Histopathological evaluation is crucial in diagnosing scalp disorders. Scalp biopsies provide reliable information in delineating various cicatricial and non-cicatricial alopecias. Residents need to know normal hair structures to detect pathologies easily, and should be well-versed in choosing the correct biopsy site, biopsy technique, specimen processing, and the normal pathology of the hair follicle unit; how to recognize the type of hair (terminal, intermediate, and vellus hair) and the stage of hair (anagen, catagen, and telogen) follicle. This helps not only in interpreting scalp histopathology but also in understanding the tumors of folliculo-sebaceous-apocrine origin.
Choosing the appropriate area for scalp biopsy
In cases of scarring alopecia, biopsies from the center of alopecia or scarred area reveal scarring and destruction of hair follicles without any identifiable pathology. Ideally, the biopsies should be taken from the periphery of the alopecia patch; however, not all follicles within the active margin will be affected in the initial stages; hence, choosing an appropriate site is essential. Trichoscopy can guide the choice of area for the biopsy. Table 1 shows the ideal site for biopsy in both scarring and non-scarring alopecias.[1]
Table 1.
Site of biopsy in scarring and non-scarring alopecias
| Scalp pathology | Site for biopsy | |
|---|---|---|
|
| ||
| Clinical | Dermoscopic | |
| Scarring alopecia | ||
| Discoid lupus erythematosus | At the periphery of plaque with erythematous zone and follicular plugs | Yellow-brown follicular keratotic plugs Red dots on trichoscopy |
| Lichen planopilaris and Frontal fibrosing alopecia | At the active new patch, from the periphery with scaling and violaceous papules | Peripilar cylindrical scale at the emergence of the hair follicle |
| Folliculitis decalvans | Tufts of hair (doll hair appearance) and area of pustules | Tufts of six or more hairs surrounded by thick white, yellowish casts, and erythema |
| Central centrifugal cicatricial alopecia | Areas with erythema and scaling at the progressive periphery of the patch | Single hairs or groups of two hairs surrounded by a peripilar grey-white halo |
| Non scarring alopecia | ||
| Androgenetic alopecia | Frontotemporal area in males and central partition in females with variable hair diameter | Area of miniaturization, diameter diversity such as frontotemporal (sideburn) area in males, frontal (central partition) in females |
| Alopecia areata | Areas where the hair pull test is positive, the periphery of the active patch | Areas of miniaturization, exclamation hairs, broken hairs, and black dots |
| Trichotillomania | Alopecia patch with variable hair length | Areas with perifollicular hemorrhage, hair dust, and empty follicular orifices |
| Telogen effluvium | Areas of regrowing hairs or thinned-out zone | Area with single follicular units, variable hair shaft diameter |
Biopsy technique
Biopsy, if possible, should be taken from areas which are less likely to cause cosmetic disturbance, such as the frontal area and hair margins. At the chosen biopsy site, hairs are clipped, preferably shaved, and later infiltrated with local anesthesia (lidocaine 1% with adrenaline (1:10,000 dilution)) with a waiting period of 10 minutes. A 4 mm punch biopsy is done, along the direction of the emergence of hair, to minimize the transection of the hair follicle unit. The biopsy site is closed with simple interrupted closure with 4-0 to 3-0 reverse cutting, blue-colored prolene suture with no requirement of wound dressing. The suture is removed after ten days.[2] Circumferential pressure applied using the ring handle of the hemostat can prevent excess bleeding and improve visualization for optimal punch biopsy.[3] A simple and effective technique for easier clipping includes the application of petrolatum to scissors, cutting the hairs close to the scalp, and then wiping the petrolatum and hairs from scissors.[4] Use of preliminary horizontal mattress suture is also advised to achieve rapid hemostasis are some of the modification in scalp biopsy technique.[5]
Current guidelines follow St John’s Protocol, where two biopsies of 4 mm are procured in the non-scarring type, and both biopsies are sectioned horizontally. In contrast, one sample is sectioned horizontally and the other vertically for scarring alopecia. The second tissue bit, before transferring, is further bisected and put in formalin and Michel’s medium for histopathology and direct immunofluorescence (DIF), respectively [Figure 1a].[6] In the Tyler technique, the entire specimen is dissected vertically into two halves. One half is horizontally sectioned. The disadvantage of this technique is reduced hair density [Figure 1b].[7] In the HoVert (Horizontal Vertical) technique, the tissue specimen is transected horizontally 1 mm below the epidermis. This epidermal portion is bisected vertically. These two vertical sections show follicular and interfollicular epithelium, dermo-epidermal junction, papillary dermis, and superficial part of the follicle. The dermal/subcutaneous portion is bisected transversely at the dermo-subcutaneous junction. The horizontal section at the superficial reticular dermis and subcutis allows visualization of all the follicular units, superficial reticular dermis, terminal hair, and upper subcutis, respectively. If the biopsy is too thin, then the first step of the transverse section is done, and then the upper portion is vertically bisected, and the lower portion is not transected to preserve follicular structures at the dermal subcutis level [Figure 1c].[8]
Figure 1.
