Nail disorders in infants and children: Acquired nail diseases

INTRODUCTION — Nail disorders in children can be broadly classified as congenital/inherited or acquired. The latter include trauma-induced, infectious, and inflammatory disorders, and tumors. They are benign in most cases but may be a cause of concern for parents and caregivers [1,2].

This topic will discuss the clinical features, diagnosis, and treatment of the most common acquired nail disorders in children. Congenital and inherited nail disorders in children are discussed separately. An overview of nail disorders in adults, nail surgery, and nail biopsy are also discussed separately.

●(See "Nail disorders in children: Congenital and hereditary nail diseases".)

●(See "Overview of nail disorders".)

●(See "Nail biopsy: Indications and techniques".)

●(See "Principles and overview of nail surgery".)

EPIDEMIOLOGY — Nail disorders are relatively uncommon in children, accounting for approximately 3 to 11 percent of pediatric dermatology consultations [3,4]. Data on the prevalence of specific nail disorders in pediatric populations are lacking. In one study, the prevalence of onychomycosis among patients attending a pediatric dermatologic clinic was 1.1 percent [5,6].

ANATOMY OF THE NAIL UNIT IN CHILDREN — Understanding nail anatomy is key to the recognition and management of nail diseases (picture 1) [7]. (See "Overview of nail disorders", section on 'Anatomy and physiology of the nail unit'.)

In newborns, the nails are thin and soft but completely formed. The normal fingernails are oval or rectangular in shape, with a longitudinal major axis, and flat. In many cases, the lunula is not visible. The toenails often have a trapezoid shape, with the distal width greater than the proximal.

The growth of the nail plate is continuous throughout life. The growth rate increases throughout infancy, peaks at the age of 10 to 14 years, and then becomes similar to that of young adults (1 to 1.5 mm/day) [8].

TRAUMA-INDUCED NAIL DISORDERS

Finger sucking, nail biting, onychotillomania — In newborns, nail changes, including thinning and pterygium (extension and adherence of the proximal nail fold to the nail bed secondary to scarring of the nail matrix), can occur secondary to the formation of sucking blisters on the dorsal surface of fingers in utero [9]. (See "Vesicular, pustular, and bullous lesions in the newborn and infant", section on 'Sucking blisters'.)

In young children and adolescents, nail biting (onychophagia) is common. It is estimated that over 30 percent of children older than seven years and 45 percent of adolescents are nail biters [1,10].

Clinical findings resulting from chronic nail biting include dystrophic nail changes, damage of periungual tissues, distal ingrowing of the nail plate, and progressive nail shortening [11]. Complications include acute paronychia, bacterial and viral infections, and intraoral injuries and infections [12].

Onychotillomania (nail picking disorder) is characterized by repeated picking or manicuring of the nails that results in shortening and dystrophy of the nail plate. (See "Skin picking (excoriation) disorder and related disorders", section on 'Nail picking disorder'.)

Punctate leukonychia — Punctate leukonychia (white spots on the nail plate) is typically seen in toddlers and young children. It is due to mild, traumatic injury to the distal matrix, which results in defective keratinization of the nail plate [8]. The white spots correspond to clusters of parakeratotic cells (keratinocytes with retained nucleus) within the nail plate, which alter the light reflection properties of the nail.

Punctate leukonychia resolves spontaneously without treatment as the nail grows.

Retronychia — Retronychia is an uncommon disorder of the great toenail characterized by the ingrowth of the proximal nail plate into the proximal nail fold and the stacking of multiple generations of nail plates beneath the proximal nail fold (picture 2) [13,14]. Although predominantly described in adults, retronychia has also been reported in children younger than 12 years and adolescents [15].

Retronychia is caused by a continued, usually minor trauma to the toenail that interrupts the continuity between the nail matrix and the nail plate. In contrast with onychomadesis, where the new nail growing from the matrix pushes the old nail plate forward (which is ultimately shed), in retronychia, the new nail pushes the old one upward and backward, interrupting the longitudinal growth of the nail. Several nail plates pile up under the proximal nail fold, resulting in inflammation and formation of granulation tissue. Pain and difficulty in walking are commonly reported symptoms.

Nail avulsion provides definitive treatment. However, conservative treatment with high-potency topical corticosteroids for several weeks is a reasonable initial treatment in children [15-19].

INFLAMMATORY DISEASES

Nail psoriasis — Nail involvement has been reported in approximately 15 to 60 percent of children with psoriasis and is generally unrelated to the type of psoriasis, duration, or severity [20-25]. Occasionally, nail lesions may be the sole manifestation of the disease. (See "Psoriasis in children: Epidemiology, clinical manifestations, and diagnosis".)

