Nail Disorders

Abstract

Nail disorders in infants and children may be congenital or acquired. Nail signs may be present at birth or develop during neonatal life or later, and may occasionally be part of a syndrome or a systemic disorder. Nail dermatoscopy (onychoscopy) may be a useful tool for the diagnosis, management, and prognosis of different nail diseases in daily practice. In most cases it allows a better visualization of signs already evident to the naked eye. However, in a few diseases, the technique provides very important diagnostic information.

1 Technique

Nail dermatoscopy, or onychoscopy, can be performed “dry” or with “immersion” technique (in order to render the stratum corneum translucent) depending on the suspected disease: in case of nail plate alterations, it is better to use the dry method, while in case of color alterations, the use of gel is recommended because it increases visibility.

The unique anatomy of the nail apparatus makes onychoscopy technically difficult to be performed and not easy to be interpreted. The main technical problem is the convexity and hardness of the nail plate, which makes difficult to obtain complete contact of the lens to the surface. The usual technical problem to see all the nail at once is avoidable in children, in which the small size of the nail permits obtaining all the part of the nail unit in same picture.

2 Dermatoscopy of Normal Nails in Children

Onychoscopy should not be limited to the nail plate, which is only a part of the nail apparatus, but should include the proximal and lateral folds, the hyponychium, and the nail bed, the latter visible through the plate. The nails of pediatric population are thin, soft, and completely formed and their size is related to age. The normal nail is rectangular in shape: the fingernail has a longitudinal major axis and transversal minor axis, while the toenail in children has a trapezoid shape with always a longitudinal major axis and is wider at the distal free edge.

The normal nail plate is well displayed at ×10 magnification. It appears pale pink in color because of the presence of the vessels of the underlying nail bed, and its surface is smooth and shiny. It is translucent and adherent to the nail bed and with a free edge of regular thickness.

The nail bed is visible below the transparent plate and appears pale pink in color. It represents the epithelium and connective tissue on which the nail plate rests.

The normal proximal nail fold at ×10 magnification appears pale pink in color, and its epithelium has a smooth surface. The cuticle is easily visible as a transparent transverse band that seals the nail plate from the outside environment at the proximal nail fold.

The hyponychium is the distal part of the nail unit, at the junction of the free edge of the nail plate and the nail bed. It can be observed by putting the lens under the nail plate free margin: the epithelium shows the digital creases and, at ×40 magnification, the capillary of the dermis appears as red dots, due to their arrangement perpendicular to the skin.

3 Alterations of the Nail Shape

The alterations of the shape of the nails include abnormalities in size, proportion, or curvature.

3.1 Abnormal Size

Anonychia and micronychia represent the total or partial absence of the nail. They can be congenital or acquired. In nail-patella syndrome, which is due to a mutation of the gene LMX1B localized on chromosome 9q34.1 [1, 2] and is inherited in an autosomal dominant pattern, nail hypoplasia is associated with bone and kidney abnormalities. Nail changes may be limited to the fingernails, usually the thumbs, with hypoplasia or absence of the nail plate. Dermatoscopy reveals the characteristic finding of the lunula with a triangular shape with the horizontal basis of the triangle at the level of the proximal margin and the point of the triangle directed toward the distal margin. The color of the triangular lunula is white, while its dimension can be different in different digits, being more pronounced in the thumbs that usually are the more affected, and less evident going toward the fifth digit (Fig. 25.1).

Fig. 25.1

Triangular lunula in a patient affected by nail-patella syndrome. Dermatoscopy (×10): horizontal basis of the triangle at the level of the proximal margin and point of the triangle directed toward the distal margin

3.2 Abnormal Proportion

In children, alterations of nail proportion can be congenital, such as in racquet nails where the nail plate is wider than long and the nail appears abnormally broad, or acquired as in onychophagia, which affects children and adolescents who start to bite the nails possibly because of stress, anxiety, or boredom. In onychophagia the nail plate becomes shorter and irregular in shape with the transverse axis longer than longitudinal axis. Dermatoscopic features of nail biting include (a) short nail plate, with irregular distal margin and exposure of the nail bed epithelium to mechanical and chemical damage of the teeth and saliva; (b) dilated proximal nail fold capillaries due to chronic trauma; (c) scaling and crusts, wounds, and diffuse inflammation of the periungual folds, associated with hemorrhages; and (d) skin maceration on the lateral folds. Moreover, in severe cases it is possible to observe the hyponychium and nail bed skin. One or more bands of melanonychia can be associated to melanocytic activation by trauma of nail matrix (Fig. 25.2).

