Overview of dermoscopy of the hair and scalp

INTRODUCTION — Hair and scalp dermoscopy, also known as trichoscopy, is a useful, noninvasive, adjunctive tool for the diagnosis of alopecia and other scalp and hair disorders. The utility of dermoscopy resides in improved visualization of abnormalities of follicular ostia, perifollicular skin, cutaneous blood vessels, and hair shafts. In addition, dermoscopy may aid in the selection of a biopsy site when pathologic examination of a scalp disorder is warranted.

The dermoscopic evaluation of scalp and scalp hair disorders will be reviewed here. The dermoscopic features observed in select hair disorders are reviewed in a table and discussed in topics dedicated to specific hair diseases (table 1).

●Androgenetic alopecia (see "Male pattern hair loss (androgenetic alopecia in males): Pathogenesis, clinical features, and diagnosis", section on 'Physical examination' and "Female pattern hair loss (androgenetic alopecia in females): Pathogenesis, clinical features, and diagnosis", section on 'Dermoscopy')

●Alopecia areata (see "Alopecia areata: Clinical manifestations and diagnosis", section on 'Physical examination')

●Central centrifugal cicatricial alopecia (see "Central centrifugal cicatricial alopecia", section on 'Dermoscopy')

●Dissecting cellulitis of the scalp (see "Dissecting cellulitis of the scalp", section on 'History and physical examination')

●Folliculitis decalvans (see "Folliculitis decalvans", section on 'Dermoscopy')

●Lichen planopilaris (see "Lichen planopilaris", section on 'Dermoscopy')

●Tinea capitis (see "Tinea capitis", section on 'Dermoscopy')

●Traction alopecia (see "Traction alopecia", section on 'Physical examination')

Overviews of dermoscopy and the evaluation and diagnosis of patients with hair loss are provided separately.

●(See "Overview of dermoscopy".)

●(See "Evaluation and diagnosis of hair loss".)

TECHNIQUE — Dermoscopic examination of the hair and scalp provides improved visualization of epidermal and dermal structures through magnification and reduction of the skin surface reflection of light. Most handheld dermatoscopes provide 10-fold magnification; digital dermatoscopes can provide up to 50-fold magnification [1].

Dermoscopic examination can be performed using instruments that emit polarized light or nonpolarized light. Examination with polarized light reduces skin surface reflection through the use of two orthogonally placed filters in a process called cross-polarization. Examination with nonpolarized light requires use of an immersion fluid (eg, alcohol or water) to reduce skin surface reflection. (See "Overview of dermoscopy", section on 'Dermoscopy physics' and "Overview of dermoscopy", section on 'Types of dermatoscopes'.)

Dry dermoscopy (polarized or nonpolarized dermoscopy without use of an immersion fluid) is particularly useful for the evaluation of cicatricial (scarring) alopecias because it allows for evaluation of scales and other features that are associated with disease activity, such as peripilar casts and keratotic plugs. These features are not seen when an immersion fluid is utilized. Thus, when examining patients with patchy alopecia, scalp itching, or possible hairline recession, all of which are features that may occur in both cicatricial and noncicatricial alopecia, examination with dry dermoscopy prior to the application of an immersion fluid is prudent.

Use of an immersion fluid, either alcohol or water, facilitates visualization of vascular patterns in inflammatory scalp diseases, such as psoriasis and seborrheic dermatitis [2-5].

NORMAL DERMOSCOPIC PATTERNS — Familiarity with normal features aids in the recognition of abnormalities of the follicular ostia, perifollicular skin, cutaneous blood vessels, and hair shafts. (See 'Abnormal dermoscopic patterns' below.)

Follicular ostia — Normal follicular ostia appear as small, circular, regularly spaced structures that are commonly referred to as "dots." Most normal follicular units contain two or three hair shafts emerging from the same follicular ostium [6]. Follicular units composed of only one hair shaft are also present but become more prevalent with aging and certain hair disorders, such as androgenetic alopecia and central centrifugal cicatricial alopecia (picture 1).

Perifollicular skin — The examination of normal perifollicular skin is fairly unremarkable. Mild diffuse scaling is a common finding that may be incidental or associated with use of hair products, such as gels [1]. In moderately to highly pigmented skin (eg, tanned skin or skin phototypes IV to VI (table 2)), the normal scalp shows a honeycomb-like pigment network characterized by pigmented lines surrounding round, hypochromic areas that resemble pinpoint white dots (picture 2) [7]. These dots are 0.2 to 0.3 mm in diameter and are regularly distributed between follicular units. The dots correspond to sweat gland ostia and empty follicular ostia. The presence of pinpoint white dots makes the loss of follicular ostia in cicatricial alopecia difficult to appreciate. (See 'Utility' below.)

