Trichoscopy: Essentials for the dermatologist

Abstract

Noninvasive in vivo imaging techniques have become an important diagnostic aid for dermatology. Dermoscopy, also known as dermatoscopy, has been shown to increase the clinician’s diagnostic accuracy when evaluating cutaneous neoplasms. Dermoscope, both hand-held and videodermoscope, are nowadays a basic instrument for almost all the dermatologists around the world. Trichoscopy is the term coined for dermoscopic imaging of the scalp and hair. Routinely using dermoscopy and recognizing the structures and patterns of the different types of alopecia will likely improve the observer’s sensitivity for diagnosis and follow up of hair and scalp disorders. Structures which may be visualized by trichoscopy include hair shafts of different types, the number of hairs in one pilosebaceous unit, hair follicle openings (dots), the peri and interfollicular areas and the vasculature. This review summarizes the current knowledge about trichoscopic findings which may aid in the diagnosis of alopecia. Besides diagnosing alopecia, it has the potential for obviating unnecessary biopsies and when a biopsy is still needed it is helpful in choosing an ideal biopsy site. Moreover, trichoscopy can be a valuable tool for evaluating the treatment response photographically at each follow-up. Finally, we have discussed the utility of dermoscopy in inflammatory scalp disorders and infections.

Key Words: Alopecia; Dermatosis; Scalp; Dermoscopy; Dermatoscopy; Epiluminiscence microscopy; Diagnosis

Core tip: Trichoscopy refers to the dermoscopy of the hair and scalp disorders. This is a noninvasive, in office technique that can be performed with a hand-held dermatoscope or a digital videodermatoscopy system. Trichoscopy is useful for the diagnosis and follow-up of hair and scalp disorders. In this article, we have briefly described the most important trichoscopic patterns and structures.

INTRODUCTION

Non-invasive in vivo imaging techniques have become an important diagnostic aid for evaluating hair and scalp disorders. Trichoscopy is the term coined for dermoscopic imaging of the scalp and hair.

Trichoscopy is a simple and non-invasive technique that can be performed with both handheld dermatoscope and digital videodermatoscopy system[1]. The usual working magnifications with videodermatoscope are 20-fold to 70-fold. While the hand-held dermatoscope with 10-fold magnification may give easy and quick evaluation of hair, it does not precisely measure or document the observed findings[2].

The method allows quick identification of hair and shaft abnormalities without the need of hair sampling for ex vivo evaluation, i.e., optical or scanning electron microscopy. It is also a helpful tool in differential diagnosis of common acquired hair diseases, such as androgenic alopecia or diffuse alopecia areata[2].

TRICHOSCOPY STRUCTURES AND PATTERNS

Structures which may be visualized by trichoscopy include hair shafts, hair follicle openings, the perifollicular epidermis and the cutaneous microvessels.

Hair shafts

Trichoscopy allows analysing acquired and congenital hair shaft abnormalities.

Dermoscopy of the normal scalp shows regularly distributed follicular units, containing 1-4 hair shafts[1]. A normal terminal hair is uniform in thickness and color throughout its length. However, up to 10% of normal scalp hairs are vellus hairs that are lightly pigmented and measure < 3 mm in length and < 30 μm in thickness[1,3].

Trichoscopy also allows diagnosing most genetic hair shaft dystrophies such as monilethrix, trichorrhexis nodosa, trichorrhexis invaginata, pili torti or pili annulati[4] (Table 1).

Table 1 Hair shafts.

> 20% of vellus hairs	AGA, long lasting AA
Exclamation mark hairs	AA, trichotillomania, chemotherapy-induced alopecia
Pohl-Pinkus constrictions	AA, chemotherapy-induced alopecia, blood loss, malnutrition, chronic intoxication
Comma hairs	Tinea capitis
Corkscrew hairs	Tinea capitis
Coiled hairs	Trichotillomania
Flame hairs	Trichotillomania
Tulip hairs	Trichotillomania, AA
Regrowing pigtail hairs	AA, cicatricial alopecia
Zig-zag-shaped hairs	Tinea capitis

AGA: Androgenetic alopecia; AA: Alopecia areata.

Hair follicle openings: Dots

The term “dots” refers to the small, round hair follicle openings seen on trichoscopy. Trichoscopy may distinguish whether hair follicle openings are normal, empty, fibrotic or containing biological material, such as hyperkeratotic plugs or hair residues.

Black dots (cadaverized hairs) represent pigmented hairs broken or destroyed at scalp level.

Yellow dots are follicular infundibula with keratotic material and/or sebum. They vary in color, shape and size[4].