Fig. 25.2

Nail biting. Dermatoscopy (×10): band of melanonychia

3.3 Abnormal Curvature

The normal nail plate is curved transversally and, to a lesser extent, longitudinally. In cases of abnormal curvature of a single digit, it is important to exclude a nail bed tumor, such as osteochondroma. It usually appears between the ages of 10 and 25 years, sometimes preceded by a history of trauma and appears as a firm and tender nodule under the nail plate clinically similar to subungual exostosis. Onychoscopy of osteochondroma shows the subungual mass under the nail plate with a superficial view of the nail bed vessels that are easily visible with a reticular aspect (Fig. 25.3).

Fig. 25.3

Pseudoclubbing due to osteochondroma. Dermatoscopy (×20): longitudinally curved nail plate

4 Alterations of the Nail Surface

Different signs on the surface of the nail plate, reflecting a damage of nail matrix, can be detected.

4.1 Pits

They are small depression of the nail plate surface. Dermatoscopy is very helpful to distinguish diseases appearing with pitting, such as psoriasis and alopecia areata, especially in cases where pitting is the only sign. The pits of psoriasis are large, deep, and irregular in shape, size, and distribution (Fig. 25.4), while the pits of alopecia areata are regular in shape, size, and distribution (Fig. 25.5).

Fig. 25.4

Pitting in nail psoriasis: dermatoscopy (×20)

Fig. 25.5

Pitting in patient affected by alopecia areata: dry dermatoscopy (×10)

4.2 Beau’s Lines and Onychomadesis

Beau’s lines are transverse nail plate surface depressions resulting from a mild trauma to the proximal nail matrix with transient reduced nail growth. When the trauma is more intensive and the damage involves the whole nail matrix with a total arrest of the nail plate production, there is onychomadesis, which appears as a transverse detachment of the nail from the proximal nail fold. In children, Beau’s lines and onychomadesis can be present in one digit as a result of bacterial or viral infection or in case of traumas such as finger sucking or a habit tic. In finger sucking dermatoscopy shows onycholysis of the distal nail plate and maceration of the periungual skin due to saliva (Fig. 25.6). If the trauma from biting is at the level of the proximal nail fold, Beau’s lines can appear until onychomadesis. In habit tic nail deformity, the clinical aspect is characterized by longitudinal furrows of the nail plate with multiple transverse lines. Onychoscopy permits enhanced visualization of the typical findings of the transverse lines that are parallel from each other (Fig. 25.7). The cuticle is absent or uplifted with hyperkeratosis. The periungual tissue may show scales and crusts. Macrolunula can be associated, resulting from the periodic trauma, as well as a band of longitudinal melanonychia due to melanocytic activation.

Fig. 25.6

Finger sucking. Dermatoscopy (×20): onycholysis of the distal nail plate

Fig. 25.7

Habit tic nail deformity. Dermatoscopy (×10): multiple transversal ridging

In cases where several nails are interested by Beau’s lines and/or onychomadesis, a systemic cause should be suspected, such as coxsackievirus-induced hand-foot-mouth disease.

4.3 Trachyonychia

It is a benign inflammatory nail condition of the proximal nail matrix that can be due to many diseases including alopecia areata, lichen planus, eczema, and psoriasis. TND can affect one or all nails (“20-nail dystrophy”). The affected nails show diffuse roughness with longitudinal and regular fissuring and are usually opaque. Nail thinning with koilonychia may be present. At dry onychoscopy, the nail plate shows fine longitudinal striations covered by thin scales and mild thinning (Fig. 25.8).

Fig. 25.8

Severe trachyonychia due to alopecia areata: dry dermatoscopy (×10)

4.4 Longitudinal Furrow

It is a single longitudinal depression that runs through the nail plate from the proximal to the distal part with a variable depth and width on the basis of the disease. Longitudinal furrowing results from a compression of the nail matrix usually by a benign tumor that is visible under the proximal nail fold. In children, the most typical tumor that appears with longitudinal furrowing is fibrokeratoma, a common benign tumor of the proximal nail fold. The clinical aspect fibrokeratoma is reflected by dermatoscopy that shows a periungual filiform mass, pink in color, sometimes with a hyperkeratotic tip. When the tumor is localized under the nail plate, onycholysis or erythronychia is produced (Fig. 25.9). When multiple fibrokeratomas are present in fingernails and/or toenails, named Koenen tumors, they are one of the major criteria of tuberous sclerosis.

