The authors herein describe several nail conditions, which the general pediatrician is likely to encounter in the course of routine practice. Because pediatric nail disorders represent a limited component of a general pediatric practice, it can be challenging for practitioners to establish expertise in the diagnosis and treatment of these conditions and to recognize when reassurance is appropriate or when referral to a specialist is necessary. This article summarizes the anatomy of the normal nail unit, as well as the evaluation and management of onychomycosis, melanonychia, trachyonychia, onychomadesis, and nail pitting.
Key points
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Before initiating treatment of onychomycosis, it is important to establish the diagnosis with confirmatory testing.
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Most cases of longitudinal melanonychia in children are benign; rare cases of melanoma in situ have been reported.
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Trachyonychia is most commonly associated with lichen planus, psoriasis, and alopecia areata.
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The onset of onychomadesis is delayed and often appears subsequent to a systemic illness causing transient arrest of the nail matrix.
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Nail pitting is a nonspecific sign that may not require therapy.
Introduction
Although pediatric nail disorders are a limited part of a general pediatric practice, it is important for practitioners to be able to recognize and treat common nail pathology and determine when referral to a dermatologist is indicated. There is a wide spectrum of congenital, inflammatory, infectious, and neoplastic conditions that may affect the nail unit in children. Some of these conditions are isolated to the nail unit, whereas others have associated mucocutaneous or systemic manifestations. Herein, we describe several frequently encountered pediatric nail changes and disorders, as well as diagnostic considerations and treatment options.
Introduction
Although pediatric nail disorders are a limited part of a general pediatric practice, it is important for practitioners to be able to recognize and treat common nail pathology and determine when referral to a dermatologist is indicated. There is a wide spectrum of congenital, inflammatory, infectious, and neoplastic conditions that may affect the nail unit in children. Some of these conditions are isolated to the nail unit, whereas others have associated mucocutaneous or systemic manifestations. Herein, we describe several frequently encountered pediatric nail changes and disorders, as well as diagnostic considerations and treatment options.
Normal nail anatomy
To understand the pathologic processes affecting the nail unit, it is important to first recognize normal anatomy. The nail unit is composed of a variety of structures, including the nail plate, nail bed, nail matrix, proximal and lateral nail folds, and hyponychium ( Fig. 1 ).
The nail plate is the hard and translucent portion of the nail unit, composed of onychocytes, which we normally clip at its free edge. It is bounded on 3 sides by the proximal and lateral nail folds. The cuticle seals the nail plate from the outside environment at the proximal nail fold. The nail matrix is located beneath the proximal nail fold and is the germinative epithelium that creates the nail plate. The nail bed represents the epithelium and connective tissue on which the nail plate rests. The hyponychium is the distal aspect of the nail unit, at the junction of the free edge of the nail plate and the nail bed.
Onychomycosis
Onychomycosis is defined as a fungal infection of the nail plate. Although it is a nail problem that dermatologists frequently encounter, it is relatively uncommon in children less than 18 years of age, with an estimated prevalence of 0.3% worldwide. The number of cases in children seems to be increasing each year. This increase is perhaps related to increased use of occlusive foot wear, communal locker rooms, public swimming pools, and inoculation from affected family members. Adolescents may develop onychomycosis more commonly than younger children, and toenails are more often affected than fingernails. Immunocompromised individuals (ie, HIV, transplant recipients) and children with Down syndrome are more likely to acquire fungal infections of the nail.
Onychomycosis can be caused by dermatophytes (Trichophyton species, Microsporum species, Epidermophyton species), as well as nondermatophyte molds and Candida. Trichophyton rubrum is the most common cause of onychomycosis. There are several types of onychomycosis described in the literature:
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Distal lateral subungual onychomycosis
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Proximal subungual onychomycosis
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Superficial white onychomycosis
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Candida onychomycosis
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Endonyx onychomycosis
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Total dystrophic onychomycosis
The most common type of onychomycosis seen in children is distal lateral subungual onychomycosis, characterized by yellow discoloration of the nail plate, subungual debris, onycholysis (separation of the nail plate from the nail bed), and thickening of the distal and lateral aspects of the nail plate ( Fig. 2 ). The fungus typically derives from the plantar skin and infects the nail via the hyponychium and nail bed. Proximal subungual onychomycosis and superficial white onychomycosis are observed much less frequently. Both can present with leukonychia (white discoloration of the nail). Superficial white onychomycosis results from infection of the dorsal nail plate, whereas the proximal subungual variant is secondary to fungal penetration from the proximal nail fold into the deep proximal aspect of the nail plate and has also been postulated to be caused by systemic spread. Candida onychomycosis is rare, classically occurs in patients with chronic mucocutaneous candidiasis, and often presents in association with a paronychia. Endonyx onychomycosis is characterized by nail plate pigmentation, pitting, milky-white patches, and transverse indentations. Total dystrophic onychomycosis, resulting from infection of the entire nail plate, is the most severe variant and is extremely rare in children.