White dots may appear as fibrotic white dots or pinpoint white dots. The classic, big, irregular white dots represent areas of perifollicular fibrosis, observed in primary, folliculocentric cicatricial alopecias, and most commonly in lichen planopilaris[3]. The pinpoint white dots are small and regular, with occasional peripheral hyperpigmentation. They correspond to empty hair follicles or to the eccrine sweat ducts openings. They are observed in sun exposed areas and in dark skin phototypes.

Red dots have been described in discoid lupus erythematosus and in patients with vitiligo.

Pink-grey and grey dots have been observed in the eyebrow area of patients with frontal fibrosing alopecia[3]. This finding is believed to be a favourable prognostic factor for eyebrow regrowth (Table 2).

Table 2 Dots.

Black dots	Active AA, dissecting cellulitis, tinea capitis, chemotherapy-induced alopecia, trichotillomania, after laser depilation, after trichogram, incidental finding in other diseases
Yellow dots	AA: Marker of disease severity Discoid lupus erythematosus: Large, dark yellow to brownish-yellow dots Androgenic alopecia: "Oily" appearance and predominance in frontal area Dissecting cellulitis, trichotillomania: Imposed over dark dystrophic hairs
White dots	Primary folliculocentric alopecias, lichen planopilaris: Fibrotic white dots Dark skin, sun exposed areas: Pinpoint white dots
Red dots	Discoid lupus erythematosus, vitiligo
Pink-grey/grey dots	Frontal fibrosing alopecia (eyebrows)

AA: Alopecia areata.

Peri and interfollicular areas

The classification of peri- and interfollicular skin surface abnormalities in trichoscopy is based on features related to scaling, color, discharge and surface structure[3] (Table 3).

Table 3 Peri- and interfollicular areas.

Epidermal scaling	Diffuse scaling: Healthy individuals, psoriasis, seborrheic dermatitis Perifollicular scaling and tubular scaling structures: Lichen planopilaris, frontal fibrosing alopecia, folliculitis decalvans
Hyperpigmentation	Honeycomb: Sun exposed areas, dark skin phototypes Perifollicular: Androgenetic alopecia Scattered interfollicular: Discoid lupus erythematosus
Yellow or yellow-red discharge	Folliculitis decalvans, bacterial infections, dissecting cellulitis, tinea capitis
Structural changes in the skin surface	Starburst pattern hyperplasia in folliculitis decalvans

Blood vessels

Appearance of cutaneous microvessels in trichoscopy may vary in type and number depending on disease and activity of the process. Several inflammatory scalp disorders are characterized by a specific pattern of blood vessel arrangement on trichoscopy[3,4].

ALOPECIA

The interest for trichoscopy had greatly increased in the last years. There is an extensive literature on the different types of alopecia. Nowadays it has become an indispensable technique in the evaluation of the hair loss patient.

We have summarized the main trichoscopic findings in the most common types of non cicatricial (Table 4) (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5) and cicatricial alopecia (Table 5, Figure 6, Figure 7, Figure 8). In addition, there are some diagnostic algorithms in use for alopecia using trichoscopy (Figure 9).

Figure 1 Male androgenetic alopecia. Hair shaft thickness heterogeneity and predominance of follicular units with only one hair (Dermlite photo^®).

Figure 2 Female androgenetic alopecia. Significant (> 20%) diversity of hair shaft diameter. Note also yellow dots. Higher hair density and less variability in the occipital area (B) compared to the frontal area (A) (Dermlite photo^®).

Figure 3 Alopecia areata. Exclamation mark signs and black dots (Dermlite photo^®).

Table 4 Trichoscopic findings in common types of non cicatricial alopecia.

AGA	AA	Telogen effluvium	Trichotillomania
Hair shaft thickness heterogeneity	Exclamation mark hairs	Empty follicles	Simultaneous, chaotic coexistence of multiple hair shaft abnormalities
Increased proportion of vellus hairs	Broken hairs	Increased proportion of single-hair follicular units	Hairs broken at different lengths
> 10% thin hairs in the frontal area	Clustered short vellus hairs	Short regrowing hairs	Short hairs with trichoptilosis (split ends)
Increased proportion of single-hair follicular units	Pigtail hairs	< 20% hair diameter diversity	Coiled hairs
Yellow dots	Black dots	Brown perifollicular discoloration	Exclamation mark hairs
Perifollicular discoloration (peripilar sign)	Numerous yellow dots	No significant difference between frontal and occipital areas	Black dots
All the trichoscopic features appear most prominently in the frontal scalp area compared to the occipital area			Others: flame hairs, V-sign, hook hairs, hair powder and tulip hairs

AGA: Androgenetic alopecia; AA: Alopecia areata.

