Two girls present with toenail yellowing and thickening

Case: The mother of a 5-year-old girl with syndactyly of the second and third toes (A) has noticed slowly progressive thickening and yellowing of the nail plate of her daughter’s third toe. The mother of another 5-year-old girl also notes progressive toenail thickening and yellowing—in this case, of the child’s fifth toenails bilaterally (B). 

Do both girls have onychomycosis? Are there clinical clues that can help identify the condition in addition to fungal culture?

Dermclinic–Answer

Only the child whose toes are pictured in A has onychomycosis; bilateral nail plate changes (as in B) are more likely to be the result of trauma.

The young girl with bilateral nail changes in her fifth toes (B) does not have onychomycosis. The fifth toenail is difficult to assess clinically for dermatophyte infection. This nail is often small, poorly formed, and subject to repeated trauma from footwear. However, the bilateral involvement is a clue to the cause of the changes in this child’s fifth toenails. Nail plate changes that are bilateral and symmetrical are almost always traumatic in origin and not infectious.

The girl with thickening and discoloration of her left third toenail has onychomycosis. (The nail infection is unrelated to her syndactyly.)

Workup of onychomycosis in children.
For unknown reasons, onychomycosis is an unusual occurrence in early childhood (although it is not uncommon in adolescents). Thus, I believe that children should have the diagnosis confirmed by culture before systemic therapy is prescribed. More than 90% of cases of onychomycosis are caused by the dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes.

The most important aspect of the clinical evaluation is determining whether the lunula is involved. Next, determine the percentage of the nail plate that is involved; this is broadly categorized as 25% (mild), 25% to 75% (moderate), and more than 75% (severe). Also note the number of infected nail plates.

This child has lunular involvement, and more than 75% of the third nail plate is infected. The yellowish discoloration of the lateral nail plate in her second toe suggests that this nail plate is also infected. However, the lunula of this nail cannot be observed, as is often the case in children with small nail plates.

Treatment.
In adults, lunular involvement typically represents nail matrix infection and indicates a need for systemic therapy. However, I have had a significant number of children respond to topical therapy regardless of their clinical presentation. Thus, in children—even those in whom the lunula is involved—I begin treatment with topical ciclopirox while awaiting the results of the fungal culture. If the child tolerates topical therapy, I continue this for about 3 months. Children with mild to moderate infection often respond completely in this time, and those with lunular involvement who respond to topical therapy will have a normal-appearing nail emerging from under the proximal nail fold. If a child with lunular involvement shows evidence of responding to topical ciclopirox, continue treatment until the nail is clear; this may require up to a year of daily application.

If a patient has no response to topical therapy, systemic therapy is necessary. Terbinafine, although not approved for use in children, is my first-choice systemic agent. It is administered for 3 months in a weight-based dosage protocol.¹

This child is currently being treated with topical ciclopirox. I hope to have follow-up pictures for you in the next few months.