Fig. 25.9

(a) Fibrokeratoma under the nail plate with onycholysis. (b) Dermatoscopy (×10)

5 Alterations of the Nail Color

Alterations of the nail color can result from the deposition of a pigment on the nail plate or from the production of the pigment from the nail matrix. In the latter case, the color is within the nail plate.

5.1 Leukonychia

Children usually are affected by true leukonychia that is due to trauma to the distal matrix. In true leukonychia, the milky white discoloration is within the nail plate and results from the presence of foci of parakeratotic cells within the nail plate. The presence of nuclei impairs nail plate transparency and reflects light, resulting in the white color. Depending on the shape, leukonychia can be punctate or transverse. Punctate leukonychia is typical of several fingernails: onychoscopy shows a normally smooth nail plate surface and spots of white discoloration inside the nail plate (Fig. 25.10). Transverse leukonychia is quite rare in children and typically restricted to the first toenails. This variety of true leukonychia is due to trauma from the shoes to a thick nail plate, which transmits the trauma to the distal nail matrix, resulting in periodic defective keratinization with the production of one or more transverse white bands that move distally with nail growth [3]. The shape of the white spots inside the nail plate is in this case transverse.

Fig. 25.10

Punctate leukonychia in fingernails: dermatoscopy with gel (×10)

5.2 Splinter Hemorrhages

They are due to rupture of the blood capillaries of the nail bed and appear as longitudinal red to brown striae in the distal nail. Their shape reflects the shape of the capillaries of the nail bed, which run along the creases. Dermatoscopy allows an enhanced visualization of the splinter hemorrhages, which appear deep red in color and a few millimeters in length. Splinter hemorrhages may result from mechanical trauma or may be associated with other diseases, such as psoriasis (Fig. 25.11) or onychomycosis.

Fig. 25.11

Nail psoriasis. Dermatoscopy with gel (×20): multiple splinter hemorrhages

5.3 Subungual Hematoma

One of the best uses of onychoscopy is to distinguish blood from melanin [4]. Subungual blood extrusion due to trauma is very common in the toenails. Although the round shape of the hematoma is usually easy enough to distinguish it from a band of melanic nail pigmentation with the naked eye, the patient usually becomes aware of the presence of a brown-black nail pigmentation of one toenail that last for a long time. Dermatoscopy shows the round shape of hematoma, associated with a homogeneous color in the red-brown pigmentation, a globular pattern, a peripheral fading, and multiple blood globules or splinter hemorrhages around the hematoma. The color of hematoma depends on the time from the occurrence of the trauma. A recent hematoma is deep under the plate and red purple to black in color, with irregular margins but generally round at the proximal edge and with a streaked and filamentous distal end [5]. A new term is coined as pseudopods to refer to the distal end of a nail hemorrhage (Fig. 25.12) [6]. Older lesions are more superficial on the ventral nail plate and roundish, red brown in color, often surrounded by small globules of paler color or dots of coagulated blood with fading around the center of the lesion.

Fig. 25.12

Subungual hematoma. Dermatoscopy (×10): globular pattern and peripheral fading

5.4 Melanonychia

The term melanonychia refers to black-brown-gray pigmentation of the nail due to the presence of melanin within the nail plate. Usually it appears as a longitudinal band which starts from the proximal margin and extends to the distal margin of the nail following the growth of the nail. Onychoscopy can be useful for the evaluation and the management of melanonychia in a three-step process: (1) establish if the pigment is melanin or not; (2) determine if the pigmentation of melanin is due to an activation or proliferation; and (3) determine if the proliferation is benign or malignant [7].

Dermatoscopy is useful to differentiate melanotic from non-melanotic pigmentation, particularly the quite common nail brown-black discolorations due to subungual hematoma or fungal infection [8]. Generally, melanic pigmentation is brown black and within the nail plate, and the aspect is a longitudinal band, whereas exogenous pigmentation includes different types of color of the substance which adhere to the nail plate and not always have a longitudinal appearance. Onychoscopy of melanotic nail pigmentation is more difficult to interpret, as there are still not uniform criteria that allow us to differentiate melanonychia due to benign melanocytic proliferation, i.e., nail matrix lentigo or nevus, from melanonychia due to malignant melanocytic proliferation [7,8,9].

In case of melanonychia of multiple nails, a melanocytic activation, generally due to racial, systemic, or traumatic (nail biting) factors, should be suspected [9]. Dermatoscopy shows a gray background of the band with thin grayish regular and parallel lines (Fig. 25.13).