Blood vessels — Normal scalp vessels appear as interfollicular simple red loops and arborizing red lines. The simple red loops correspond to vessels of the dermal papilla, and arborizing red lines correspond to the subpapillary vascular plexus.

Hair shafts — Dermoscopic examination of scalp hair will reveal both terminal and vellus hairs (picture 3). Normal terminal hairs have a consistent diameter and color along the length of the hairs. Vellus hairs are shorter and narrower than terminal hairs. In the normal scalp, vellus hairs account for less than 20 percent of all scalp hairs [4]. (See "Evaluation and diagnosis of hair loss", section on 'Hair types'.)

ABNORMAL DERMOSCOPIC PATTERNS — The abnormal dermoscopic features detected in scalp and hair disorders can correlate with pathologic features and aid in narrowing the differential diagnosis. Abnormal dermoscopic patterns of the follicular ostia, perifollicular skin, blood vessels, and hair shafts and potential associated disorders are reviewed below (table 1).

Follicular ostia — A variety of abnormal features can occur within follicular ostia. Examples and associated pathologic findings and disorders include [3]:

●Absence/reduction of follicular ostia:

•Dermoscopic findings – Loss of follicular ostia (picture 4A-B)

•Pathologic correlation – Fibrosis

•Associated disorders – Cicatricial alopecias

●Black dots:

•Dermoscopic findings – Round, black dots within ostia (picture 5A-B)

•Pathologic correlation – Broken hair shafts

•Associated disorders – Alopecia areata, dissecting cellulitis, tinea capitis, trichotillomania

●Blue-gray dots:

•Dermoscopic findings – Blue-gray dots in speckled or target pattern within ostia (picture 6)

•Pathologic correlation – Melanophages in papillary dermis

•Associated disorders – Discoid lupus erythematosus (speckled pattern), lichen planopilaris (target pattern)

●Empty follicles:

•Dermoscopic findings – Small depressions without hairs

•Pathologic correlation – Absence of hair within follicular infundibula

•Associated disorders – Androgenetic alopecia, telogen effluvium

●Follicular keratotic plugging:

•Dermoscopic findings – Keratin within follicular ostia (picture 5B-D)

•Pathologic correlation – Hyperkeratosis resulting in keratin plugs within follicular ostia

•Associated disorders – Discoid lupus erythematosus, dissecting cellulitis of the scalp

●Hair tufting:

•Dermoscopic findings – More than five hairs emerging from a single ostium (picture 7)

•Pathologic correlation – Fusion of outer root sheaths of adjacent follicles

•Associated disorder – Acne keloidalis, folliculitis decalvans

●Red dots:

•Dermoscopic findings – Erythematous, polygonal or concentric structures within or around follicular ostia (picture 8)

•Pathologic correlation – Dilated infundibula with peripheral dilated vessels and red blood cell extravasation

•Associated disorder – Discoid lupus erythematosus

●Yellow dots:

•Dermoscopic findings – Round or polycyclic, yellow to yellow-pink dots (often not visible in patients with moderately to highly pigmented skin) (picture 9)

•Pathologic correlation – Dilated infundibula filled with sebum and keratin

•Associated disorders – Alopecia areata, androgenetic alopecia, congenital hypotrichosis, dissecting cellulitis of the scalp, trichotillomania

Perifollicular skin — Abnormalities of perifollicular skin that may aid in diagnosis include the peripilar sign, peripilar white halo, scale, and white patches [3]:

●Peripilar sign:

•Dermoscopic findings – Brown halo around follicular ostia

•Pathologic correlation – Inflammation around the upper follicle

•Associated disorder – Androgenetic alopecia

●Peripilar white halo:

•Dermoscopic findings – Gray-white halo around follicular ostia (picture 10)

•Pathologic correlation – Concentric fibrosis

•Associated disorder – Central centrifugal cicatricial alopecia

●Scale:

•Dermoscopic findings – Diffuse or perifollicular scale (picture 5D)

•Pathologic correlation – Hyperkeratosis

•Associated disorders – Normal scalp (mild, diffuse scale), psoriasis (white scale and twisted capillaries (picture 11)), seborrheic dermatitis (yellow and white scale and arborizing vessels (picture 12)), lichen planopilaris (peripilar scale (picture 4A-B)), folliculitis decalvans (peripilar and interfollicular scale (picture 7)) (see 'Hair shafts' below)

