III.18.1 Definition
Nail nevus is a benign melanocytic tumor that involves any part of the nail apparatus [1–8].
Most cases involve the nail matrix, and rare cases involve the nail bed and/or the nail lateral folds. Extremely rarely a blue nevus, which cor- responds to a heavily pigmented, exclusively dermal melanocytic tumor, involves the nail ap- paratus.
III.18.2 Clinical Features
In most cases, the nail apparatus nevus involves the nail matrix and clinically produces a pig- mented longitudinal band on the nail plate. This band is the reflection of the melanin deposit in the nail plate during its early growth in the nail
Nail Apparatus Nevus (Subungual Nevus, Nail Matrix Nevus)
Luc Thomas
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Contents
III.18.1 Definition . . . .173
III.18.2 Clinical Features . . . .173
III.18.3 Dermoscopic Criteria . . . .173
III.18.4 Relevant Clinical Differential Diagnoses . . . .175
III.18.5 Histopathology . . . .175
III.18.6 Management . . . .176
III.18.7 Case Studies . . . .176
III.18.7.1 Case 1 . . . .176
III.18.7.2 Case 2 . . . .177
References . . . .180
matrix area and persists in the nail plate toward the distal edge. This clinical presentation is called the melanonychia striata syndrome. Mel- anonychia striata is also the clinical presenta- tion of early nail apparatus melanoma (see Chap. IV.11); therefore, this syndrome should be regarded cautiously and it is recommended to systematically consider this diagnosis regard- less of the other symptoms and regardless of the clinical context. Benign melanonychia striata, however, usually has its onset during childhood, is regular in its coloration, has parallel borders, and does not involve the periungual tissue. Het- erochromic melanonychia striata (especially in congenital nevi) and cases with involvement of the periungual tissue, the cuticle and supra-ma- tricial skin (also called Hutchinson’s sign; see Chap. IV.11), or the lateral folds can cause diag- nostic difficulties.
Blue nevus of the nail apparatus corresponds to a blue spot with a discoid distal edge and a proximal end often hidden from clinical exami- nation by the supra-matricial skin.
III.18.3 Dermoscopic Criteria
On the nails, immersion technique should be used for dermoscopy since polarized light ap- pears insufficient to properly illuminate the thick nail plate. We recommend to use gel im- mersion (uncolored ultrasound gel). In dermos- copy, in case of melanonychia striata syndrome, a nail apparatus nevus has a light- to dark-brown homogeneously colored background overlaid by regular longitudinal lines. These lines are regu- lar in their coloration, spacing, thickness, and do not show areas of parallelism disruption (Figs. III.18.1, III.18.2).
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Fig. III.18.1. Nail apparatus melanocytic nevus of the second right fingernail in a 26-year-old male skin-type-3b patient. Pigmentation has been present since childhood and the patient has observed no enlargement over the years. No other pigmented lesion of the toe and finger- nails has been found. The clinical picture corresponds to the classical melanonychia striata syndrome. The lesion is clinically monochromic, and no pigmentation of the peri-
ungual skin is observed. Dermoscopy shows a brown col- oration of the background overlaid by longitudinal lines regular in their color, spacing, thickness, and parallelism.
In such a case pathological confirmation of the diagnosis is usually not required; however, in this particular case a nail matrix biopsy was performed after the patient’s informed consent was obtained in the setting of a clinical study. It confirmed the diagnosis of junctional melanocytic nevus
Fig. III.18.2. Nail apparatus melanocytic nevus of the left thumbnail in an 8-year-old skin-type-4 male patient.
The lesion has been present since the age of 6 years and was stable in its dimensions and coloration since then.
