Can onychomycosis (fungal infection of the nail) occur in toenails, specifically the thumbnails ( thumbnails referring to the nails on the toes, also known as great toes) or more accurately, the great toe nails?

From the Guidelines

Yes, onychomycosis can definitely occur in thumbnails. Onychomycosis is a fungal infection that can affect any nail on the body, including both fingernails and toenails [ 1 ]. Thumbnails are commonly affected because they, like all nails, provide an ideal environment for fungal growth when exposed to moisture and warmth. The infection typically causes the nail to become discolored (yellow, brown, or white), thickened, brittle, and sometimes separated from the nail bed.

Treatment Options

Treatment options include topical antifungal medications like ciclopirox (Penlac) or amorolfine for mild cases, and oral antifungals such as terbinafine (250mg daily for 6 weeks for fingernails) or itraconazole (200mg twice daily for 1 week per month, for 2 months) for more severe infections [ 1 ]. Complete treatment of thumbnail fungal infections often takes several months because nails grow slowly and the medication needs time to eliminate the infection as the nail grows out.

Prevention

Good nail hygiene, keeping nails dry, and avoiding sharing nail tools can help prevent infection or reinfection [ 1 ]. It is essential to note that onychomycosis can have a significant impact on the quality of life of patients, causing discomfort, difficulty in wearing footwear and walking, cosmetic embarrassment, and lowered self-esteem [ 1 ].

Key Considerations

• Onychomycosis can result in disruption of integrity of the skin, providing an entry point for bacteria leading to the development of foot ulcers, osteomyelitis, cellulitis, and gangrene in diabetic patients [ 1 ].
• The presence of sensitizing fungal/dermatophytic antigens in the nail plate may predispose to other clinical conditions in subjects with onychomycosis, such as asthma/sensitization of the respiratory tract, and skin conditions, such as atopic dermatitis, urticaria, and erythema nodosum [ 1 ].

From the FDA Drug Label

The efficacy of terbinafine tablets in the treatment of onychomycosis is illustrated by the response of patients with toenail and/or fingernail infections who participated in three US/Canadian placebo-controlled clinical trials

• Onychomycosis can occur in fingernails, which includes thumbnails. The answer is yes, onychomycosis can occur in thumbnails 2

From the Research

Onychomycosis Occurrence in Thumbnails

• Onychomycosis is a fungal infection of the nail, causing discoloration and thickening of the affected nail plate 3.
• It can occur in both fingernails and toenails, but the provided studies do not specifically mention thumbnails as a common site of infection 4, 5.
• However, onychomycosis can affect any nail, including thumbnails, as it is a fungal infection that can occur in any nail plate 3, 6.
• The diagnosis and treatment of onychomycosis are crucial to prevent complications and recurrence, regardless of the nail affected 7, 5.

Diagnosis and Treatment

• Diagnosis of onychomycosis involves physical and microscopic examination, culture, and histologic evaluation using periodic acid-Schiff staining 4, 5.
• Treatment options include oral antifungals, topical treatments, and devices, with oral terbinafine being a commonly used and effective treatment 3, 4, 7.
• Combination therapy of oral terbinafine and topical ciclopirox has been shown to be more effective than oral terbinafine alone in some cases 7.
• Prevention measures, such as avoiding walking barefoot in public places and disinfecting shoes and socks, can help reduce the risk of recurrence 3, 4.