●White patches:

•Dermoscopic findings – Irregularly distributed white patches of different sizes and shapes interspersed with pinpoint white dots (picture 13), mostly seen in highly pigmented skin (phototypes IV to VI (table 2))

•Pathologic correlation – Fibrosis

•Associated disorder – Cicatricial alopecias

Blood vessels — Dermoscopic features of scalp blood vessels that may aid in diagnosis include:

●Enlarged branching vessels:

•Dermoscopic finding – Enlarged, tortuous, and dilated vessels

•Pathologic correlation – Dilated capillaries in papillary dermis

•Associated disorders – Connective tissue disorders (discoid lupus erythematosus, dermatomyositis)

●Increased number of arborizing vessels:

•Dermoscopic finding – Branching vessels (picture 5C).

•Pathologic correlation – Proliferation of vessels in the subpapillary vascular plexus.

•Associated disorder – Arborizing vessels are a feature of a normal scalp but are increased in number in seborrheic dermatitis and contact dermatitis.

●Twisted red loops:

•Dermoscopic finding – Seen at magnification ≥40x as twisted glomerular vessels (picture 14), these appear as red dots at low magnification.

•Pathologic correlation – Enlarged and dilated capillaries in papillary dermis.

•Associated disorders – Folliculitis decalvans, psoriasis.

Hair shafts — Examples of hair shaft abnormalities associated with scalp disease include [3]:

●Broken hairs:

•Dermoscopic findings – Broken hairs of different lengths (picture 15)

•Associated disorders – Alopecia areata, hair fragility disorders, tinea capitis, trichotillomania, woolly hair

●Circle hairs:

•Dermoscopic findings – Short, thin hairs forming a circle (picture 16)

•Associated disorders – Alopecia areata (numerous circle hairs), androgenetic alopecia

●Coiled hairs:

•Dermoscopic findings – Curled, broken hairs

•Associated disorder – Trichotillomania

●Comma hairs:

•Dermoscopic findings – Short, C-shaped hairs (picture 17A-B)

•Associated disorder – Tinea capitis

●Corkscrew hairs:

•Dermoscopic findings – Short, spiral-shaped hairs (picture 17B)

•Associated disorder – Tinea capitis (scalp hair), scurvy (body hair) [8]

●Exclamation point hairs:

•Dermoscopic findings – Short, tapered hairs (narrower proximal end) (picture 5A)

•Associated disorders – Alopecia areata

●Hair diameter variability:

•Dermoscopic findings – Terminal hair shafts of varying diameter (picture 18A-B)

•Associated disorder – Androgenetic alopecia

Examples of other acquired hair shaft abnormalities include [9]:

●Bubble hair:

•Dermoscopic findings – Clear, oval spaces within hair shaft

•Associated disorder – Exposure of hair shaft to excessive heat (eg, hair dryer, curling iron)

●Nits:

•Dermoscopic findings – Viable eggs (brown, ovoid structures with a convex end) and empty egg cases (translucent structures with flat end) attached to one side of hair shaft (picture 19A-C) [10]

•Associated disorder – Pediculosis capitis

●Peripilar casts:

•Dermoscopic findings – White to brown, cylindric structures with spindled edges around proximal hair shafts (traction alopecia (picture 20)), white to yellow scale loosely adherent to hair shafts (psoriasis, seborrheic dermatitis), tightly adherent scale to the proximal hair shaft (lichen planopilaris (picture 4A-B), folliculitis decalvans (picture 7))

•Associated disorders – Folliculitis decalvans, lichen planopilaris, psoriasis, seborrheic dermatitis, traction alopecia

●Pseudocasts:

•Dermoscopic findings – Irregularly shaped concretions with variable length and thickness (hair product residue) (picture 21) [11], yellow or beige nodules or sheaths (white piedra), dark nodules (black piedra), yellow concretions (trichomycosis capitis (picture 22))

•Associated disorder – Hair product residue (eg, hair spray, dry shampoo), piedra, trichomycosis capitis

●Trichoptilosis (split ends):

•Dermoscopic findings – Longitudinal splitting of distal hair shaft (picture 23)

•Associated disorder – Weathering of hair shaft

●Trichorrhexis nodosa:

•Dermoscopic findings – White nodules and fractured or frayed ends of hair (picture 24)

•Associated disorder – Mechanical, chemical, or thermal damage to hair shaft

Examples of abnormalities seen in congenital hair disorders associated with hair fragility include [9]:

●Monilethrix:

•Dermoscopic findings – Regularly spaced beading of hair shaft caused by nodes (medulla present) and internodes (medulla absent) (picture 25)