Clinical picture corresponds to the classical melanonych- ia striata syndrome. By clinical observation we noticed that the lesion was monochromic and its borders were symmetrical. Note that there is a pseudo-Hutchinson’s
sign due to the visibility of the pigmentation through a translucent nail cuticle. This should not be confused with true Hutchinson’s sign, which corresponds to pigmented involvement of the periungual tissue. Dermoscopically, the lesion appears to be composed of regular longitudinal lines overlying a brown background. No biopsy was taken and the lesion remained stable after 4 years of clinical- dermoscopic follow-up
Nail apparatus blue nevi display the classical blue homogeneous pattern also observed on non-acral skin in dermoscopy; however, de- pending on their anatomic location, the proxi- mal edge is often hidden from the dermosco- pist.
III.18.4 Relevant Clinical Differential Diagnoses
The main differential diagnosis in the melano- nychia striata syndrome are the following:
1. Melanoma (see Chap. IV.11), acral lentiginous type, should always be considered in the differential diagnosis of a pigmented longitudinal band on the nail. Clinical criteria for malignancy are:
(a) onset during adulthood; (b) polychro- mic aspect; (c) pigmentation of the periungual tissue (Hutchinson’s sign); (d) enlargement of the band over time; and (e) broader band at the proximal end.
Dermoscopy shows an irregular pattern of the lines (irregular in width, color, spacing, and parallelism).
2. Lentigines are often polydactylic and are clinically associated with mucous membrane pigmentation in Laugier–
Hutzinger disease. Such lesions occur in adulthood. Dermoscopy reveals a
monochrome gray band with thin regular gray lines.
3. Ethnic pigmentation is observed in patients with skin types 5 and 6, the family history reveals similar pigmenta- tion in parents or siblings, and lesions occur in several finger- and toenails.
Dermoscopic features are similar to those observed in lentigines.
4. Drug-induced pigmentation is a very frequent phenomenon. Medical history reveals chronic exposure to a pigmento- genic medication (hydroxyurea, chlor- promazine, acyclovir, mynocyclin, etc.).
Lesions are polydactylic, and dermoscop- ic findings are similar to those of lentigi- nes.
5. Post-inflammatory reaction (toenail chronic friction with shoes, nail pigmen- tation after paronychia of any origin) is in most case polydactylic, and often
symmetric. Diagnosis is made by record- ing the patient’s history, observation of the topography of the involvement, and dermoscopic observation of changes similar to those observed in lentigines.
6. In some cases nail apparatus Bowen’s disease is pigmented; however, early periungual involvement and subungual hyperkeratosis is observed. These lesions occur during adulthood. Pathology determines the diagnosis.
In case of a blue pigmented spot, the differential diagnosis is subungual hemorrhage; however, these lesions are clinically characterized by their regressive evolution toward the distal edge of the nail plate as opposed to the clinical fixity of the blue nevi. Dermoscopy is extremely useful showing “blood spots” characterized by their round-shape proximal edge and their filamen- tous distal ending in case of subungual hemor- rhage.
III.18.5 Histopathology
Histopathological confirmation of the diagno- sis of subungual nevus is not mandatory in typ- ical cases; However, in case of doubt a nail ma- trix biopsy should be taken. This surgical procedure is difficult and often leaves a defini- tive longitudinal nail plate dystrophy. Moreover the “significant” tissue is very small and any in- appropriate management of the specimen could be misleading. Histopathology shows a melano- cytic hyperplasia at the basal layer of the matri- cial epithelium. No cell atypia is found and me- lanocytes do not exhibit prominent dendrites.
The dermal component is composed of nests of small round melanocytes regular in size and shape. Neither mitotic figures nor an inflam- matory infiltrate are found.
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III.18.6 Management
Treatment of nail apparatus melanocytic nevi is not mandatory. Abstention and follow-up are generally recommended because surgery is dif- ficult and painful and it leaves definitive scars on the nail plate. Treatment of lateral nail ap- paratus nevi is somewhat easier but scarRing process in the lateral nail fold often causes a lat- eral deviation of the nail plate. In case of surgi- cal treatment, complete excision of the nevus should be the goal because follow-up of a longi- tudinal nail pigmentation after partial surgery is extremely difficult since the scarring process causes irregular pigment distribution in the remnant lesion which is extremely difficult to differentiate from melanoma. The surgical exci- sion of a nevus of the nail matrix is conducted after incision of the submatricial skin. A suture of the nail matrix defect should be done with loose stitches. Even in experienced hands this surgery often leaves dystrophic changes of the nail plate. In our opinion, surgery should only be done in case of doubt.