It is essential to remember that fungal infections of the nail can be pigmented and can mimic melanocytic lesions. Furthermore, several conditions other than onychomycosis may lead to dystrophy of the nails, including trauma, psoriasis, lichen planus, alopecia areata, atopic dermatitis or eczema, and congenital nail dystrophies. Consequently, a complete physical examination of the skin and oral mucosa should be performed to evaluate for associated cutaneous findings.
Establishing the diagnosis of onychomycosis before initiation of treatment is of paramount importance. Systemic antifungal medications have the potential for serious adverse effects. There exists a variety of methods to obtain laboratory confirmation of onychomycosis, including histologic examination of nail clippings (fixed in formalin) stained with periodic acid-Schiff or Grocott methenamine silver ( Fig. 3 ), mycologic culture, and direct microscopy with potassium hydroxide preparation. PCR is a method to diagnose onychomycosis, which may have a greater role in the future, but is currently not widely available. Before submitting a specimen for fungal culture, the target nail should be cleansed with an alcohol swab or with soap and water. The nail is then clipped back to the mycelial front (the most active area of infection), which lies at the most proximal aspect of the junction between the nail bed and nail plate that remains intact. Hyperkeratotic material can be removed from this exposed area for culture and/or microscopy. Submitting small nail clippings from the distal free edge of the nail plate are of low yield and often contain contaminants. There are several advantages and disadvantages to each diagnostic method ( Table 1 ). A negative test result does not necessarily rule out onychomycosis and may be the result of sampling error.
| Diagnostic Test | Advantage | Disadvantage | Technique |
|---|---|---|---|
| Histology (PAS) |
|
| Perform nail clipping and place specimen in formalin |
| Fungal culture |
|
| Clean the nail, clip back free edge of nail plate, collect hyperkeratotic material and submit for fungal culture |
| KOH prep |
|
| Clip back free edge of nail plate, collect hyperkeratotic material and place it on glass slide, add KOH, and interpret with microscope |
The management of onychomycosis should take into consideration patient age, the causative pathogen, cost-effectiveness, and drug-drug interactions. To date, no medication is approved by the Food and Drug Administration for the treatment of onychomycosis in children ( Table 2 ). The gold standard treatment of onychomycosis is oral antifungal therapy, with the literature supporting the use of oral itraconazole or terbinafine in children with similar efficacy and safety as adults. Oral fluconazole and griseofulvin do not appear to be as effective. Under certain circumstances, topical therapy can be used as an alternative, particularly in the setting of superficial white onychomycosis or mild to moderate subungual onychomycosis without onycholysis or matrix involvement. A recent study by Friedlander and colleagues demonstrated the efficacy of topical ciclopirox in the pediatric age group for onychomycosis.
| Antifungal | Dosage | Duration of Therapy | |
|---|---|---|---|
| Oral terbinafine | Continuous therapy | ||
| <20 kg | 62.5 mg/d | Toenails: 12 wk Fingernails: 6 wk | |
| 20–40 kg | 125 mg/d | ||
| >40 kg | 250 mg/d | ||
| Oral itraconazole | Pulse therapy a | ||
| <20 kg | 5 mg/kg/d | Toenails: 3 pulses Fingernails: 2 pulses | |
| 20–40 kg | 100 mg/d | ||
| 40–50 kg | 200 mg/d | ||
| >50 kg | 200 mg twice daily | ||
| Continuous therapy | |||
| <50 kg | 5 mg/kg/d | Toenails: 12 wk Fingernails: 6 wk | |
| >50 kg | 200 mg/d | ||
| Oral fluconazole | Intermittent therapy | ||
| 3–6 mg/kg once per wk | Toenails: 18–26 wk Fingernails: 12–16 wk | ||
| Topical ciclopirox 8% nail lacquer , b | Apply once daily to all affected nails | Toenails: 12 mo Fingernails: 6 mo | |
| Topical amorolfine 5% nail lacquer , b , c | Apply once or twice weekly to all affected nails | Toenails: 9–12 mo Fingernails: 6 mo | |
a 1 pulse = 1 week on treatment, 3 weeks off treatment.