●Clinical presentation and diagnosis – Nail lesions generally appear at the age of 7 to 12 years. Changes are usually mild and frequently go unnoticed. In very young children, a gradual thickening of one of several toenails may be a presenting sign (picture 3). In older children, common nail abnormalities include:

•Pitting – Mild pitting of fingernails is the most common sign, occurring in up to 90 percent of affected children. Psoriatic pits are typically large and irregular in shape and distribution (picture 4). Pitting is usually limited to one or a few digits, and it is only rarely associated with other signs of nail psoriasis [21,26].

•Onycholysis – Onycholysis, often associated with subungual hyperkeratosis, is the second most common sign of nail psoriasis in children (picture 5). It typically involves several nails and is an important diagnostic clue. The salmon-pink, erythematous border ("oil drop sign" (picture 6)) that usually surrounds the onycholytic area in psoriasis may be absent or scarcely visible in children.

•Trachyonychia – Trachyonychia ("rough nails") or twenty-nail dystrophy (picture 7) may be a sign of nail psoriasis in children [27].

•Splinter hemorrhages – Splinter hemorrhages are common and are favored by trauma [21].

The diagnosis is straightforward in children with typical nail changes, especially in those who also have skin manifestations of psoriasis. In patients with subtle, isolated onycholysis, nail dermoscopy (onychoscopy), which allows for the examination of the nail with high magnification, can be helpful for detecting subclinical signs of nail psoriasis. As an example, enlarged, twisted capillaries in the nail bed, similar to those seen in cutaneous psoriatic plaques, appear as red dots on examination with a handheld dermatoscope (picture 8) [28,29]. (See "Dermoscopy of nonpigmented nail lesions", section on 'Differential diagnosis of onycholysis'.)

Conditions causing onycholysis and subungual hyperkeratosis that can be confused with nail psoriasis include mainly distal subungual onychomycosis and eczema. A potassium hydroxide (KOH) preparation of subungual debris scrapings is appropriate in most patients with subungual hyperkeratosis to exclude onychomycosis. (See "Onychomycosis: Epidemiology, clinical features, and diagnosis", section on 'Potassium hydroxide preparation'.)

●Treatment and prognosis – Topical agents, including topical corticosteroids, topical calcineurin inhibitors, topical retinoids, and vitamin D analogues, are first-line treatments for nail psoriasis in children [30]. Tacrolimus 0.1% ointment, tazarotene 0.05% cream, or vitamin D analogues can be applied once daily for five days per week (eg, on weekdays) in combination with a topical corticosteroid twice weekly (eg, on weekends). Topical agents are applied at bedtime. Wearing cotton gloves at night can prevent finger sucking and the potential ingestion of topical drugs.

Intralesional steroids may be used in older children and teenagers who are cooperative [31]. Systemic treatment may be needed in cases of refractory or severe disease. Among biologic drugs, etanercept, adalimumab, and ustekinumab are approved for administration in children [32]. (See "Nail psoriasis", section on 'Treatment'.)

Studies suggest that the involvement of the nails in pediatric psoriasis is an important predictor of psoriasis severity over time [33,34]. Whether nail psoriasis is associated with an increased risk of psoriatic arthritis in children remains uncertain. In a United States study of 181 children with plaque psoriasis, psoriatic arthritis was reported with similar frequency in children with and without nail involvement (13 and 9 percent, respectively) [23]. In contrast, a cross-sectional French study of 313 hospitalized patients younger than 18 years with psoriasis found a higher prevalence of psoriatic arthritis in children with nail psoriasis compared with those without (7.9 versus 2.4 percent) [20]. However, because psoriatic arthritis and nail psoriasis are both associated with more severe disease, the independent role of nail involvement as a predictor of psoriatic arthritis remains unclear.

Parakeratosis pustulosa — Parakeratosis pustulosa is a chronic pediatric nail disorder associated with multiple inflammatory skin conditions, including psoriasis, atopic dermatitis, and contact dermatitis [35]. It is usually limited to one digit (most often the thumb or the index finger), which shows mild, psoriasiform changes (eg, distal or lateral subungual hyperkeratosis, distal onycholysis) more marked on one side of the nail (picture 9). In most patients, nail signs are associated or preceded by an acute, inflammatory episode with erythema, scaling, and vesicles of the fingertip that evolves over time to nail dystrophy.

In most cases, parakeratosis pustulosa spontaneously regresses, but it may evolve into nail psoriasis.

