A Compendium of Common Signs in Dermoscopy, Trichoscopy, and Onychoscopy

Abstract

Epiluminescence microscopy, also known as dermoscopy (or dermatoscopy), is a noninvasive tool which helps in identifying features which may not be visible to the unaided eye. Dermoscopic signs in dermatology, trichology, and onychology are evolving concepts for ease in diagnosis of certain dermatological disorders. Although all these signs have been published in different articles and texts as a scattered information, this article intends to consolidate the pertinent signs and create an easy reference for dermatologists in order to establish prompt diagnosis during their busy schedules.

Introduction

Dermoscopy is continually gaining appreciation in the field of clinical dermatology, by aiding in diagnosis of scalp/hair diseases (trichoscopy), nail/nail fold abnormalities (onychoscopy), inflammatory dermatoses (inflammoscopy), cutaneous infections or infestations (entomodermoscopy), and mucoscopy (mucosal surface).[^1,2] Recent data indicate that it might also be profitable in assessing the outcome and adverse effects of various treatments. The subtle signs in dermoscopy have become almost pathognomonic for certain diseases. There is, however, a learning curve to grasp these signs while examining the patient.

Signs in Dermoscopy

1. Jelly sign: Lesions of epidermal melasma show diffuse reticular pigmentation in different shades of brown with sparing of the follicular and sweat gland openings, hence forming a pseudo network pattern with concave borders.[³] This sign has also been described in seborrheic keratosis and solar lentigines where the pigment on the surface of the skin can appear to be like “jelly spread over the skin”[^4,5]
2. Wobble sign: The wobble sign technique may aid in differentiating a seborrheic keratosis from a compound nevus. To perform this technique, place the glass plate of the dermatoscope over the lesion, apply horizontal pressure to the lesion, and gently move it horizontally from side to side (parallel to the skin surface). A seborrheic keratosis remains more fixed to the surface of the skin and does not wobble (negative wobble sign) whereas a compound nevus is more pliable or rubbery and will easily move from side to side (positive wobble sign)[^6,7]
3. Rosette sign: Seen in actinic keratosis (nonpigmented) and thin squamous cell carcinoma. It is seen in polarized light only and consists of a white four-leaf clover-shaped structure [Figure 1]. This reflects the optical effect of polarized light interacting with follicular openings containing orthokeratosis and parakeratosis. This sign is seen less commonly in actinically damaged skin, basal cell carcinoma, and melanoma and has been recently reported in discoid lupus erythematosus[^8,9]
4. Isobar sign: Lentigo maligna (LM) and pigmented actinic keratosis (pAK) can be differentiated dermoscopically by the presence of a prominent pseudo network located between keratin-filled ostial openings in the latter, which is rarely seen in LM. Additionally, dermoscopy of LM may show a darker dot within the ostial openings, known as the isobar sign. This sign is rarely seen in pAK[¹⁰]
5. Rainbow sign: This sign (or pattern) is seen in pyogenic granulomas and Kaposi’s sarcoma. It is visible only when viewed with a polarized light dermatoscope, and as the name denotes, it refers to the kaleidoscope of colors resembling a rainbow seen within the lesion[¹¹]
6. Beauty and the beast sign: An acquired melanocytic nevi (denoted as “beauty”) will have a symmetry of pattern, color, and structure, whereas a melanoma (“beast”) will show some degree of asymmetry of pattern, color, and structure, hence not look pleasing to the viewer. Characteristic features of a melanoma will be atypical and negative pigment network, atypical dots and globules, streaks, off-center blotches, blue-white veil, regression structures, and/or ominous vascular structures[¹²]
7. Ugly duckling sign: Most individuals have a predominant nevus pattern among all other nevi, hence most nevi resemble each other just like siblings. An atypical nevus which does not follow the predominant nevus pattern may represent a dysplastic nevus or melanoma dysplastic nevus[^13,14]
8. Little red riding hood sign: In fair-skinned and light-colored hair individuals, visualizing or diagnosing amelanotic melanomas may be difficult with the naked eye. In such patients, dermoscopy is a valuable tool[¹⁵]
9. Collarette sign: Seen in pityriasis rosea wherein white scales are seen at the periphery of the lesion (collarette), in a structureless yellowish background [Figure 2]. Dotted vessels are seen as well, which, unlike psoriasis, are dispersed in an irregular or focal pattern[¹⁶]
10. Biett’s sign: Presence of a collarette of scales surrounding the hyperpigmented macules or papules on the palms and soles is called as the Biett’s sign, and it is considered to be a strong indicator of secondary syphilis. Dermoscopy is useful in visualizing the mild scaling which may not be appreciated by an unaided eye[¹⁷]
11. Neighborhood sign: The presence of multiple similar-looking lesions (neighbors) is an important clinical clue to differentiate actinic keratosis (which has a positive neighbor sign) from LM of the face, nose, and ears[⁵]
12. Pearl necklace sign: Described in the dermoscopy of clear cell acanthoma wherein glomerular and punctiform vessels can be seen in a “pearl necklace” distribution, an image highly characteristic of clear cell acanthoma[¹⁸]
13. Hang glider sign: Dermoscopy of nodular scabies usually shows dotted vessels, along with the presence of mites (“hang glider sign”) in some cases[¹]
14. Auspitz sign: In psoriasis, vascular structures may be poorly visible and removal of the scale or the use of a fluid interface may improve their visualization, on doing so, red dots or tiny red blood drops can be visualized [Figure 3]. This is called as the Auspitz sign[¹⁹]
15. Yellow clod sign: In acute exudative dermatitis, dotted vessels are seen in a patchy distribution and yellowish-brown to dark brown-colored serocrusts predominate (yellow clod sign), whereas in chronic and lichenified lesions, predominantly dotted vessels in a patchy distribution and scaling are seen[¹]
16. Anal groove sign: Using polarized dermatoscope, the anal groove appears as a crescent-shaped depression over the ventral surface of the Ixodes tick which wraps anteriorly around the anus [Figure 4]. In other ticks, the anal groove wraps posteriorly around the anus. Hence, dermoscopy can be a useful bedside test for diagnosing Lyme’s disease (Ixodes tick is the vector for Lyme’s disease)[²⁰]
17. Double-edge sign: First described by Yang et al., double-edge sign is seen in Bowen’s disease and appears as two parallel pigmented lines surrounding the lesion. Histopathologically, it corresponds to acanthosis in the center and two strips of hyperpigmented basal keratinocytes in the periphery.[²¹]

