Trichoscopy (or dermoscopy of hair and scalp) is an easy in-office technique that may be performed with a handheld dermoscope or a digital videodermoscopy system. This method is gaining increasing popularity, because it may be applied in differential diagnosis of multiple hair and scalp diseases. The focus of this article is application of trichoscopy in differential diagnosis of the most frequent hair and scalp diseases in dermatologic practice. Trichoscopy of genetic hair shaft abnormalities are briefly addressed. A new classification of perifollicular and interfollicular skin surface abnormalities is proposed.
Key Points
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Trichoscopy (hair and scalp dermoscopy) may be performed with any handheld or digital dermoscope.
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This method may be used as a diagnostic aid in differential diagnosis of hair loss and scalp diseases and in monitoring therapy.
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Trichoscopy diagnosis is based on evaluation of hair shafts, follicular openings, and perifollicular epidermis.
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Characteristic trichoscopy features of several hair and scalp diseases are known. These diseases include alopecia areata, androgenetic alopecia, discoid lupus erythematosus, folliculitis decalvans, genetic hair shaft abnormalities, lichen planopilaris, scalp psoriasis, tinea capitis, and trichotillomania.
Trichoscopy (or dermoscopy of hair and scalp) is an easy in-office technique that may be performed with a handheld dermoscope or a digital videodermoscopy system. This method is gaining increasing popularity, because it may be widely applied in differential diagnosis of hair and scalp diseases.
Trichoscopy is based on analysis of structures that may be visualized with a dermoscope. These basic structures may be divided into 4 groups: (1) hair shafts, (2) hair follicle openings (dots), (3) perifollicular epidermis, and (4) blood vessels.
Basic structures
Evaluation of Hair Shafts
The authors have recently suggested a classification of hair shaft abnormalities that may be visualized by trichoscopy. This classification distinguishes the following groups of hair shaft abnormalities: (1) hair shafts with fractures, (2) hair narrowings, (3) hairs with node-like structures, (4) curls and twists, (5) bands, and (4) short hairs. Only selected types of abnormalities are discussed in this article.
Many types of short hairs appear crucial for differential diagnosis of the most frequent types of hair loss in clinical practice. These are hairs that are less than 5 mm long. They include, among others, bent and hypopigmented vellus hairs, which are most characteristic of androgenetic alopecia. Vellus hairs may be also present in long-lasting, severe alopecia areata. Another type of short hairs is comma and corckscrew hairs, which are characteristic for tinea capitis. Short flame-like hairs are observed in trichotillomania.
Micro–exclamation mark hairs are hairs with narrowings at the proximal end. This type of abnormality is observed in alopecia areata and in trichotillomania.
Evaluation of Hair Follicle Openings (Dots)
With trichoscopy, whether hair follicle openings are normal, empty, fibrotic, or contain biologic material, such as hyperkeratotic plugs or hair residues, may be distinguished. Dots is a common term for hair follicle openings seen by trichoscopy.
Black dots (formerly called cadaverized hairs) represent pigmented hairs broken or destroyed at scalp level. They are observed in alopecia areata, dissecting cellulitis, tinea capitis, and trichotillomania.
Yellow dots are hair follicle openings that contain keratosebaceous material. They may be observed in alopecia areata, discoid lupus ertythematosus, and female androgenic alopecia. Rarely, yellow dots may be observed in telogen effluvium and trichotillomania. Yellow dots, appearing as large 3-D soap bubbles imposed over dark dystrophic hairs, are specific for dissecting cellulitis.
There are 2 types of white dots: classic, big, irregular white dots and pinpoint white dots. Classic white dots represent areas of perifollicular fibrosis and are observed most commonly in lichen planopilaris. Pinpoint white dots correspond to hair follicle openings and eccrine gland openings, observed within pigmented background. They are present in patients with dark skin phototypes, regardless of hair loss.
Red dots are described in discoid lupus erythematosus and are considered a good prognostic finding, indicating possible hair regrowth.
Regularly distributed gray or brown-gray dots are a characteristic finding in the eyebrow area of patients with frontal fibrosing alopecia.
Evaluation of Perifollicular Epidermis
Abnormalities of scalp skin color or structure that may be visualized by trichoscopy include scaling, changes in color, abnormalities in skin surface structure, and presence of discharge. A new classification of these abnormalities is presented in Box 1 , which indicates the clinical significance of individual abnormalities.