Fig. 25.13

Onychotillomania in a girl. Dermatoscopy (×10): longitudinal band due to melanocytic activation

Nail matrix nevi are typically seen in childhood and it may be congenital or acquired. Clinical and dermatoscopic parameters used in adults are not valid with children. The size and the degree of pigmentation of the band vary considerably; dark bands are associated with pseudo-Hutchinson’s sign, because the dark nail plate pigmentation is visible through the transparent nail fold [9,10,11]. Criterion suggesting biopsy in children is a rapid evolution of the band in growth and color. Dermatoscopic patterns that suggest a nevus are the presence of a brown background with longitudinal brown to black regular and parallel lines with regular spacing and thickness and, more important in children, black dots due to pigment accumulation in the nail plate (Figs. 25.14 and 25.15).

Fig. 25.14

Nail matrix nevus. (a) Longitudinal band of nail matrix nevus in a 2-year-old boy. (b) Dermatoscopy (×20)

Fig. 25.15

(a) Nail matrix nevus of the whole nail. (b) Dermatoscopy (×20)

Nail melanoma in children is rare and its frequency depends on the race and exceptional in Caucasians. Twelve cases are described in literature, frequently in pigmented races [12,13,14,15]. Dermatoscopic patterns that suggest a melanoma in children are brown background; lines from brown to black; irregular degree of color pigmentation, spacing, or varying thickness; ending abruptly of the distal nail plate; and a parallelism disruption of the bands (Fig. 25.16). However, these features can also be seen in longitudinal melanonychia in children, and their specificity in young age is very low.

Fig. 25.16

(a) Nail melanoma in an 18-year-old girl. (b) Dermatoscopy (×20)

5.5 Erythronychia

It is a red band originating from the proximal to the distal nail plate, due to the presence of a subungual mass at the level of the lunula. The corresponding nail plate is normal or sometimes has longitudinal fissures. When single, the band indicates the presence of a subungual tumor, such as onychopapilloma or glomus tumor. These tumors are rare in young children and affect mostly adolescent ages. Onychopapilloma occurs on the thumb, sometimes other digits, but rarely involves the toes. It appears as a longitudinal pink-red band often associated or composed entirely of splinter hemorrhages. With clipping the onycholysis of the distal nail plate, the free margin of the band is occupied by hyperkeratosis [15]. Onychoscopy reveals a well-defined longitudinal red band with splinter hemorrhages, starting from the lunula and reaching to the distal margin where it causes a fissure and a filiform hyperkeratotic mass (Fig. 25.17) [16].

Fig. 25.17

Onychopapilloma. Dermatoscopy (×10) showing erythronychia

When erythronychia affects multiple nails, they are usually due to an inflammatory disease such as nail lichen planus or Darier’s disease. Darier’s disease is an autosomal dominant genodermatosis characterized by a persistent eruption of hyperkeratotic greasy papules mainly over the seborrheic sites of the body, usually associated with nail abnormalities and sometimes with mucous membrane lesions. Onychoscopy shows alternating parallel longitudinal red streaks with thinning of the corresponding nail plate and white bands. The bed vessels are more visible and associated with splinter hemorrhages. Distal splitting of the nail plate may be more or less marked, especially along the red bands.

6 Abnormal Detachment

The abnormal detachment of the nail plate from the nail bed is known as onycholysis. Air passes underneath the nail plate and the color changes from pink to white. Other pigments can be deposited under the nail plate, coloring this space from yellow, such as in onychomycosis, or green due to pyocyanin, or red due to hemosiderin. Onycholysis is not specific, as it can be observed in traumatic, inflammatory, infective, or neoplastic disorders.

6.1 Traumatic Onycholysis

It can involve the fingernails, but is very common in the toenails. The detachment of the nail plate due to traumas frequently appears bilateral and symmetrical. At onychoscopy the line of detachment of the plate from the bed is linear, regular, and smooth and surrounded by a normally pale pink bed, without hyperkeratosis (Fig. 25.18) [17, 18]. The subungual space is usually whitish to yellow, and small black drops corresponding to splinter hemorrhages can be present.

Fig. 25.18

Traumatic onycholysis. Dermatoscopy (×20) of the linear proximal margin of the onycholytic area

6.2 Nail Psoriasis

Typical clinical signs of nail psoriasis in children are onycholysis, pitting, and subungual hyperkeratosis. Dermatoscopy allows the detection of subclinical signs that can be very helpful for a definitive diagnosis of nail psoriasis in doubtful cases. In onycholysis due to psoriasis, onychoscopy shows the presence of a bright orange-yellow border surrounding the distal edge of the detachment (Fig. 25.19), a slightly dented margin, and several splinter hemorrhages. Moreover, the salmon patches appear irregular in shape and size, with a color from red to orange [19, 20].

