene: careful drying between the toes after showering (tinea pedis area of choice) + wearing cotton or breathable socks + rotating shoes to allow them to dry completely + trimming nails straight and short + filing thickened nails
- Treatment of family members : household members showing signs of tinea pedis or onychomycosis should be treated simultaneously to avoid cross-contamination → avoid sharing towels + shoes + pedicure instruments
Situations requiring prompt medical attention
Consult a doctor quickly if an onychomycosis is accompanied by pain, purulent discharge, surrounding nail cellulitis (redness spreading beyond the nail), or fever in a diabetic patient—fungal nail infections can promote bacterial superinfection and represent an entry point for cellulitis or osteomyelitis in patients with neuropathy or arteriopathy. Similarly, proximal subungual onychomycosis in a young adult without obvious risk factors should prompt HIV serology.
For mycological confirmation by nail scraping, the prescription of appropriate systemic antifungal treatment, and monitoring of therapeutic efficacy, Clinique Omicron offers medical consultations at its service points in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Clinique Omicron's medical doctors and Nurse Practitioners (NPs) clinically diagnose onychomycosis and through mycological sampling, prescribe oral (terbinafine or itraconazole) or topical (amorolfine + efinaconazole) antifungal treatment based on the clinical presentation and patient profile, monitor therapeutic response, and refer to dermatology for atypical or resistant forms. Consultations are available at several service locations in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for medical or dermatological advice. Mycological confirmation by direct examination and culture is essential before any prolonged systemic antifungal treatment to avoid treating a non-fungal nail dystrophy (nail psoriasis + lichen planus + trauma) with unnecessary and potentially hepatotoxic medications.
Omicron Clinic
Need to consult a doctor?
Treatment within 24-48 hours. In-clinic or telemedicine, anywhere in Quebec.
Insurance receipts. 7j/7. No family doctor required.