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Scaling
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Diffuse
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White (psoriasis, discoid lupus erythematosus, allergic dermatitis, dry skin)
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Yellowish (seborrheic dermatitis, discoid lupus erythematosus, ichthyosis)
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Perifollicular
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Color of scales
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White (lichen planopilaris)
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Yellowish (folliculitis decalvans)
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Shape of scale arrangement
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Tubular (lichen planopilaris)
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Tubular with collar formation (folliculitis decalvans)
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Color
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Brown areas
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Honeycomb hyperpigmentation (common)
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Perifollicular; peripilar sign (female and male androgenetic alopecia, telogen effluvium, healthy individuals)
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Scattered (discoid lupus erythematosus, actinic keratosis)
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White areas (cicatricial alopecia, detached epidermis, edema)
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Pink, strawberry ice cream–color areas (early fibrosis in cicatricial alopecia)
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Yellow areas (dissecting cellulitis, follicular pustules, bacterial infection)
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Red (inflammation, extravasation, erosion, vascular abnormalities)
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Violaceous blue (lichen planopilaris, discoid lupus erythematosus)
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Discharge
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Yellow and yellow-red (folliculitis decalvans, bacterial infections, dissecting cellulitis, tinea capitis)
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White follicular spicules (monoclonal gammopathy)
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Surface structure
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Starburst pattern hyperplasia (folliculitis decalvans)
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Evaluation of Blood Vessels
Appearance of cutaneous microvessels in trichoscopy may vary in type, arrangement, and number, depending on disease. Analysis of blood vessel arrangement is of special importance in differential diagnosis of inflammatory scalp diseases, such as scalp psoriasis, seborrheic dermatitis, or discoid lupus erythematosus.
Basic structures
Evaluation of Hair Shafts
The authors have recently suggested a classification of hair shaft abnormalities that may be visualized by trichoscopy. This classification distinguishes the following groups of hair shaft abnormalities: (1) hair shafts with fractures, (2) hair narrowings, (3) hairs with node-like structures, (4) curls and twists, (5) bands, and (4) short hairs. Only selected types of abnormalities are discussed in this article.
Many types of short hairs appear crucial for differential diagnosis of the most frequent types of hair loss in clinical practice. These are hairs that are less than 5 mm long. They include, among others, bent and hypopigmented vellus hairs, which are most characteristic of androgenetic alopecia. Vellus hairs may be also present in long-lasting, severe alopecia areata. Another type of short hairs is comma and corckscrew hairs, which are characteristic for tinea capitis. Short flame-like hairs are observed in trichotillomania.
Micro–exclamation mark hairs are hairs with narrowings at the proximal end. This type of abnormality is observed in alopecia areata and in trichotillomania.
Evaluation of Hair Follicle Openings (Dots)
With trichoscopy, whether hair follicle openings are normal, empty, fibrotic, or contain biologic material, such as hyperkeratotic plugs or hair residues, may be distinguished. Dots is a common term for hair follicle openings seen by trichoscopy.
Black dots (formerly called cadaverized hairs) represent pigmented hairs broken or destroyed at scalp level. They are observed in alopecia areata, dissecting cellulitis, tinea capitis, and trichotillomania.
Yellow dots are hair follicle openings that contain keratosebaceous material. They may be observed in alopecia areata, discoid lupus ertythematosus, and female androgenic alopecia. Rarely, yellow dots may be observed in telogen effluvium and trichotillomania. Yellow dots, appearing as large 3-D soap bubbles imposed over dark dystrophic hairs, are specific for dissecting cellulitis.
There are 2 types of white dots: classic, big, irregular white dots and pinpoint white dots. Classic white dots represent areas of perifollicular fibrosis and are observed most commonly in lichen planopilaris. Pinpoint white dots correspond to hair follicle openings and eccrine gland openings, observed within pigmented background. They are present in patients with dark skin phototypes, regardless of hair loss.
Red dots are described in discoid lupus erythematosus and are considered a good prognostic finding, indicating possible hair regrowth.
Regularly distributed gray or brown-gray dots are a characteristic finding in the eyebrow area of patients with frontal fibrosing alopecia.
Evaluation of Perifollicular Epidermis
Abnormalities of scalp skin color or structure that may be visualized by trichoscopy include scaling, changes in color, abnormalities in skin surface structure, and presence of discharge. A new classification of these abnormalities is presented in Box 1 , which indicates the clinical significance of individual abnormalities.
- •
Scaling
- ○
Diffuse
- ▪
White (psoriasis, discoid lupus erythematosus, allergic dermatitis, dry skin)
- ▪
Yellowish (seborrheic dermatitis, discoid lupus erythematosus, ichthyosis)
- ▪
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Perifollicular
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Color of scales
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White (lichen planopilaris)
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Yellowish (folliculitis decalvans)
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Shape of scale arrangement
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Tubular (lichen planopilaris)
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Tubular with collar formation (folliculitis decalvans)
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Color
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Brown areas
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Honeycomb hyperpigmentation (common)
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Perifollicular; peripilar sign (female and male androgenetic alopecia, telogen effluvium, healthy individuals)
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Scattered (discoid lupus erythematosus, actinic keratosis)
- ▪
- ○
White areas (cicatricial alopecia, detached epidermis, edema)
- ○
Pink, strawberry ice cream–color areas (early fibrosis in cicatricial alopecia)
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Yellow areas (dissecting cellulitis, follicular pustules, bacterial infection)
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Red (inflammation, extravasation, erosion, vascular abnormalities)
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Violaceous blue (lichen planopilaris, discoid lupus erythematosus)
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Discharge
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Yellow and yellow-red (folliculitis decalvans, bacterial infections, dissecting cellulitis, tinea capitis)
- ○
White follicular spicules (monoclonal gammopathy)
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Surface structure
- ○
Starburst pattern hyperplasia (folliculitis decalvans)
- ○
Evaluation of Blood Vessels
Appearance of cutaneous microvessels in trichoscopy may vary in type, arrangement, and number, depending on disease. Analysis of blood vessel arrangement is of special importance in differential diagnosis of inflammatory scalp diseases, such as scalp psoriasis, seborrheic dermatitis, or discoid lupus erythematosus.