•Associated disorder – Monilethrix

●Pili torti:

•Dermoscopic findings – Sharp bending of hair shaft at irregular intervals visible at low magnification (20x), twisting of hair shaft at irregular intervals visible at higher magnification (picture 26)

•Associated disorders – Various causes (rare genetic disorders, occasional occurrence in cicatricial alopecia)

●"Tiger-tail" pattern:

•Dermoscopic findings – Pattern of alternating light and dark bands within hair shaft not visible with standard dermoscopy; however, use of a polarized transilluminating dermoscopy technique that involves either two dermatoscopes plus a light-emitting diode from a cellular phone or a single dermatoscope and a mirror may allow for recognition of this characteristic finding [12].

•Associated disorder – Trichothiodystrophy.

●Trichorrhexis invaginata:

•Dermoscopic findings – Bamboo hairs (knots in hair shaft demonstrating ball and cup-like morphology), broken hairs with cupped ends ("golf-tee hairs") or ball-shaped ends ("matchstick hairs")

•Associated disorder – Netherton syndrome

Examples of hair shaft abnormalities in hair disorders not associated with hair fragility include [9]:

●Pili annulati:

•Dermoscopic finding – Alternating white bands within hair shaft (air-filled cavities) (picture 27)

•Associated disorder – Pili annulati

●Pili trianguli and canaliculi:

•Dermoscopic findings – Triangular or kidney-shaped hair shaft with longitudinal groove or flattening

•Associated disorder – Uncombable hair syndrome

●Woolly hair:

•Dermoscopic finding – Hair shafts with crawling snake configuration with short wave cycles, broken hairs

•Associated disorder – Hereditary woolly hair, familial woolly hair, woolly hair nevus

APPROACH TO EXAMINATION — Dermoscopic examination is a useful, adjunctive diagnostic tool (table 1). Dermoscopic findings may narrow the differential diagnosis, support or confirm a suspected diagnosis, or support the need for further pathologic, microbiologic, or other testing.

Utility — Dermoscopy can be useful for differentiating cicatricial and noncicatricial forms of alopecia. The loss of follicular ostia is a characteristic finding of cicatricial alopecia (picture 4A-B). Although loss of follicular ostia may not be prominent in early-stage disease that lacks patches of alopecia, dermoscopy can identify other supportive findings of cicatricial alopecia, such as peripilar casts or absence of vellus hairs. In addition, loss of follicular ostia is difficult to appreciate in patients with moderately to highly pigmented skin (eg, skin phototypes IV to VI (table 2)) due to the presence of numerous pinpoint white dots representative of both follicular openings and sweat gland ostia (picture 10). However, features such as an irregular distribution of pinpoint white dots and presence of white patches support the diagnosis of cicatricial alopecia. (See 'Abnormal dermoscopic patterns' above.)

Dermoscopy can also aid in differentiating common hair shedding disorders (eg, telogen effluvium, androgenetic alopecia) from each other and from hair breakage secondary to hair fragility. Hair diameter variability is a characteristic finding of androgenetic alopecia that is absent in telogen effluvium (picture 18A-C). Empty follicles support hair shedding, whereas hair shaft abnormalities associated with increased hair fragility (eg, trichorrhexis nodosa) are supportive of hair breakage. (See 'Hair shafts' above and 'Follicular ostia' above.)

Many cicatricial and inflammatory disorders of the scalp are associated with erythema or scale. Dermoscopy can aid in visualizing these features and may identify signs that are helpful for diagnosis, such as particular vascular patterns and the distribution of scale (eg, peripilar versus diffuse scale). (See 'Perifollicular skin' above and 'Blood vessels' above and 'Hair shafts' above.)

In the past, assessment of many congenital or acquired hair shaft disorders required plucking or clipping of hairs and light microscopic or electron microscopic examination of hair shafts. Dermoscopy facilitates rapid identification of multiple congenital and acquired hair shaft disorders. (See 'Hair shafts' above and 'Examination of hair shafts' below.)

Dermoscopy also can help to identify structures adherent to the hair shaft. The magnified view facilitates differentiation of structures such as nits (picture 19A), peripilar casts (picture 20), and hair concretions (picture 22), as may be seen in disorders such as pediculosis capitis, traction alopecia, and trichomycosis capitis, respectively. Pseudocasts, which result from hair spray or dry shampoo residue, may also be identified with dermoscopy (picture 21) [11]. (See 'Hair shafts' above.)