Atopic dermatitis — Atopic dermatitis involving the dorsal hands and periungual tissues (picture 10) may be associated with inflammation of the nail matrix, resulting in dystrophic nail changes, most frequently transverse ridges and grooves, nail pitting, koilonychia, and trachyonychia [36,37].

Nail lichen planus — Lichen planus is an autoimmune skin disorder that may affect the skin, nails, or mucous membranes [38] (see "Lichen planus"). Nail lichen planus occurs in approximately 14 to 20 percent of children with cutaneous lichen planus, with a male predilection [39-42].

●Clinical features and diagnosis – Nail lichen planus typically presents with nail plate thinning with longitudinal ridging, fissuring, and distal splitting involving one or multiple nails (picture 11). Occasionally, lichen planus may present in children with trachyonychia (twenty-nail dystrophy) [43]. Nail bed involvement with mild onycholysis and subungual hyperkeratosis is another possible presentation. Dorsal pterygium (a V-shaped extension of the proximal nail fold into the nail bed, which divides the nail plate into two parts), secondary to an irreversible damage to a portion of the nail matrix, is rare in children. Permanent anonychia is also rare.

The diagnosis of nail lichen planus is suspected based on the typical clinical findings. Onychoscopy can support the clinical diagnosis, as it enhances the visualization of the longitudinal fissures of the nail plate typical of nail lichen planus [44-46]. However, a nail matrix biopsy is often needed to confirm the diagnosis.

●Treatment and prognosis – Early treatment is recommended to prevent irreversible nail damage [43]. The treatment approach is selected based on the age of the child, number of affected nails, severity of nail changes, and presence of concomitant lichen planus in other body areas [47].

•In older children (>14 years) and young adults with lichen planus that involves one to three nails, intralesional injections of triamcinolone acetonide are the first-line treatment. They require local anesthesia and are generally well tolerated [31]. Triamcinolone acetonide in concentrations of 2.5, 5, or 10 mg/mL, depending on disease severity, is injected monthly for five to six months to achieve visible improvement. Hematomas and transient numbness of the distal digit are common adverse events. Atrophy can be easily avoided by using an appropriate technique [47].

•In younger children and in children with more than three nails involved, severe disease, or lichen planus involving the nail bed, intramuscular triamcinolone 0.5 to 1 mg/kg monthly for at least three to six months is an alternative to intralesional therapy. Oral corticosteroids may also be a treatment option, but their use is limited by the risk of adverse effects [47].

The efficacy of intralesional or systemic corticosteroids has not been evaluated in clinical trials. Evidence for efficacy is mainly based on small, observational studies and expert consensus [47]. In the authors' experience, corticosteroids, either intralesional or systemic, are effective in achieving arrest of progression or total or partial regression of nail symptoms in approximately two-thirds of patients. Fingernails respond more and quicker than toenails, which may remain thicker for a long time. Unfortunately, relapses occur in approximately 60 percent of patients [48].

Second-line therapeutic options for patients who do not respond to systemic steroids include oral retinoids [49,50], systemic immunosuppressors, antimalarials [51], and dapsone [52]. However, these treatments have not been evaluated in children.

Nail lichen striatus — Nail lichen striatus is rare and almost exclusively seen in children between the ages of 4 months and 15 years [53]. (See "Lichen striatus".)

●Clinical features and diagnosis – Nail lichen striatus typically involves one nail and presents with longitudinal ridging restricted to the medial or lateral portion of the nail plate (picture 12). Other findings include longitudinal fissuring, onycholysis, and distal splitting. Cutaneous lichen striatus is usually present proximally to the involved nail, with red, pink, or skin-colored, flat-topped papules arranged in a linear band distributed along the Blaschko lines (picture 13). Nail changes generally appear a few weeks after the initial skin lesions but occasionally may be the only clinical manifestation of lichen striatus [54].

The diagnosis of nail lichen striatus is usually clinical. Dermoscopy can be useful to support the diagnosis, as it allows for an enhanced visualization of longitudinal ridges, fissures, and distal splitting of the nail plate and may show red spots in the lunula, corresponding to inflamed matrix areas [55]. A nail biopsy, although not routinely performed, may be necessary if the diagnosis is in doubt (eg, multiple digits affected, lack of concurrent skin lesions).

●Treatment and prognosis – Due to its self-limiting course and benign nature, treatment is generally not needed. Nail changes resolve spontaneously in 6 to 12 months in most cases, but they may also last for a few years [54,56].

