bubble_chart Overview

Onychomycosis (tinea unguium) refers to a disease caused by dermatophytes invading the nail plate or subungual tissue. On the other hand, nail fungal infection is caused by non-dermatophyte fungi and yeasts.

bubble_chart Etiology

Onychomycosis is often caused by Trichophyton rubrum, Trichophyton gypsum, and Epidermophyton floccosum. Other causative agents include Trichophyton schoenleinii, Trichophyton violaceum, Trichophyton tonsurans, Trichophyton roseum, and Trichophyton concentricum.

Fungal leukonychia is usually caused by Trichophyton gypsum, and occasionally by Cephalosporium, Fusarium, and Aspergillus terreus. Onychomycosis is mostly caused by other filamentous fungi, yeast-like fungi, and yeasts, commonly seen in malnourished fingernails or toenails. It has been confirmed that Candida albicans and Scopulariopsis brevicaulis can cause onychomycosis. In recent years, Candida parapsilosis and others have also been frequently identified as causative agents of onychomycosis.

bubble_chart Pathological Changes

Subungual onychomycosis is easily identified by PAS staining of the affected nail, where hyphae and arthrospores can be observed within the nail plate layers, usually confined to the lowest part of the nail plate. Onycholysis is not a characteristic feature of dermatophyte infection; rather, it results from the mechanical separation of the nail plate by the fungi growing within it. The distribution and quantity of fungi within the nail plate vary. The nail plate tissue may show slight or no signs of inflammation.

In fungal leukonychia, fungal hyphae are typically limited to the uppermost part of the nail plate and rarely extend to deeper layers. A large number of hyphae, which are larger and wider than those seen in subungual onychomycosis, can be observed in the upper part of the nail plate. Swollen clusters of hyphae and irregular arthrospores are often seen in the sections.

In onychomycosis caused by *Scopulariopsis brevicaulis*, molecular spores can often be found within the nail. Candidal onychomycosis is often accompanied by chronic paronychia, leading to structural damage of the nail and associated chronic inflammatory reactions. In onychomycosis caused by yeast, fungi can be found in the nail and its surrounding loose tissue. In nail diseases caused by other fungi, debris is present in the nail fold and nail bed, and hyphae can be seen in the sections.

bubble_chart Clinical Manifestations

Distal subungual onychomycosis: It usually starts from the sides or tip of the nail plate, initially presenting as grade I paronychia, which later becomes chronic or gradually subsides. Paronychia can cause pits or grooves on the nail surface, starting as small, distinct yellow or whitish spots that remain unchanged or gradually spread to the nail root. After the nail plate is infected, it may develop cracks, become brittle or thickened, and turn brown or black. Subungual deposits of keratin debris may accumulate. Normally, the nail bed does not participate in the keratin formation of the nail plate, producing keratin only beneath the nail plate. When the nail bed is invaded by fungi, it can be stimulated to produce soft and brittle keratin, loosening the nail and causing significant thickening of the nail plate due to keratin deposition. In contrast, candidal onychomycosis does not involve debris deposition, nor does the nail plate thicken. Since the debris and keratin in the nail bed provide abundant nutrients for fungal growth, the fungi proliferate rapidly, directly invading the hard nail plate from below and stimulating the nail bed to produce more keratin, further thickening the nail plate. Other fungi or bacteria may also invade the debris-laden areas. The nail matrix is usually unaffected, though some may exhibit grade I morphological changes and discoloration. In cases of *Trichophyton rubrum* infection, the distal nail plate becomes brittle and separates, leaving a thin groove with rough edges, and may destroy the entire nail if it spreads fully.

Fungal leukonychia, also known as superficial white onychomycosis, initially appears as small, cloudy areas on the nail plate surface, often starting as irregular dots of varying numbers near the lunula, free edge, or lateral folds. It may remain localized or spread across the entire nail. The nail surface is relatively soft, sometimes asymptomatic, and the infection can persist for years. Onychomycosis caused by *Trichophyton mentagrophytes* is more superficial, without paronychia, and presents with scaling at the nail bed folds, usually affecting only part of the nail, though it may occasionally involve the entire nail plate.

Onychomycosis caused by *Candida* is often accompanied by paronychia, starting at the lateral folds with slight pus accumulation. The overlying skin becomes red, swollen, and tender. The skin around the nail darkens, elevates, and separates from the underlying nail bed, eventually involving the entire nail plate. Fingernails are more susceptible than toenails. It is commonly seen in housewives, cooks, and those frequently exposed to water. Unlike *Trichophyton* infections, the nail plate does not soften or turn yellow. Other molds, such as *Aspergillus*, may also cause onychomycosis, with substantial subungual debris accumulation.

bubble_chart Diagnosis

The diagnosis is not difficult based on clinical manifestations, direct microscopic examination of fungi, and fungal culture. In subungual onychomycosis, the fungal content is relatively low and often located at the lowest part of the nail plate. Onychomycosis and tinea unguium often start in one nail, occurring asymmetrically, while other adjacent nails may remain normal.

bubble_chart Treatment Measures

The prevention and treatment of onychomycosis and nail fungal diseases primarily involve actively preventing and treating common fungal infections, with extra attention needed when nails are injured or malnourished.

Onychomycosis is one of the more challenging fungal skin diseases to treat, often prone to recurrence even after clinical cure. Generally, local therapy is preferred for onychomycosis and nail fungal diseases.

1. Apply 30% glacial acetic acid externally or soak the affected nail in 10% glacial acetic acid once daily for 3 to 6 months. For better efficacy, thin the affected nail before application. When applying 30% glacial acetic acid, take care to protect the skin around the nail.

2. Apply a solution of 6% salicylic acid, 12% lactic acid, 95% alcohol, 10% iodine tincture, or a 50-50 mixture of 10% lactic acid to the affected nail. The usage, treatment, and precautions are the same as above.

3. Medicated nail removal: Apply 40% urea ointment and then remove the affected nail.

Additionally, oral Sporanox (200mg) can be taken twice daily for three weeks. Take the medication for one week at the beginning of each month, then stop, and repeat the one-week course at the start of the second and third months. Lamisil can also be taken orally.

bubble_chart Differentiation

Onychomycosis should be differentiated from other skin diseases and systemic diseases that cause nail changes. For example, nail disorders such as psoriasis, congenital pachyonychia, congenital leukonychia, eczema, scleroderma, syringomyelia, Raynaud's disease, acrodermatitis continua, and exfoliative dermatitis can all cause nail alterations. These nail disorders often affect multiple nails and frequently occur symmetrically.