b Duration of therapy is based on adult data. Duration may be shorter for infants and young children.
Melanonychia
Melanonychia refers to brown or black pigmentation of the nail caused by melanin deposition ( Fig. 4 ). It most commonly presents as a longitudinal streak (longitudinal melanonychia), but can also present as a transverse band (transverse melanonychia) or involve the entire nail plate (total melanonychia). Increased melanin production within the nail matrix will result in subsequent incorporation of melanin into the nail plate. Melanonychia can involve a single nail or multiple nails. When multiple nails are involved, one should consider the possibility that it is a normal variant, particularly in the setting of dark-skinned patients, or that it represents a manifestation of an underlying syndrome (ie, Peutz-Jeghers syndrome, Laugier-Hunziker syndrome) or medication-induced pigmentation (ie, hydroxyurea, minocycline, zidovudine, antimalarials, cancer chemotherapeutics). In contrast, when an isolated nail is involved, a neoplastic process is suspected. Typically, a pediatrician is confronted with the scenario of evaluating a single nail with pigmentation. As such, this will be the focus of discussion.
Parental anxiety around pigmentation of the nail is a reflection of their concern for possible melanoma. Melanoma of the nail unit is exceedingly rare in children. Of the cases documented in the literature, most have occurred in dark-skinned patients, with only 2 cases described in fair-skinned children. To date, all cases of melanoma presenting initially as longitudinal melanonychia in children have been pathologically determined to be melanoma in-situ.
Overwhelmingly, longitudinal melanonychia signifies a benign process in the pediatric population. In a study of 40 children with melanonychia aged less than 16 years, no malignant lesions were identified on histologic examination. The final diagnosis was benign nevus in 19 cases, lentigo in 12 cases, and melanocytic activation in 9 cases. Additional reports support these findings. Also unique to children is the concept of spontaneous regression of melanonychia. This fading of pigmentation may indicate decreased melanocyte activity.
The differential diagnosis of melanonychia includes exogenous pigment deposition (ie, topical agents or systemic medications), trauma or subungual hematoma, and pigmented bacterial or fungal infections of the nail. These conditions should be considered and ruled out in the assessment of melanonychia.
The evaluation and management of childhood melanonychia can be challenging. The practitioner must weigh the remote risk of discovering a melanoma against the risks of sedation and the potential for permanent nail dystrophy related to nail matrix biopsy. The practitioner must also consider patient and family preference. Excision would avoid long-term follow-up, which can often be anxiety provoking. As such, melanonychia should be assessed on a case by case basis. Generally, melanonychia of a single nail will require referral to a dermatologist or nail specialist.
Helpful tools for evaluation of melanonychia include nail clippings to rule out a pigmented onychomycosis, dermoscopy, and serial photographs. There are several classically concerning features to bear in mind, which if present in adults, should raise suspicion for melanoma ( Box 1 ). However, these rules do not always apply to the pediatric population, as many of these characteristics can be observed with benign melanocytic proliferations in children. For example, pediatric nail unit nevi can have associated periungual pigmentation (pseudo-Hutchinson sign), heterogeneity of pigmentation, and variation in width of the pigmented band (triangular shape of pigmentation). Unfortunately, there are no absolute criteria established to help definitively differentiate benign and malignant lesions in children on clinical grounds alone. If concerning or changing features are observed, prompt referral is warranted. Excision should be considered for histologic examination ( Fig. 5 ). There are multiple biopsy methods, depending on the origin of the pigmentation, including a nail matrix shave biopsy, lateral longitudinal excision, or a punch excision. Incisional or partial biopsies are not recommended as this negatively affects the accuracy of diagnosis and clinical follow-up of the remaining lesion.