(a) Pictorial representation of St John’s technique. (b) Pictorial representation of Tyler technique. (c) Pictorial representation of Hovert technique
Horizontal biopsy
Horizontal biopsies are recommended in both scarring and non-scarring types, and sections are taken at various levels: bulb, isthmus, and infundibulum. The bulbar area is identified by the presence of dermal mesenchymal cells, matrical cells admixed with pigmented melanocytes, and is located at the level of subcutaneous or dermis-subcutaneous junction in the case of terminal hair and at the level of mid-dermis in case of vellus hair. A cross-section of the hair bulb reveals the dermal papilla, matrical cells, pigmented melanocytes, and the nucleated hair shaft, which is surrounded by an inner root sheath (IRS), recognized by a structureless intensely eosinophilic area [Figure 2a]. IRS is covered by the pale glycogenated outer root sheath (ORS) with preserved cytological morphology and dermal fibrous sheath. The ORS cells have a well-demarcated cell outline, and lie vertically on the basement membrane. The isthmic area is recognized by degenerated or an absent inner root sheath and the presence of sebaceous glands around it [Figure 2b]. Isthmic epithelial cells are characterized by pink cytoplasm and indistinct cell outline.[9] At the level of the sub-isthmus, the hair shaft is anucleated, IRS is completely keratinized (pink hyalinized), and the ORS is less pale and more eosinophilic with loss of cellular delineation. Upon entering the isthmus, abrupt disintegration of the keratinized IRS occurs and is replaced by trichilemmal keratinization by the ORS. At the infundibular area, the epithelium is matured and is similar to the epidermis.[10]
Figure 2.
(a) Histopathology depicts the bulbar region on the horizontal section, which shows dermal mesenchymal cells and pigmented melanocytes. The blue arrow depicts pigmented melanocytes in the bulb [H and E, ×100]. (b) Isthmic region on the horizontal section, with an absent to disintegrating inner root sheath and the presence of sebaceous glands [H and E, ×50]. (c) Vertical section of terminal hair depicting infundibulum, isthmus, supra bulbar, and bulbar region [H and E, ×50]. (d) Vertical section showing dermal fibrous streak below the hair follicle [H and E, ×100]. (e) Vertical section of terminal catagen hair depicts apoptotic epithelial cells and eosinophilic thickened basement membrane [H and E, ×400]. (f) Horizontal section of terminal catagen hair shows a thickened basement membrane and apoptotic area [H and E, ×400]
Vertical biopsy
Vertical scalp biopsies have a limited number of follicular units (2 to 3 follicles in a 4 mm punch) and reveal both follicular and interfollicular pathology. This technique does not reveal the follicular density, hair cycle, and miniaturization, making it difficult to interpret non-cicatricial alopecias. The infundibulum, isthmus, suprabulbar, and bulbar areas are analyzed in detail in this sectioning [Figure 2c].[7] Table 2 summarizes the advantages and disadvantages of horizontal and vertical sectioning of scalp biopsy specimens.[6,7,11]
Table 2.
Advantages and disadvantages of horizontal and vertical sectioning
| Horizontal section | Vertical section |
|---|---|
| Ideal for non-scarring alopecia | Adequate for both scarring and non-scarring alopecia. |
| It includes more hair follicle units | Less hair follicle unit visualized |
| Quantitative assessment of inflammatory infiltrate is better appreciated in the horizontal section. | For scarring alopecia, the entire thickness of the skin can be examined at a single glance In lichen planopilaris and discoid lupus erythematosus, the inflammatory infiltrate is restricted to the dermo-epidermal junction, which may be missed in horizontal sections |
Miniaturization of terminal follicles is detected in both horizontal and vertical biopsies. Histological features of long-standing diseases such as fibrous tracts, follicular destruction, and atrophy of sebaceous glands are detected in both sections
In scalp biopsies, various phases of the hair cycle, such as anagen, catagen, and telogen terminal hair, are present. The catagen stage is characterized by papillae not enclosed by the follicle, a 50% reduction in the volume of dermal papillae, dermal streamer (Arao perkin bodies) on the vertical section, apoptotic epithelial cells, thickened basement membrane (eosinophilic glassy membrane) without the hair follicle on cross-section [Figure 2d-f]. Telogen hair includes telogen germinal unit and telogen club hair. At the beginning of the telogen phase, the papillae are a condensed ball of spindle-shaped nuclei with scant stroma referred to as secondary hair germ (telogen germinal unit), which appears as an ‘asterisk’ in cross-section [Figure 3a] and lies below telogen club hair in the vertical section. Telogen club unit is recognized by wrinkling or shedding of the inner root sheath and brightly eosinophilic trichilemmal keratinization, known as flame thrower appearance [Figure 3b and c].[9] Around 92% of scalp hair is in anagen, 1.6% catagen, and 6.2% telogen phase.[7] The follicular units (folliculo-sebaceous-apocrine unit) are the fundamental scalp structures. Each follicular unit comprises 3-5 terminal hairs, 1-2 vellus hairs, arrector pili, and sebaceous and apocrine glands [Figure 3d]. Cross-sections demonstrate 12 to 14 follicular units per sample. The normal anagen-to-telogen hair ratio is 12:1, which is reduced to 5:1 in androgenetic alopecia (AGA).[12] Increased telogen hairs and reduced anagen-to-telogen ratio (8:1) are seen in chronic telogen effluvium (CTE).[13]
Figure 3.