In a few cases, topical corticosteroids and topical calcineurin inhibitors have been beneficial for hastening the resolution [57]. Intralesional corticosteroid injections are a possible option for long-standing, severe forms [53].

Alopecia areata — Nail changes occur in nearly 50 percent of children with alopecia areata and are usually associated with severe disease [58,59]. (See "Alopecia areata: Clinical manifestations and diagnosis".)

●Clinical features and diagnosis – Pitting is, by far, the most common nail change in children with alopecia areata [58]. Nail pits are typically regular in size and shape and are arranged in a geometric, grid-like pattern (picture 14) [59]. Other findings include trachyonychia (see 'Trachyonychia' below); geometric, punctate leukonychia; Beau's lines; and red lunula [26,60].

●Treatment and prognosis – Topical, intralesional, and systemic corticosteroids are the treatments of choice, depending on the severity of nail changes and age of the patient [31,58]. Although nail involvement is considered a risk factor for refractory alopecia areata, the clinical outcome of nail disease may not parallel that of hair loss.

Trachyonychia — Trachyonychia ("rough nails") is caused by mild inflammation of the proximal nail matrix and is characterized by rough, brittle nails with excessive longitudinal ridging. Although trachyonychia may be associated with inflammatory skin diseases, including alopecia areata, lichen planus, atopic dermatitis, and psoriasis, it is most often idiopathic in children and follows a benign, self-limited course [27].

●Clinical presentation and diagnosis – Trachyonychia may affect one, a few, or all nails ("twenty-nail dystrophy"). The affected nails typically show diffuse roughness with longitudinal and regular striations and are usually opaque with a sandpaper appearance (opaque trachyonychia (picture 15)). Less commonly, trachyonychia presents with diffuse, closely aggregated, small, superficial pits that reflect light, which gives the nail a shiny appearance (shiny trachyonychia) [61]. Nail thinning with koilonychia and cuticle hyperkeratosis may be associated.

The diagnosis is usually clinical. History and/or concomitant presence of clinical signs of inflammatory skin diseases suggest the etiology. The precise diagnosis of isolated trachyonychia may require a nail matrix biopsy. However, a nail biopsy is generally not recommended due to the benignity of the disease and its good prognosis.

●Treatment and prognosis – Idiopathic trachyonychia improves spontaneously over two to six years [27]. Thus, treatment is generally not required [27]. However, for patients who desire treatment, therapeutic options include keratolytics; topical or oral retinoids; and topical, intralesional, or oral corticosteroids.

Ingrown nails — An ingrown toenail (onychocryptosis) occurs when the nail plate edge grows into the lateral nail fold, resulting in a foreign body inflammatory reaction (picture 16) [62].

In infants and toddlers, ingrown nails are uncommon and usually associated with congenital hypertrophy of the lateral nail folds or congenital malalignment of the hallux nail. (See "Nail disorders in children: Congenital and hereditary nail diseases", section on 'Congenital hypertrophy of the lateral nail fold of the hallux' and "Nail disorders in children: Congenital and hereditary nail diseases", section on 'Congenital malalignment of the great toenail'.)

In adolescents and young adults, ingrown nails are the most common toenail disease, with a clear male predominance (male-to-female ratio approximately 2:1). Anatomical nail characteristics (eg, unusually wide or curved toenails) may be a predisposing factor. Triggering factors include improper nail trimming (eg, cutting away the distal lateral nail edges), tight-fitting shoes, hyperhidrosis, and trauma.

●Clinical features and diagnosis – Ingrown toenails have been classified into three clinical stages, based on clinical findings and severity [63]:

•Mild (stage 1) – The lateral nail plate is embedded in one or both lateral folds, which become swollen, erythematous, and painful.

•Moderate (stage 2) – Edema and erythema are complicated by secondary infection, seropurulent discharge, and formation of granulation tissue (pseudopyogenic granuloma).

•Severe (stage 3) – There is chronic inflammation with epithelialized granulation tissue and severe hypertrophy of the lateral nail folds.

●Treatment and prognosis – Conservative measures are generally recommended in cases of mild to moderate lesions. These include cotton wick insertion under the corner of the nail, dental floss technique, sleeve technique, taping procedure, and nail wiring. Surgical treatment is indicated for the most severe cases. Surgical techniques include partial nail avulsion coupled with partial surgical or chemical matricectomy, radical resection of the affected nailfold, and total nail avulsion. However, these techniques have not been evaluated in high-quality studies, and there is no consensus among experts on the technique of choice [64]. Recurrence is common [65]. (See "Ingrown nails", section on 'Management'.)