Figure 1: (a) Polarized dermoscopic image showing the white rosette sign (blue arrow). (Picture courtesy Dr. Siddharth Mani), (b) an ex vivo image of basal cell carcinoma with numerous rosettes (blue square) (Image taken with permission from “Rosettes and other white shiny structures in polarized dermoscopy: histological correlate and optical explanation” by M. Haspeslagh et al. [JEADV. DOI: 10.1111/jdv. 13080])

Figure 2: Dermoscopy showing a peripheral collarette of white scales in a lesion of pityriasis rosea – ”collarette sign”

Figure 3: Dermoscopic Auspitz sign in psoriasis, showing tiny spots of hemorrhage appreciable on dermoscopy (blue circles)

Figure 4: Polarized dermoscopic image showing the anal groove wrap anteriorly around the anus of an Ixodes tick (see arrow). The inset shows magnification of the anal groove (Image taken with permission from Connolly, D. M., and Lee, J. B. (2017). The anal groove sign: The use of dermatoscopy for identification of Ixodes ticks. Journal of the American Academy of Dermatology, 76, S64–S65)

SIGNS IN TRICHOSCOPY

1. Peripilar sign (perifollicular halo): A brown peripilar halo seen around the perifollicular ostium, suggestive of perifollicular inflammation, is seen in early androgenetic alopecia (AGA) and female pattern hair loss (FPHL).[²²] White peripilar halo is a sign of advanced stages of AGA and is considered to be due to atrophy of the hair follicles.[²²] This can be a poor prognostic finding in regard to therapy. Extensive peripilar sign is a poor prognostic factor for AGA and FPHL.[²³] Extensive peripilar sign is also seen in anagen effluvium and is postulated to be due to the effect of ultraviolet rays, chemical exposure, and melanocytes[²³]
2. Regularly bended ribbon sign, also known as regularly twisted ribbon sign: Seen as a feature of monilethrix on trichoscopy, it is characterized by uniform elliptical nodes and intermittent constrictions. The hairs are regularly bent at many locations and have a tendency to fracture at the sites of constrictions[^24,25]
3. Coudability sign: This is the characteristic feature of alopecia areata, and is much appreciated by trichoscopy [Figure 5]. On manually pushing the tapered hairs inward toward the scalp, the proximal hair shaft tends to bend or kink, at the site where the hairs shaft and narrow[²⁶]
4. V sign: Seen in trichotillomania (TTM) and traction alopecia [Figure 6]. When two hairs of a follicular unit are broken at the same time, it is seen as the letter “V.” It should be differentiated from the “V sign” seen after regrowth of shaving hairs. In TTM, surrounding hairs are of normal length whereas “V sign” is present in all the shaving hairs[²⁷]
5. Mace sign: This is a recently described entity in trichoscopy of active TTM for broken terminal hairs which are uniform in diameter, slightly darker than the surrounding hair, and with a bulging distal end [Figure 7]. The bulging distal end looks akin to the head of a mace whereas the proximal end resembles the handle of the mace. Mace sign has been considered the most specific diagnostic feature of TTM according to Malakar et al. Due to constant manipulation of the hair by the patient, there occurs splaying of the end of the hair giving the appearance of a bulge[²⁸]
6. Burnt matchstick sign: A burnt matchstick appearance is described as darker looking bulbar proximal tip followed by a linear stem of variable length [Figure 7]. This can be attributed to constant pulling and traction of hair as seen in TTM[²⁹]
7. Starburst sign: Trichoscopy of an active lesion of folliculitis decalvans will show tufted hairs surrounded by perifollicular hyperplasia, which may be arranged in a starburst pattern (starburst sign)[³⁰]
8. Fried egg appearance/sign: A trichoscopic finding, showing the presence of large yellow dots with a whitish halo. These are considered to be empty hair follicles surrounded by an acanthotic outer root sheath (ORS). It is specific for scalp lesions of pemphigus (more often in pemphigus vulgaris as compared to pemphigus foliaceus). In pemphigus foliaceus, an inverse version of this sign (white dots with yellow halo) has been seen[³¹]
