Consensus on melanonychia nail plate dermoscopy

Abstract

This statement, focused on melanonychia and nail plate dermoscopy, is intended to guide medical professionals working with melanonychia and to assist choosing appropriate management for melanonychia patients. The International Study Group on Melanonychia was founded in 2007 and currently has 30 members, including nail experts and dermatopathologists with special expertise in nails. The need for common definitions of nail plate dermoscopy was addressed during the Second Meeting of this Group held in February 2008. Prior to this meeting and to date (2010) there have been no evidence-based guidelines on the use of dermoscopy in the management of nail pigmentation.

This statement, focused on melanonychia and nail plate dermoscopy, is intended to guide medical professionals working with melanonychia and to assist choosing appropriate management for melanonychia patients.

The International Study Group on Melanonychia was founded in 2007 by Professor Antonella Tosti and Professor Nilton Di Chiacchio. The Group includes nail experts and dermatopathologists with expertise in nails from twelve different countries.

Prior to this meeting and to date there have been no evidence-based guidelines on the use of dermoscopy in the management of nail pigmentation.

16 members of the International Study Group on Melanonychia participated in this study.

A detailed literature search on nail dermoscopy, nail pigmentation and melanonychia including Medline, Embase, Cochrane and a hand search were carried out ^1-10 . Based on the available literature, the Group decided to develop an informal consensus process at S1 level.

The Group reviewed publications on melanonychia and nail plate dermoscopy (Pub med indexed or not), approved by the American Academy of Dermatology, Miami, 2010 (Table 1).

Table 1.

Review of the literature

First Author	Number of cases	Nail plate dermoscopy	Pathology
Imakado S, et al 6	2	Dermoscopic examination of the site of Hutchinson's sign showed irregular pigmentation on the ridge. Nail plate dermoscopy not described.	MM in situ
Gencoglan G, et al3	1	Homogeneous, brownish, regular bandlike pigmentations with indistinct borders were seen on 4 toenails	LHS
Antonovich DD, et al 7	1	With dermoscopy the pigmentation was observed as streaky and irregular.	MM in situ
Caseret AS, et al4	1	Homogeneous blue blotch and a regularly-pigmented grayish longitudinal melanonychia	Blue nevus
Iorizzo M, et al 8	2	C1: Dark brown to gray background with longitudinal and irregular parallel lines. Edges appeared ill-defined	MM in situ
		C2: No nail plate dermoscopy
Hirata SH, et al5	10	C1: Brown coloration of the background, brown-black regular lines	C1: TMH
		C2: Brown coloration of the background, regular lines	C2: TMH
		C3: Grayish and brown coloration of the background, regular lines	C3: TMH
		C4: Grayish and brown coloration of the background, regular lines	C4: TMH
		C5: Brown coloration of the background, brown-black regular lines	C5: JMN
		C6: Black coloration of the background	C6:TMH
		C7: Grayish and brown coloration of the background, regular lines	C7:CH
		C8: Grayish and brown coloration of the background, regular lines	C8:CH
		C9: Grayish and brown coloration of the background, regular lines	C9:CH
		C10: Brown coloration of the background, black regular lines	C10: OC
Hass N, et al 2	1	18 individual pseudopods protruded along its longitudinal axis, up to 1.1 mm in length and 0.2 mm wide and of straight or twisted shape	Hemorrhage
Kawabata Y, et al 11	24
		6 MM: Initially longitudinal pigmented streaks in the nail plate which increased in breadth, finally involving the whole nail plate, without deformities. Hutchinson's sign was observed in all cases.	6 MM
		18 BMN: 15 showed partial pigmentation in the nail plate, and in 3 the entire nail plate was involved, without deformities. Pigmented macu-les of the fingertip were observed in the same 3 cases and another 2 cases.	18 BMN
		However the surface profiles of the hyponychial pigmentation of subungual melanoma obtained by the dermoscope were different from those of BMN, although dermoscopic features of the nail plates are indistinguishable. The pattern of pigmentation of BMN had a brushy linear structure across the skin marks. In contrast, subungual melanoma in situ exhibited haphazard pigmentation distributed in a disorderly fashion over the entire surface.
Ronger S, et al 1	148	Melanoma (20 cases): association of brown pigmentation of the background (19/20; 95%) with longitudinal brown to black lines irregular in their coloration, spacing, thickness and parallelism. The irregular pattern of the lines was significantly associated with melanoma when compared with all other diagnoses (P=.001, taken either individually or as a group (P=.001 in all 5 differential diagnoses). Melanoma shared with melanocytic nevus the brown coloration of the background.	20 MM
		Melanocytic nevus (37 cases): brown background (37/37; 100%) and the regular pattern of the longitudinal lines (35/37; 95%) . The presence of these lines, regular in their thickness, spacing, coloration, and parallelism, was found statistically sufficient to distinguish nevus from melanoma (P=.001).	37BMN
		Drug-induced nail pigmentation (16cases): grayish coloration of the background (15/16; 94%) and the presence of thin longitudinal gray lines with regular thickness, spacing, coloration and absence of parallelism disruption. These dermoscopic findings were no different from the ones observed in ungual lentigo or ethnic-type pigmentation, but significantly differed from melanoma (P=.001).	16 DHNP
		Nail apparatus lentigo (45 cases): grayish coloration of the background (44/45; 98%) and the presence of thin longitudinal gray lines, regular in their coloration, thickness and spacing (42/45; 93%). The presence of these 2 criteria significantly differentiated nail lentigo from melanoma (P=.001).	45 NAP
		Ethnic-type pigmentation (8 cases): The patterns in these cases were similar to those previously described in ungual lentigo and drug induced nail pigmentation, but significantly different from those of melanoma (P=.001). The two characteristic dermoscopic features of ethnic-type nail pigmentation were the grayish background (7/8; 87.5%) and the thin, regular gray lines (7/8; 87.5%).	8ETP
		Subungual hemorrhage (22 cases): well-defined, rounded proximal edge and a purple to brown coloration were observed in all cases of subungual hemorrhages (22/22; 100%).	22 SH
Bilemjian APJ, et al 10	2	C1: 1st right digit : Lateral side: A light and dark brown color pigmentation, distributed in a linear and parallel fashion throughout the nail from the cuticle to the free edge.	C1: MM in situ
		Medial part: A totally amorphous and irregular area, affecting the proximal nail fold - the micro-Huntchinson sign.
		C2: 5th left digit: Brown parallel homogeneous longitudinal lines; regular in space, width and color.	C2: TMH