Figure 4 Telogen effluvium. Short regrowing hair (videodermoscopy, 70 x magnification). Photo courtesy of Prof. Lidia Rudnicka.

Table 5 Trichoscopic findings in common types of cicatricial alopecia.

LPP	FFA	DLE
Intense perifollicular scaling, tubular structures	Minor perifollicular scaling	Large yellow dots (follicular keratotic plugs)
Violaceous inter or perifollicular areas	Perifollicular erythema	Mottled dyschromia
Fibrotic white dots	Strong predominance of single-hair follicular units at the hair-bearing margin	Thin and radial arborizing vessels that emerge from yellow dots (“red spider in yellow dot”)
Blue grey dots	Absence of vellus hairs	Thick arborizing vessels at the perifery ot the lesion
Small hair tufts	Pink-grey and grey dots in the lateral eyebrow area	Follicular red dots

LPP: Lichen planopilaris; FFA: Frontal fibrosing alopecia; DLE: Discoid lupus erythematosus.

Figure 5 Trichotillomania. Hairs broken at differents lengths, with trichoptilosis (split end) and black dots (videodermoscopy, 70 × magnification). Photo courtesy of Prof. Lidia Rudnicka.

Figure 6 Lichen planopilaris. Intense perifollicular scaling and tubular structures (Dermlite Photo^®).

Figure 7 Frontal fibrosing alopecia. Absence of follicular openings, predominance of follicular units with only 1 hair, mild perifollicular scaling and perifollicular erythema (Dermlite photo^®).

Figure 8 Discoid lupus erythematosus. Characteristic large yellow dots and arborizing vessels (videodermoscopy, 70 x magnification). Photo courtesy of Prof. Lidia Rudnicka.

Figure 9 Diagnostic algorithm for trichoscopic findings of hair loss diseases. From Inui S. Expert Rev Dermatol 2012: 7.

ADVANTAGES AND LIMITATIONS OF TRICHOSCOPY

Standard methods used to diagnose hair disorders are clinical inspection, pattern of hair loss, pull test, trichogram, biopsy, chronology of preceding events, and screening blood test. They vary in sensitivity, reproducibility, and invasiveness. There is accumulated evidence that the use of trichoscopy in the clinical evaluation of hair disorders improves diagnostic capability beyond simple clinical inspection[5-7]. Trichoscopy have the advantages of being a quick and non-invasive, semiquantitative method. Trichoscopy allows to evaluate larger areas than other invasive techniques like biopsy or trichogram.

A recent study have demonstrated superiority of trichoscopy as compared to the trichogram, in the diagnosis of female androgenetic alopecia, especially in early cases[8].

An additional advantage of trichoscopy is that it allows digital surveillance and monitoring of the patients. Photographic evaluation at each visit is very appreciated by patients[9].

By the other hand, the use of trichoscopy can result in lower diagnostic accuracy if the physician does not recognize or correctly interpret the significance of structures. Moreover, trichoscopy can lead to lower diagnostic accuracy when patients are diagnosed using dermoscopy alone, without clinical context.

OTHER USES OF TRICHOSCOPY

Dermatoscopy in inflammatory scalp disorders and infections

Psoriasis and seborrheic dermatitis: Dermatoscopy of both cases shows diffuse or localized scales, which tend to be more yellowish in seborrheic dermatitis and more withish in psoriasis.

The major difference in this cases is the vascular pattern. Psoriasis shows red dots, globules and glomerular vessels. In seborrheic dermatitis the most common findings are arborizing and atypical red vessels and the absence of red dots and globules[1].

Pediculosis capitis: Trichoscopy is useful to observe the adult parasites ant to evaluate if the nits are empty or not.

Piedra and tinea capitis: Many features have been described in mycotic infections and dermatoscopy is very useful in these cases.

Trichoscopy guided biopsy

Trichoscopy may be used to select the best area from which to obtain a biopsy specimen[3].

Trichoscopy in general medicine

This includes possible application of trichoscopy in identifying follicular spicules in multiple myeloma, follicular mucinosis in lymphoproliferative disorders, scalp lesions in Langerhans histiocytosis or altered interfollicular microvessels in dermatomyositis and scleroderma[4].

Ex vivo dermatoscopy of scalp biopsies

Ex vivo assessment of scalp biopsies by dermatoscopy can identify the correct plane of transversal bisection and it is useful to control the tissue processing[10].

Trichogram using dermatoscopy

It has been proposed the use of dermoscopy when performing a trichogram, instead of using the optical microscope, as most of dermatologist nowadays have a dermoscope[1].