INFECTIOUS DISEASES

Onychomycosis — Onychomycosis is uncommon in children [5,6,66,67]. In a systematic review of 34 studies, the pooled worldwide prevalences of dermatophyte and yeast onychomycosis in children were 0.14 and 0.09 percent, respectively [66]. Trichophyton rubrum is the most common etiologic agent [68,69]. Predisposing factors include male sex, concurrent tinea pedis, dermatophyte infection in other family members, nail abnormalities, traumatic factors, and immunodepression. (See "Onychomycosis: Epidemiology, clinical features, and diagnosis" and "Onychomycosis: Management".)

●Clinical features and diagnosis – The most common type of dermatophyte onychomycosis is distal subungual onychomycosis. It presents with onycholysis, subungual hyperkeratosis, and yellowish discoloration (picture 17). Less commonly, onychomycosis may present as proximal subungual onychomycosis or white superficial onychomycosis. Candida species may invade the nails in predisposed children (mainly newborn or immunodepressed children), resulting in total onychomycosis with paronychia [70].

Laboratory tests (ie, potassium hydroxide [KOH] preparation and fungal culture) are needed to confirm the diagnosis [70]. Nail dermoscopy (onychoscopy) can help in differentiating clinical onychomycosis from other conditions that cause onycholysis (eg, trauma, nail psoriasis) and guide the decision to perform mycology tests. Dermoscopy can also help identify the best spot to obtain adequate samples for mycologic examination [71]. (See "Dermoscopy of nonpigmented nail lesions", section on 'Differential diagnosis of onycholysis'.)

●Treatment and prognosis – Topical antifungal agents are the first-line treatment for limited distal subungual onychomycosis (involvement of less than 50 percent of the nail plate in one to three nails) [72]. We typically use ciclopirox 8% lacquer daily or amorolfine 5% lacquer weekly for a minimum of three months [73].

Oral antifungal therapy should be considered when more than three nails are involved and when more than 50 percent of the nail plate is involved. Among antifungal agents, terbinafine has a good safety profile in children [74]. Terbinafine is given for 8 weeks for fingernails and 12 weeks for toenails.

There is limited evidence on the efficacy and safety of antifungal treatments for pediatric onychomycosis. Topical treatments may be preferred in children due to a favorable safety profile and consideration that a thinner nail plate and faster nail growth rate may increase the response rate.

•In a small, randomized trial that included 40 children with distal toenail dermatophyte onychomycosis treated with ciclopirox lacquer or vehicle for 32 weeks, mycologic cure was 70 percent in the active treatment group and 20 percent in the vehicle group [75].

•In a systematic review of seven studies (one randomized trial) examining the efficacy and safety of oral antifungal treatment in children, the pooled response rate for terbinafine (84 patients) and itraconazole (94 patients) was 80 and 79 percent, respectively [76]. However, the studies were generally of poor quality and used heterogeneous definitions of cure. Adverse events were rare and included increase of liver enzymes in one patient taking terbinafine and ataxia and fatigue in two patients taking itraconazole.

Viral infections

Ungual warts — Ungual warts are benign lesions caused by human papillomavirus (HPV) strains 1, 2, 4, 27, and 57. They are common in children older than six years, and their spread is facilitated by nail biting. (See "Cutaneous warts (common, plantar, and flat warts)".)

●Clinical features and diagnosis – Warts present as small, hyperkeratotic papules that grow over time, reaching a size of up to 10 to 20 mm. They are usually located in the proximal nail folds but can also develop under the nail plate (picture 18) [77].

The diagnosis of warts is clinical. Onychoscopy may be helpful for detecting subclinical periungual warts that are too small to be seen by the naked eye [44].

●Treatment and prognosis – Wart management is challenging due to the high rate of recurrence and risk of treatment-related nail dystrophy. Therapeutic options include topical salicylic acid, cryotherapy with liquid nitrogen, trichloroacetic acid, duct tape, cimetidine, cantharidin, podophyllin resin, and carbon dioxide (CO₂) laser [78,79]. We typically use liquid salicylic acid as first-line treatment. (See "Cutaneous warts (common, plantar, and flat warts)", section on 'Salicylic acid'.)

Intralesional injection of bleomycin is not indicated in children due to the risk of systemic absorption.

Herpetic whitlow — Herpetic whitlow (herpetic paronychia) is a viral infection of the hand caused by herpes simplex virus (herpes simplex virus type 1 [HSV-1] and herpes simplex virus type 2 [HSV-2]). It typically occurs in children who suck their fingers or bite their nails and have a primary herpetic gingivostomatitis or are asymptomatic salivary carriers. (See "Overview of hand infections", section on 'Herpetic whitlow'.)