III.18.7 Case Studies III.18.7.1 Case 1
Patient Comment
The lesion is observed on the right thumb of a right-handed 11-year-old skin-type-2 female patient. Her parents first noticed the lesion at the age of 4 years. Since then, the lesion has pro- gressively enlarged with the finger, but the pro- portion of the involved nail plate has remained the same. There is no complaint about this le- sion, and the small defect at the distal edge of the nail plate is due to a nail-clipping biopsy performed a few days prior to examination by another dermatologist (pathology found mela- nin in the nail plate). The parents referred their daughter to obtain a second opinion before po- tentially scarring surgery of the nail matrix.
Questions Asked By the Physician
The interview with the parents and child was quite precise about the age of onset. They pro- vided several family photographs in which the lesion was clearly identifiable. No esthetic com- plaint was formulated.
Clinical Image
Clinical observation disclosed a melanonychia striata syndrome without atypia. The coloration of the band was homogeneous, no Hutchinson’s sign is observed, and edges of the band were regular and parallel.
Dermoscopic Image
Dermoscopy showed a typical nevus pattern with regular parallel lines over a light brown background.
Clinical Diagnosis and Relevant Differential Diagnosis
The patient’s history as well as clinical and der- moscopic findings were highly suggestive of nail matrix melanocytic nevus. Melanoma should always be included in the differential diagnostic discussion of a monodactylic melanonychia striata syndrome; however, in this case the onset during childhood, the absence of band enlarge- ment over time, the regular clinical pattern of the band, and the nevus pattern on dermoscopy were sufficient enough to avoid unnecessary surgery on the thumb of the dominant hand of this young patient. Ethnic-type pigmentation is rarely monodactylic and never occurs in skin- type-2 patients.
Performed Management
The patient was included in a two-yearly follow- up program. No change has been observed.
Comments
Even though melanoma is rare in children, it should systematically be included in the differ- ential diagnosis of a melanonychia striata. In this case the patient’s medical history, clinical examination, and dermoscopy, as well as inclu- sion in a follow-up program, obviated the need for surgery.
III.18.7.2 Case 2
Patient Comment
This 26-year-old female skin-type-4 patient was referred for nail changes on her second right fin- ger. About 6 years prior to examination, she had noticed for the first time a blue pigmentation of the lunula. The lesion was then attributed to trauma and diagnosed as a subungual hemor- rhage; H=however, the pigmentation remained
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stable over time and showed no tendency toward regression or distal migration of the pigmenta- tion. An attempt of curettage of the nail plate surface did not permit to eliminate pigmenta- tion but left surface changes observed at the dis- tal part of the plate after nail outgrowth. The lesion was not painful, and X-ray of the distal phalanx was normal.
Questions Asked by the Physician
The patient’s interview clearly stated that the pigmentation did not enlarge over time and the absence of other symptoms. Examination of the other nails was normal as well as total skin ex- amination. The patient confirmed that changes observed on the distal nail plate were due to an unsuccessful attempt at superficial abrasion of
the plate by a previous examiner performed in order to rule out the diagnosis of subungual hemorrhage.
Clinical Image
If we except the artifactual changes of the distal plate, the clinical picture is limited to a hemi- circular blue discoloration of the lunula that is also observed through the cuticle (pseudo- Hutchinson’s sign). No periungual pigmenta- tion was seen.
Dermoscopic Image
The dermoscopic examination showed a homo- geneous blue pattern limited proximally by the
cuticle and with poorly defined distal limit. This image did not show “filamentous” distal aspect observed in subungual hemorrhages.