Fig. 25.19

Nail psoriasis. Dermatoscopy (×10) with a bright-orange-yellow border surrounding the distal edge of the detachment

6.3 Nail Lichen Planus

It is uncommon in children, and usually milder than in adults, with persistent nail damage rare [21,22,23]. Onychoscopy enhances visualization of the longitudinal fissures of the nail plate due to lichen planus. Dermatoscopic observation of the proximal nail plate allows the evaluation the disease’s course in a short time, since it shows the newly formed nail plate. Dorsal pterygium, rare in children, is the result of an irreversible damage to the nail matrix, with absent nail plate and adhesion of the dorsal skin to the nail bed, and formation of a v-shaped extension of the proximal nail fold (Fig. 25.20). Permanent anonychia is also rare.

Fig. 25.20

Toenail lichen planus. Dry dermatoscopy (×10): dorsal pterygium

6.4 Nail Lichen Striatus

It is rare and almost exclusively seen in children. Clinically, one nail is involved and shows lichenoid abnormalities with longitudinal ridging restricted to its medial or lateral portion that continues with skin lesions characterized by papules or verrucous scales along the Blaschko lines. Dry dermatoscopy permits to observe as longitudinal fissuring and distal splitting (Fig. 25.21).

Fig. 25.21

Nail lichen striatus of the first right thumb. Dermatoscopy (×10) of the nail plate

6.5 Onychomycosis

It is rare in children [24]. Toenails are more affected than fingernails. Predisposing factors include dermatophyte infection in other members of family, nail abnormalities, traumatic factors, and immunodepression. Although mycological examination is needed to confirm the diagnosis [24], onychoscopy can be utilized to differentiate onychomycosis from other diseases causing onycholysis, such as traumatic onycholysis or nail psoriasis, Moreover, dermatoscopy may be used as a guide to identify the best spot to obtain adequate samples for mycological examination [25].

In children dermatoscopy may be particularly useful in distal subungual onychomycosis (DSO) and white superficial onychomycosis (WSO) [26]. In DSO the fungi reach the nail unit through the hyponychium and invade the space under the nail plate progressing proximally. The dermatoscopic patterns of DSO are (Fig. 25.22) jagged edge of the proximal margin of the onycholytic area, with sharp structures (spikes) directed toward the proximal fold; white-yellow longitudinal striae in the onycholytic nail plate; an overall appearance of the affected nail plate in parallel bands of different colors, resembling aurora borealis and in fact named Aurora borealis pattern [18, 24]; and a “ruin appearance” of the subungual hyperkeratosis due to the accumulation of dermal debris of fungal invasion, better visible with frontal dermatoscopy [27]. In WSO the fungi colonize the dorsal surface of the nail plate with the production of small white spots on one or several nails [28]; dermatoscopy shows a nail plate with several small white opaque and friable patches (Fig. 25.23). For a better result of the image, performing dry dermatoscopy is recommended because the use of a gel for interface induces a partial disappearance of the white discoloration that includes the scales irregularly spread on the nail surface. In punctate leukonychia, in which dermatoscopy shows single or multiple opaque white regular spots within the nail plate, no change is visible after the application of the gel.

Fig. 25.22

Distal subungual onychomycosis. Dermatoscopy (×20): fringed proximal margin of the onycholytic area and spikes

Fig. 25.23

White superficial onychomycosis. Dermatoscopy (×20): small, white, opaque, and friable patch on the nail plate

7 Nail Tumors

Tumors in children are rare. The most frequent is represented by the subungual exostosis, a benign tumor of the bone of the distal phalanx occurring beneath the nails. Clinically it appears as a hard nodular lesion with a keratotic surface that elevates the nail plate, frequently in the great toenail. Usually, it affects children under 18 years of age who do sport with jumps because traumas increase the frequency. Dermatoscopy of the nail plate shows a white onycholysis of the distal part detached by the mass of the tumor. Frontal dermatoscopy is very helpful to better see the typical aspect of exostosis. It appears as a light red-colored nodule, pink or flesh-colored in color, which projects beyond the inner free edge of the nail (Figs. 25.24a, b). During the performing of the dermatoscopy, it is possible to notice the harness of the lesion on touching the lesion and the patient feels pain. The overlying nail can become brittle and may be lifted and the surface of the lesion may be hyperkeratotic. For this reason, it is better to use dermatoscopy with gel to observe nail plate onycholysis and dry dermatoscopy in the frontal view to better evidence the alteration of the surface of the lesion.

Fig. 25.24

(a) Subungual exostosis of the left toenail. (b) Frontal dermatoscopy (×40)