9. Nikolsky’s sign of the hair: Acantholysis of the ORS keratinocytes in pemphigus vulgaris may lead to formation of hair casts. As the hair grows, part of the ORS keratinocytes is carried up through the follicular ostia to form a cylindrical structure enveloping the shaft: the hair cast. It denotes subclinical involvement of the hair follicle[³²]
10. Toothbrush sign: In folliculitis decalvans (also known as tufted folliculitis), multiple hairs (7 to 100 in number) in the form of tufts and surrounded by a peripilar cast, are seen coming out from a single follicular opening. Presence of more than 7 hairs emerging together from the follicular opening is considered diagnostic[³³]
11. Halo sign: This sign has been recently proposed by Agarwal et al. Black dots are seen in alopecia areata, tinea capitis, and TTM. On trichoscopy, a complete or arcuate grayish-white halo can be seen around the black dots [Figure 7], which is due to the proximal submerged part of the hair shaft that refracts polarized light through the epidermis, this was proposed as the halo sign[³⁴]
12. Wipeout sign: This sign has been recently proposed by Agarwal et al. Black dots seen in alopecia areata, tinea capitis, and TTM can be easily mistaken with hair dust (powder), which is specific to TTM. Unlike black dots, hair dust, which occurs due to complete disintegration of the decapitated hair, can be easily removed with a cotton bud, hence this sign was proposed as the “wipeout sign.[³⁴]
13. Eastern pancake sign: Trichoscopy of alopecic and aseptic nodules of the scalp shows the presence of nonuniformly arranged dilated follicular orifices without any features of alopecia areata, this was termed as Eastern pancake sign by Bourezane et al.[³⁵]
14. Handlebar sign: Seen in pseudofolliculitis of the beard region, wherein dermoscopy shows presence of curved hair attached to the skin on either side [Figure 8].[³⁶]

Figure 5: Coudability sign seen on dermoscopy (within blue circle)

Figure 6: The “V” sign (within the blue circle), appreciable on dermoscopy of trichotillomania

Figure 7: Various dermoscopic features of trichotillomania: burnt matchstick sign (green circle), flame hair (orange circle), mace sign (yellow circle), and black dot with halo sign (blue circle)

Figure 8: A dermoscopic image of pseudofolliculitis, showing the handlebar sign (blue circles)

SIGNS IN ONYCHOSCOPY

1. Hutchinson’s and pseudo-Hutchinson’s sign: In melanoma involving the nail matrix, an irregular band comprising multiple longitudinal brown-to-black lines with irregular spacing is seen on dermoscopy. A pigmentation of the nail fold cuticle and the surrounding periungual skin (proximal or lateral nail fold) can be observed frequently.[³⁷] In pseudo-Hutchinson’s sign ,the nail matrix pigmentation is seen through a translucent cuticle. This is very common in nevi (junctional more than compound nevi) and occurs more often in fingernails than toe nails [Figure 9]. Table 1 enlists the causes of pseudo-Hutchinson’s sign[^37,38]
2. Micro-Hutchinson sign: Pigmentation of the cuticle that can only be seen clearly with the help of a dermatoscope. It is observed in melanoma and rarely in nevi.[³⁹]

Figure 9: A dermoscopic image of the pseudo-Hutchinson’s sign, wherein the nail matrix pigmentation can be visualized through a translucent cuticle (Picture courtesy Dr. Siddharth Mani)

Table 1: Conditions associated with pseudo-Hutchinson’s sign

Conclusion

Understanding the above-highlighted signs in dermoscopy, trichoscopy and onychoscopy would make it convenient to diagnose certain conditions as a bedside procedure using a dermatoscope, hence precluding unnecessary invasive diagnostic methods such as biopsy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Acknowledgements

We acknowledge our family for their support. We thank Dr. Si ddharth Mani for providing some of the images.