Dermatology · Fungal Nail Infections
The facts most likely to be tested
Trichophyton rubrum is the most common dermatophyte responsible for distal subungual onychomycosis.
Clinical presentation typically involves nail plate thickening, subungual hyperkeratosis, and onycholysis with a yellow-brown discoloration.
Periodic acid-Schiff (PAS) stain of nail clippings is the most sensitive and preferred diagnostic test for confirming fungal elements.
Oral terbinafine is the first-line systemic treatment due to its superior efficacy and fungicidal activity compared to azoles.
Liver function tests (LFTs) must be monitored during systemic terbinafine therapy due to the risk of drug-induced hepatotoxicity.
Topical agents like efinaconazole or ciclopirox are reserved for mild-to-moderate cases involving less than 50% of the nail plate without matrix involvement.
Diabetes mellitus and peripheral vascular disease are significant risk factors that increase the likelihood of secondary bacterial infections like cellulitis.
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A 55-year-old male with a history of type 2 diabetes presents to the clinic complaining of unsightly toenails. Physical examination reveals thickened, yellow-brown, brittle toenails on the first and second digits of the right foot with associated subungual debris. There is no surrounding erythema or warmth, and the patient denies pain. A PAS stain of the nail clippings is performed, which confirms the presence of fungal hyphae.
What is the most appropriate first-line systemic pharmacotherapy for this patient?
Oral terbinafine
The patient presents with classic signs of onychomycosis, and oral terbinafine is the gold-standard systemic treatment, requiring baseline and periodic LFT monitoring.
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Etiology / Epidemiology
Common in elderly and diabetics; caused by dermatophytes (e.g., Trichophyton rubrum).
Clinical Manifestations
Presents as subungual hyperkeratosis and onycholysis; distal lateral subungual onychomycosis is the most common subtype.
Diagnosis
Periodic acid-Schiff (PAS) stain is the gold standard for confirming fungal elements.
Treatment
Terbinafine is the first-line oral therapy; monitor LFTs due to hepatotoxicity.
Prognosis
Recurrence is common; 12-week treatment duration is required for toenails.
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Epidemiology & Etiology
Prevalence increases significantly with age, affecting up to 50% of the elderly population. Primary pathogens are dermatophytes, specifically Trichophyton rubrum and Trichophyton mentagrophytes. Diabetes mellitus, peripheral vascular disease, and immunocompromise are major risk factors.
Pertinent Anatomy
The infection involves the nail plate, nail bed, and matrix. The hyponychium serves as the primary portal of entry for fungal pathogens. Thickening of the nail plate occurs due to the accumulation of keratinous debris in the subungual space.
Pathophysiology
Fungal invasion begins at the distal nail edge, progressing proximally toward the matrix. The fungus secretes keratinases to digest the nail plate, leading to structural degradation. Chronic inflammation results in subungual hyperkeratosis, which physically lifts the nail plate from the bed, known as onycholysis.
Clinical Manifestations
Patients present with yellow-white discoloration, nail thickening, and brittle, crumbling nail plates. Distal lateral subungual onychomycosis is the classic presentation. Rule out psoriasis if pitting or oil spots are present, as these mimic fungal infection.
Diagnosis
Clinical appearance alone is insufficient for diagnosis. The Periodic acid-Schiff (PAS) stain of nail clippings is the gold standard due to high sensitivity. Fungal culture may be used to identify the specific species if systemic therapy is planned.
Treatment
Terbinafine is the first-line oral agent for dermatophyte infections. Hepatotoxicity requires baseline and periodic LFT monitoring. Topical agents like efinaconazole are reserved for mild cases or patients who cannot tolerate systemic therapy.
Prognosis
Treatment is prolonged, often requiring 12 weeks for toenails to allow for full nail regrowth. Recurrence is frequent, especially in patients with persistent risk factors. Complications include secondary bacterial cellulitis, particularly in diabetic patients.
Differential Diagnosis
Psoriasis: presence of nail pitting and oil spots
Lichen planus: longitudinal ridging and pterygium formation
Contact dermatitis: history of allergen exposure
Trauma: history of repetitive microtrauma or acute injury
Yellow nail syndrome: associated with chronic respiratory disease and lymphedema