●Clinical features and diagnosis – Herpetic whitlow typically affects one finger and presents with single or grouped vesicles with clear or cloudy content close to the nail or involving the lateral nail folds (picture 19). Accompanying symptoms include pain, swelling, and erythema. Nail bed location may rarely occur, with painful lateral onycholysis and subungual hemorrhage.

The diagnosis is in most cases clinical but can be confirmed by Tzanck smear or viral culture. Onychoscopy can be useful to detect vesicles not visible to the naked eye (eg, on periungual tissues or subungual space) [44,80]. (See "Epidemiology, clinical manifestations, and diagnosis of herpes simplex virus type 1 infection", section on 'Diagnosis'.)

The main differential diagnoses of herpetic whitlow are bacterial paronychia and bacterial felon [81].

●Treatment and prognosis – Herpetic whitlow is a benign, self-limiting disease that, in most cases, resolves without treatment in two to three weeks. Antiviral therapy (eg, oral acyclovir, valacyclovir, famciclovir) is indicated in children with recurrent lesions or in immunocompromised children who may develop disseminated disease. Oral antivirals should be administered within 48 to 96 hours of disease onset. (See "Herpetic gingivostomatitis in young children", section on 'Indications for antiviral therapy'.)

Hand, foot, and mouth disease — Hand, foot, and mouth disease (HFMD) is a common viral disease in children that typically manifests with fever and vesicles involving the hands, feet, and mouth. The disease is most frequently associated with coxsackievirus and enterovirus infection [82]. (See "Hand, foot, and mouth disease and herpangina".)

The mechanism of nail lesions is not clear but might be related to mechanical trauma (eg, finger sucking) and secondary viral infection of the nail matrix, resulting in the arrest of nail matrix proliferation [83-85].

●Clinical features and diagnosis – The most frequent nail change observed in HFMD is onychomadesis (nail shedding) of several or all nails; it typically occurs four to eight weeks after the onset of illness [84]. Beau lines and leukonychia have also been described [86].

●Treatment and prognosis – Treatment is not required because the disease has a spontaneous regression with rare sequelae. Parents and caregivers can be reassured that complete regrowth of the nail will occur in 6 to 12 weeks.

Bacterial infections

Blistering distal dactylitis — Blistering distal dactylitis is a rare, localized bacterial infection of the distal phalanx that most commonly affects children between 2 and 16 years of age. The causative organisms are group A Streptococcus, and, less commonly, Staphylococcus aureus and Staphylococcus epidermidis.

●Clinical features and diagnosis – Blistering distal dactylitis typically presents with an oval, fluid-filled blister 10 to 30 mm in diameter located on a single finger pad (picture 20A-C). Over the following days, the blister can extend to the nail folds and rupture, leaving a superficial erosion. Patients may complain of pain and a burning sensation [87,88].

The diagnosis is clinical and can be confirmed with Gram stain smear and bacterial culture of the blister fluid. The differential diagnosis includes herpetic whitlow, epidermolysis bullosa, bullous impetigo, and friction blisters [89].

●Treatment and prognosis – Tense bullae can be deflated with a sterile needle to provide pain relief and then covered with a nonadherent dressing. Empirical treatment with beta-lactamase-resistant antibiotics (eg, flucloxacillin, dicloxacillin, cloxacillin) can be started while awaiting the culture results. For patients with proven methicillin-resistant Staphylococcus aureus (MRSA) infection, oral or parenteral agents that cover local strains of MRSA are indicated [87,90]. (See "Skin and soft tissue infections in children >28 days: Evaluation and management".)

Paronychia — Acute paronychia is a painful bacterial infection of the periungual tissues caused by S. aureus and group A Streptococcus [91]. The inciting event is a mechanical lesion of the periungual skin, usually caused by trauma. Paronychia is also a frequent adverse event in children treated with BRAF and MEK inhibitor anticancer agents [92].

●Clinical features and diagnosis – Acute paronychia presents with pain, swelling, and erythema of the nail folds. Formation of pus along the paronychial fold can occasionally result in the formation of an abscess involving the hyponychium and the area below the nail plate (picture 21). Due to the fragility of the nail matrix in children, even a mild, acute paronychia may induce a permanent nail dystrophy. The diagnosis of paronychia is made clinically.

●Treatment and prognosis – Systemic antibiotics are the first-line therapy for acute paronychia without abscess in children. Empirical treatment is started with beta-lactamase-resistant antibiotics (eg, flucloxacillin, dicloxacillin, cloxacillin). Drainage is indicated if there is abscess [93]. (See "Paronychia", section on 'Treatment'.)