Differential diagnosis of nonscarring alopecia
Telogen Effluvium
The term, telogen effluvium , refers to a wide range of clinical situations with the common feature of abrupt, generalized shedding of telogen hairs. It is considered the most common type of hair loss, but only limited evidence-based knowledge is available.
Trichoscopy findings in telogen effluvium include presence of empty hair follicles, predominance of follicular units with only 1 hair, perifollicular discoloration (peripilar sign), and upright regrowing hairs ( Fig. 1 , Table 1 ). Trichoscopy results do not differ depending on the factor that induced telogen hair loss.
| Telogen Effluvium | Androgenetic Alopecia | |
|---|---|---|
| Follicular units with only 1 hair | + | ++ |
| Upright regrowing hairs | ++ | ± |
| Perifollicular discoloration (peripilar sign) | + | ++ |
| Vellus hairs | − | + |
| Hair shaft thickness heterogeneity | − | + |
| Predominance of abnormalities in the frontal region | − | + |
Androgenetic Alopecia
Male androgenetic alopecia and female androgenetic alopecia share similar trichoscopy features. Hair shaft thickness heterogeneity, with simultaneous presence of thin, intermediate, and thick hairs, is the most characteristic feature of androgenetic alopecia. It has been shown that hair diameter diversity reflects follicle miniaturization in androgenetic alopecia. Hair thickness may be estimated when performing trichoscopy with a handheld dermoscope. With this method, hair shafts may classified as thin, intermediate, or thick. Some digital videodermoscopes possess software that allows detailed evaluation of hair shaft thickness in micrometers. Detailed evaluation of hair shaft thickness is not necessary for diagnosis and differential diagnosis in clinical practice but may be useful for monitoring treatment efficacy and is indispensable for clinical trials.
Another trichoscopy feature of androgenetic alopecia is increased proportion of vellus hairs. The proportion of vellus hairs in the frontal scalp area of patients with female androgenetic alopecia is 20.9% ± 12%. This is significantly more than the 6.15% ± 4.6% in healthy volunteers. Multiple vellus hairs may be also present in severe alopecia areata. Thus, sole presence of vellus hairs should not be mistaken for androgenetic alopecia.
The number of hairs in 1 follicular unit is decreased in androgenetic alopecia. Follicular units with only 1 hair predominate in these patients, especially in a late phase of disease. In the frontal area of patients with female androgenetic alopecia, average percentage of follicular units with only 1 hair is 65.2% ± 19.9%. The corresponding number in healthy individuals is 27.3% ± 13%. The percentage of follicular units with only 1 hair is also increased in telogen effluvium (39.0% ± 13.4%) and in various forms of anagen hair loss.
The authors’ experience and study results of show presence of yellow dots a constant finding in androgenetic alopecia, but literature data are inconsistent.
In different studies, yellow dots were observed in 66%, 30.5%, 10% to 26%, and 7% of patients with androgenetic alopecia. The authors find an explanation for this discrepancy in that in androgenetic alopecia some yellow dots have only sebaceous content and not keratosebaceous material, as in other diseases. These sebaceous yellow dots may be washed away by a vigorous hair wash. Accordingly, when patients come for a trichoscopy examination directly after washing their hair, these yellow dots may not be detectable. In the authors’ practice, in patients with noncicatricial alopecia, trichoscopy is always performed together with a trichogram. For this reason, patients are asked to not wash their hair for 3 days before examination. The small, sebaceous yellow dots may develop during these 3 days. This hypothesis is partly confirmed by the authors’ unpublished observations, showing that the number of sebaceous yellow dots in androgenetic alopecia is higher before than after hair washing. No other trichoscopy features depend on hair washing.
Brown perifollicular discoloration (peripilar sign) is observed in 20% to 66% of patients with androgenetic alopecia. A proportion of 32.4% ± 4.7% hair follicle openings are affected. This feature may be also observed in some patients with telogen effluvium and in healthy individuals with the difference that in androgenetic alopecia the proportion of affected hair follicle openings is higher in the frontal compared with the occipital area. In healthy individuals and in patients with telogen effluvium, the proportion of affected hair follicle openings is significantly lower and the distribution is proportional in all scalp areas. Table 1 summarizes the major differences between androgenetic alopecia and telogen effluvium. Fig. 2 presents major trichoscopy features of androgenetic alopecia.