Examination of the scalp — Dermoscopic examination of the scalp is facilitated by parting of the hair. The ideal site(s) for examination are determined by the suspected disorder(s). In patients with suspected cicatricial alopecia, examination of the center of an alopecic patch is often useful for assessing for loss of follicular ostia, whereas examination of the periphery of a patch of alopecia is often the best for assessing for features of active disease (eg, erythema, peripilar casts, follicular plugging, etc). Examination of the frontal hairline is helpful for diagnosis of frontal fibrosing alopecia (picture 28).

Examination of hair shafts — Dermoscopic examination of hair shafts can be performed on hairs that remain lodged in the scalp or hairs that have been pulled out, plucked, or cut. In patients in whom the color contrast between scalp and hair is low (eg, dark brown skin and black hair) or with markedly curly hair (eg, Afro-textured hair), examination of plucked hairs may allow for better visualization of hair shafts than in vivo examination of hairs [9]. Pulling hairs also allows for examination of hair roots, a feature that can be useful for determining the type of hairs being shed (eg, telogen versus anagen). Placement of hair shafts on a piece of paper with a color that contrasts with the patient's hair color facilitates examination of pulled, plucked, or cut hairs.

If androgenetic alopecia is suspected, it is helpful to compare findings in characteristically affected and unaffected areas. For example, in females, the hair should be parted and examined at the vertex, mid scalp, and frontal scalp (2 cm from hairline). The degree of hair diameter diversity detected in these areas can be compared with a typically unaffected site, such as the occipital scalp. (See "Female pattern hair loss (androgenetic alopecia in females): Pathogenesis, clinical features, and diagnosis" and "Male pattern hair loss (androgenetic alopecia in males): Pathogenesis, clinical features, and diagnosis".)

DERMOSCOPY-GUIDED BIOPSY — When a biopsy is necessary to confirm the diagnosis, dermoscopy can help with identifying the most appropriate site for biopsy. Dermoscopy allows for more accurate assessment of sites of disease activity, which can be particularly helpful for pathologic diagnosis of cicatricial alopecias. As examples, follicular units exhibiting peripilar casts, a gray-white halo, hair tufts, or follicular red dots may be preferred biopsy sites for the diagnosis of lichen planopilaris, central centrifugal cicatricial alopecia, folliculitis decalvans, and discoid lupus erythematosus, respectively [13].

FEATURES OF SPECIFIC DIAGNOSES — Dermoscopic features associated with specific hair and scalp disorders are reviewed in a table (table 1).

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dermoscopy".)

SUMMARY AND RECOMMENDATIONS

●Overview – Dermoscopy of the hair and scalp (also known as trichoscopy) is a noninvasive adjunctive tool for the diagnosis of a variety of hair and scalp disorders (table 1). Dermoscopy magnifies structures in the epidermis and dermis and allows for better visualization of follicular ostia, perifollicular skin, cutaneous blood vessels, and hair shafts. (See 'Introduction' above and 'Technique' above and "Overview of dermoscopy".)

●Role in diagnosis – Clinicians utilizing dermoscopy should be familiar with the normal dermoscopic patterns of the scalp and hair. Abnormalities in dermoscopic patterns often correlate with pathologic features and can narrow the differential diagnosis for hair and scalp diseases (see 'Normal dermoscopic patterns' above and 'Abnormal dermoscopic patterns' above):

•Scarring and nonscarring alopecia – Dermoscopic examination can be helpful for distinguishing cicatricial from noncicatricial alopecia and androgenetic alopecia from telogen effluvium. Dermoscopy is also helpful for identifying particular features of cicatricial and inflammatory disorders of the scalp that aid in diagnosis, such as the appearance of follicular ostia, vascular patterns, and the distribution of scale. (See 'Abnormal dermoscopic patterns' above and 'Utility' above.)

Dermoscopy may aid in the selection of a biopsy site in the evaluation of cicatricial alopecia. (See 'Dermoscopy-guided biopsy' above.)

•Hair shaft disorders – In the past, the diagnosis of many congenital and acquired hair shaft disorders required plucking or clipping of hairs and light microscopy or electron microscopy of the hair shafts. Dermoscopy allows for rapid identification of these disorders and often can be performed without plucking or clipping hair shafts. (See 'Utility' above and 'Hair shafts' above and 'Examination of hair shafts' above.)

●Site selection – The optimal sites for the examination of scalp disorders are dependent upon the disorders in the differential diagnosis. In the evaluation of androgenetic alopecia, comparing involved and uninvolved areas of the scalp is helpful for confirming the diagnosis. (See 'Examination of the scalp' above.)