TUMORS

Subungual exostosis — Subungual exostosis is a benign, solitary, slowly growing osteochondroma of the toes and fingers. It is the most common nail tumor in the pediatric population, with adolescents and young adults representing 16 to 55 percent of patients [94]. The etiology is unknown, but patients often report a history of trauma.

●Clinical features and diagnosis – Subungual exostosis typically develops at the mediodorsal tip of the terminal phalanx, elevating the nail plate. It is palpated as a stone-hard tumor firmly attached to the bone with a keratotic surface that can occasionally ulcerate (picture 22) [95].

Dermoscopy may support the clinical suspicion of exostosis [44,96]. The diagnosis is confirmed by radiographic examination and histopathologic examination of the excised lesion.

The clinical differential diagnosis includes ingrown toenails, verruca vulgaris, pyogenic granulomas, glomus tumors, lipomas, fibromas, keratoacanthomas, squamous cell carcinomas, and subungual malignant melanomas [97].

●Treatment and prognosis – The first-line treatment of subungual exostosis is complete surgical resection. It is important to remove the entire lesion because recurrence after excision is estimated to occur in up to 53 percent of cases [98,99].

Fibrokeratoma — Acquired ungual fibrokeratoma is a benign fibroepithelial tumor of the nail apparatus of unknown etiology [100]. Traumatic events with consequent reactive hyperplasia have been suggested as causative factors [101]. Multiple fibrokeratomas (Koenen tumors) occur in approximately one-half of children affected by tuberous sclerosis complex and are considered a major clinical diagnostic criterion. (See "Tuberous sclerosis complex: Clinical features".)

●Clinical features and diagnosis – Fibrokeratomas usually arise from the proximal nail fold as a pedunculated lesion with a characteristic "garlic clove" shape (picture 23). They are associated with a longitudinal furrow of the nail plate due to compression of the matrix. Fibrokeratomas of the distal nail bed produce erythronychia and a subungual, filiform mass.

The diagnosis of ungual fibrokeratoma is made based on histopathologic examination of the excised lesion.

●Treatment and prognosis – Surgical excision is the treatment of choice. The recurrence rate after treatment is approximately 10 percent due to the incomplete surgical removal [99,102].

Pyogenic granuloma — Pyogenic granuloma is a relatively common, acquired, benign, vascular tumor that frequently involves the nail apparatus, including the periungual tissues and the nail bed. (See "Pyogenic granuloma (lobular capillary hemangioma)".)

The pathogenesis of pyogenic granuloma is unclear. Trauma, infection, drugs, and sex hormones associated with pregnancy are the most frequent causes. The high frequency of pyogenic granuloma around the nails is likely due to the high frequency of trauma and/or inflammation of the periungual tissues and high vascularity of the nail unit [103].

●Clinical features and diagnosis – The lesion appears as a solitary, red, pedunculated papule that is very friable and bleeds easily. Less commonly, it may present as a sessile plaque. It shows rapid, exophytic growth over weeks and often undergoes ulceration and bleeding.

The diagnosis is clinical in most cases. The main differential diagnosis is amelanotic melanoma of the nail apparatus, which is very rare in children.

●Treatment and prognosis – There is no consensus among experts on the treatment of periungual pyogenic granuloma in children. In children, we prefer a trial of topical beta-blockers (eg, topical timolol, topical propranolol) as initial therapy [104-106]. We instruct parents or caregivers to apply one drop of a topical beta-blocker to the lesion twice daily for two months. Lesions that do not respond to topical timolol are surgically excised [107].

Other therapies include pulsed dye laser, cryotherapy, cautery and electrodesiccation, chemical cauterization with silver nitrate, or imiquimod [108]. (See "Pyogenic granuloma (lobular capillary hemangioma)", section on 'Management'.)

Melanonychia — Melanonychia refers to a black-brown-gray pigmentation of the nail due to the presence of melanin within the nail plate. It may be due to melanocytic activation or melanocytic hyperplasia. (See "Longitudinal melanonychia", section on 'Melanonychia due to melanocytic activation' and "Longitudinal melanonychia", section on 'Melanonychia due to melanocytic hyperplasia'.)

●Clinical features and diagnosis – Melanonychia in children most frequently presents as a longitudinal band (longitudinal melanonychia) but may also appear as a transversal band (transversal melanonychia) or involve the entire nail plate (total melanonychia) [109,110].