Clinical Diagnosis with Relevant Differential Diagnosis
The dermoscopic image was very similar to the blue homogeneous pattern observed in cutane- ous blue nevus. It was similar to the image pub- lished by Causeret et al [8]. Accordingly, our dermoscopic diagnosis was blue nevus. The main clinical and dermoscopic differential di- agnosis was subungual hemorrhage; however, the absence of distal migration over time and the fixity of the pigmentation despite the ab- sence of repetitive trauma and, moreover, the absence of “filamentous” pattern of the distal part of the pigmentation, were against this hy- pothesis. Subungual blue nevus is rare, however, and therefore pathological confirmation was preferred.
Management
Surgical exploration of the nail matrix area dis- closed a well-limited discoid blue pigmentation underneath the matricial tissue. Dissection of the submatricial tissue permitted the excision of a charcoal-black piece of dermis, At the end of the surgical procedure reposition of the nail matrix and of the supra-matricial tissue per- mitted a normal outgrow of an almost normal unpigmented nail plate within 5 months. Fol- low-up examination after 2 years showed no re- currence.
Histopathological Image
Histopathological examination of tissue re- moved during surgery showed an exclusively dermal proliferation of heavily pigmented cells.
Surgical margins were free. Cells were centered by well-nucleolated nucleus. Cytoplasm was filled by granulous or more homogeneous pig- ment deposits. Neither mitotic figures nor cell atypia were observed.
Histopathological Diagnosis and Clinicopathological Correlation
Diagnosis of ungual blue nevus (of the cellular subtype) was made. The complete confinement of the pigment deposit to the submatricial der- mal tissue explained the blue spot pattern ob- served on dermoscopy, and absence of involve- ment of the epithelial tissue explained the absence of longitudinal band.
Comments
Facing a well-circumscribed subungual blue pigmentation, clinical diagnosis vacillates be- tween subungual hemorrhage and blue nevus.
Clue for the diagnosis in favor of blue nevus are:
(a) the absence of distal migration of the pig- mentation with the outgrowing nail plate; and (b) the blue homogeneous pattern of the pig- mentation with semi-circular shaped distal end without “filamentous” distal pattern.
C Core Messages
■ Nail apparatus melanocytic nevus frequently occurs during childhood and its most common presentation is the melanonychia striata syndrome.
■ The main differential diagnosis is nail apparatus melanoma.
■ Dermoscopy shows a regular pattern of pigmentation.
■ In case of doubt surgical biopsy and histopathological examination are required.
■ In typical cases follow-up appears to be the most appropriate management since surgical therapy often leaves definitive nail dystrophy.
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References
1. Haneke E, Baran R (2001) Longitudinal melano- nychia. Dermatol Surg 27:580–584
2. Hirsch RJ, Weinberg JM (2001) Evaluation of pig- mented lesions of the nail unit. Cutis 67:409–411 3. Tosti A, Baran R, Piraccini BM, Cameli N, Fanti PA
(1996) Nail matrix nevi: a clinical and histopatholog- ic study of twenty-two patients. J Am Acad Dermatol 34:765–771
4. Goettmann-Bonvallot S, Andre J, Belaich S (1999) Longitudinal melanonychia in children: a clinical and histopathologic study of 40 cases. J Am Acad Dermatol 41:17–22
5. Ronger S, Touzet S, Ligeron C, Balme B, Viallard AM, Thomas L (2002) Dermoscopic examination of nail pigmentation. Arch Dermatol 138:1327–1333 6. Kawabata Y, Ohara K, Hino H, Tamaki K (2001) Two
kinds of Hutchinson’s sign, benign and malignant.
J Am Acad Dermatol 44:305–307
7. Johr RH, Izakovic J (2001) Dermatoscopy/ELM for the evaluation of nail apparatus pigmentation. Der- matol Surg 27:315–322
8. Causeret A, Skowron F, Viallard A, Balme B, Thomas L (2003) Subungual blue nevus. J Am Acad Dermatol 49:310–312