LHS: Laugier Hunziker Syndrome

OC: Onychomycosis

ETP:Ethnic type pigmentation

TMH: Typical melanocytic hyperplasia

BMN: Benign melanocytic nevi

SH: Subungual hemorrhage

JMN: Junctional melanocytic nevus

DHNP: Drug-induced nail pigmentation

MM: Malignant Melanoma

CH: Constitutional pigmentation (Hypermelanosis)

NAL: Nail apparatus lentigo

This clinical consensus statement proposes consideration of a number of important points. About the technique used for nail dermoscopy, devices, polarized and non- polarized that can be used for nail plate dermoscopy. No evidence or consensus exists on which instrument and what kind of light source is the most effective. The color and definition of the lines may vary among the different devices. The group suggests using the same device in the follow-up evaluation of the patient, with magnification of 10X (the best). This allows the whole nail plate to be seen in the field, as well as the regularity of lines to be evaluated. The best immersion fluid for the nail plate is ultrasound gel.

According to the patterns found, the group agrees that nail plate dermoscopy is useful to distinguish blood from melanin. Subungual hemorrhages have a distinct pattern of globules, with or without distal streaks, with a range of color varying from red to brown to black (Figure 1A). The risk of coincidental bleeding from a subungual tumor must be taken into consideration. The dermoscopic diagnosis of subungual hematoma does not rule out a coincident nail tumor.

FIGURE 1.

A - Subungual hemorrhages showing pattern of globules: B - Benign melanonychia due to melanocyte activation - difficult to distinguish a light brown from a gray background: C - Benign lesions in children (nevus) showing a brown background with longitudinal lines of different color and width: D – A melanoma with dark background with areas of different hue of pigmentation

According to the literature, the pattern of benign melanonychia due to melanocyte activation (ethnic-type or drug-induced pigmentation) and lentigo exhibits a homogeneous gray coloration of the background with thin longitudinal gray lines. The group agrees that it is difficult to distinguish a light brown from a gray background and that a gray background is infrequently observed (Figure 1 B). The color of the background is not a distinctive feature of benign lesions due to melanocyte activation. The color due to the melanin deposition may vary depending on the thickness of the nail and melanin location within the nail plate because of the "Tyndall" effect.

The brown background associated with regular parallel lines of identical color, spacing, and width suggests a benign lesion, either nevus or lentigo. The group agrees, even though this regular pattern is not often observed. Most benign lesions in children and adults show a brown background with longitudinal lines of different color and width. Line distribution within the band is most frequently irregular (Figure 1 C).

The brown background associated with longitudinal lines that are irregular in color, width, spacing, and parallelism is suggestive of malignant melanoma. The group agrees that benign nevi in children often show this pattern. Even in benign lesions of adults, individual lines may be irregular in width and color. The important point is the homogeneity of color and width of each individual longitudinal line. If an individual line shows irregularity in color or width along its length this is considered suspicious of melanoma. Melanoma in adults often shows a diffuse dark background with barely visible lines (Figure 1 D). The group agrees that a dark background with areas of different hue of pigmentation is suggestive of melanoma even in the absence of irregular lines.

Other applications of dermoscopy at the nail apparatus are reported. Distal edge dermoscopy is helpful for identifying the origin of the pigment producing lesion (distal or proximal matrix). The group agrees that distal edge dermoscopy is not always useful, particularly when the nail plate is thin. The same applies to very dark or very light bands. Dermoscopy of the hyponychium allows to distinguish pigmentation due to melanocytic nevi characterized by linear pigmentation in the furrows or across the skin marks, from pigmentation associated with nail melanoma (Hutchinson's sign), where dermoscopy shows haphazard pigmentation distributed in a parallel ridge pattern in a disorderly fashion.¹¹ The group agrees that dermoscopy of the hyponychium is useful in cases where melanonychia is associated with pigmentation of the hyponychium.

The group agrees that the nail plate dermoscopic patterns stated in the literature, as indicative of nail melanoma, need to be modified as follows:

• Brown bands with lines irregular in color, width and spacing are not indicative of melanoma in children;

• Benign lesions in adults can present with irregular lines and spacing; and

• Melanoma in adults is often present with a very dark background where the lines are difficult to see.

The group also agrees that at present any decision to excise should be based on established clinical criteria (history and physical exam) and not on nail plate dermoscopy patterns. Dermoscopy of the hyponychium is very useful for differential diagnosis between nevi and melanoma in the case of pigmentation of the periungual tissues.