•Melanonychia affecting multiple nails – When multiple nails are affected, melanonychia may represent a normal variant in populations with highly pigmented skin (ethnic melanonychia) or may be associated with hyperpigmentation syndromes, such as Peutz-Jeghers syndrome and Laugier-Hunziker syndrome. (See "Peutz-Jeghers syndrome: Clinical manifestations, diagnosis, and management" and "Acquired hyperpigmentation disorders", section on 'Laugier-Hunziker syndrome'.)

•Melanonychia affecting a single digit – In most cases, melanonychia affecting a single digit (picture 24) is due to melanocyte proliferation (nail matrix nevus or, rarely, melanoma).

-Nail matrix nevi – Nail matrix nevi may be present at birth, or they may develop at two to four years of age. They occur more frequently in fingernails (most often in the thumb) than in toenails. The nail shows a longitudinal, pigmented band whose width and degree of pigmentation varies considerably among patients. The pigmentation may be homogenously distributed, or darker bands may appear over diffuse, pale pigmentation [111]. Dark bands may be associated with the pseudo-Hutchinson sign because the dark nail plate pigmentation is visible through the transparent nail fold. Some clinical and onychoscopic features that are alarming in adults are commonly observed in children: Hutchinson sign, variation of the color of the band, triangular shape, globules, and nail dystrophy [112]. In children, it is also quite common to observe a gradual fading of the band [113]. Fading of the pigmentation, called "regressing nevoid nail melanoma in childhood," is unique to children and not indicative of regression of the nevus but just of decreased melanocytic activity of nevus cells [114,115].

-Nail melanoma – The total number of pediatric nail melanomas described in the literature is very small and consists mainly of melanomas in situ [116]. Clinical and dermoscopic signs that suggest melanoma in children are rapid evolution in growth and darkening of the color. In these cases, a nail matrix biopsy is essential for an accurate diagnosis [117]. (See "Nail biopsy: Indications and techniques", section on 'Nail matrix biopsy'.)

●Management and prognosis – The approach to treatment depends on the child's personal and family history and on the clinical and dermoscopic features of the pigmented nail band. The decision to perform a biopsy in a younger child with melanonychia is often influenced by the parents' or caregivers' anxiety. However, the benefit of potentially diagnosing a rare, subungual melanoma must be weighed against the risks associated with nail unit biopsy, including the risks of sedation, the possibility of pigment recurrence, and the possibility of permanent nail dystrophy [26]. When surgery is chosen, tangential excision of the matrix lesion is the best option [118].

SUMMARY

●Epidemiology – Acquired nail diseases, including traumatic, inflammatory, and infectious diseases and nail tumors, are uncommon in children. Although they mirror those seen in adults in most cases, a few nail disorders are only seen in children (see 'Introduction' above and 'Epidemiology' above):

●Trauma-induced – Trauma-induced nail disorders include nail biting, onychotillomania, punctate leukonychia, and retronychia. Punctate leukonychia (white spots on the nail plate) is typically seen in toddlers and young children as a result of mild trauma to the distal nail matrix (picture 2). Retronychia of the great toe (growth of the proximal nail plate into the proximal nail fold) is uncommon and can occur in older children and adolescents. (See 'Trauma-induced nail disorders' above.)

●Inflammatory diseases – Inflammatory nail diseases seen in children as well as in adults include nail psoriasis (picture 3 and picture 4 and picture 5 and picture 6), nail lichen planus (picture 11), nail alopecia areata (picture 14), and ingrown nails (picture 16). Inflammatory nail diseases that almost exclusively affect children include parakeratosis pustulosa (picture 9), nail lichen striatus (picture 12), and idiopathic trachyonychia (picture 15). (See 'Inflammatory diseases' above.)

●Infections – Distal subungual onychomycosis (picture 17) is the most common type of dermatophyte nail infection in children. Viral diseases affecting the nails and periungual tissues include viral warts (picture 18); herpetic whitlow (picture 19); and hand, foot, and mouth disease (HFMD)-associated onychomadesis (nail shedding). Bacterial infections of the nail apparatus in children include acute paronychia (picture 21) and blistering distal dactylitis (picture 20A-C). (See 'Infectious diseases' above.)

●Tumors – Tumors of the nail apparatus are rare. Among them, subungual exostosis (picture 22) is the most frequently seen in children. Other tumors include fibrokeratoma (picture 23) and pyogenic granuloma. Longitudinal melanonychia affecting a single digit represents a nail matrix nevus (picture 24) in most cases; nail melanoma is exceedingly rare in children. (See 'Tumors' above.)