(a) The horizontal section depicts an irregular island of basaloid cells referred to as telogen germinal unit (asterisk-like appearance) [H and E, ×400]. (b) Vertical section of terminal telogen hair shows bright red trichilemmal keratin, giving a ‘flame thrower’ appearance [H and E, ×100]. (c) Vertical section of terminal telogen hair shows a wrinkling of the inner root sheath [H and E, ×100]. (d) Horizontal section depicts a folliculosebaceous unit [H and E, ×100]. (e) Horizontal section demonstrates the inner root sheath, outer root sheath, and hair shaft [H and E, ×100]. (f) Vertical section of vellus hair demonstrates the infundibulum, isthmus, supra bulbar, and bulbar region, and the location is at the level of the mid-dermis [H and E, ×100]
A normal 4-mm punch in a Caucasian, African-American, and Korean (including Asians) has 25–30, 21, and 16 terminal hairs in a transverse section through the deep dermis and five additional vellus hairs through the superficial dermis.[6] Terminal (T) and vellus (V) hairs are differentiated by the hair shaft diameter compared to the inner root sheath diameter, which is less in the latter [Figure 3e]. The location of the hair bulb in the subcutaneous or dermo-subcutaneous junction indicates terminal hair, while the dermis indicates vellus hair [Figure 3f]. A normal T: V ratio is 8:1; this ratio is reduced to 4:1 and 1:1 in AGA and alopecia areata (AA), respectively.[12,14] In CTE, the T: V ratio is more than 8:1.13, while miniaturized hairs are considered terminal hairs, the diameter of the hair shaft is intermediate between terminal and vellus hair, and its location is ascended high up in the dermis.[14]
Interpretation
The diagnostic algorithm to approach scalp alopecias is illustrated in Supplementary Flowchart 1 (242.2KB, tif) .
The first step is identifying the nature of alopecia- scarring or non-scarring. Fibrous tissue replacing the follicular unit or losing sebaceous glands is considered a clue for scarring alopecia.[15]
The second step is to recognize the number of hair follicle units, numbers in anagen, catagen, telogen phases, and anagen: telogen and T: V hair ratios. This is done at the level of the isthmus. While determining ratios, telogen count encompasses telogen club hair, telogen germinal unit, and catagen. Similarly, vellus hairs encompass both vellus and intermediate or miniaturized hairs.[16]
The third step is to look for inflammatory infiltrate. Among non-scarring alopecias, AA is characterized by peribulbar lymphocytic infiltrate [Figure 4a].[14] Among scarring alopecias, lymphocytic infiltrate is seen in discoid lupus erythematosus (DLE) [Figure 4b], lichen planopilaris (LPP), frontal fibrosing alopecia, central centrifugal cicatricial alopecia (CCCA), pseudopelade of Brocq, and alopecia mucinosa; neutrophilic in acne necrotica, erosive pustular dermatosis, and acne keloidalis nuchae, and mixed infiltrate is described in dissecting cellulitis of scalp and folliculitis decalvans.[17]
Figure 4.
(a) Horizontal section depicting trichomalacia and pigment casts [H and E, ×400]. (b) Horizontal section depicting empty hair follicle [H and E, ×400]. (c) Peribulbar lymphocytic infiltration in a case of alopecia areata [H and E, X400]. (d) Peri-infundibular lymphocytic infiltration in a case of discoid lupus erythematosus [H and E, ×100]
The fourth step is to find specific clues. Melanin pigment casts, trichomalacia [Figure 4c], empty hair follicles [Figure 4d], intrafollicular hemorrhagic casts, folliculocentric hemosiderin, and increased catagen: telogen ratio are seen in trichotillomania.[18] Dystrophic anagen hairs and trichomalacia are sometimes described in AA.[14] Follicular plugs, basal vacuolar degeneration, basement membrane thickening, lichenoid, and superficial and deep perivascular lymphocytic infiltrate with mucin deposit in the deeper dermis are diagnostic of DLE.[19] Hypergranulosis of the affected follicle, Civatte bodies, and superficial perifollicular wedge-shaped lymphocytic infiltrate with the absence of interfollicular mucin are suggestive of LPP.[20] Occasional fusion of infundibula and premature desquamation of the inner root sheath, concentric lamellar fibroplasia (onion skin-like fibrosis) of affected follicles are indicative of CCCA.[21] Mucin deposit in the outer root sheath is suggestive of alopecia mucinosa.[22] The histopathological findings in scarring and non-scarring alopecias are summarized in Table 3. The direct immunofluorescence and special stains help in delineating the differentials in scalp biopsy, which is summarized in Table 4.[19,20,21,22,23,24]
Table 3.
Summary of the histological features of scarring and non-scarring alopecia
| Type of inflammatory infiltrate | Types of alopecia | Histological findings |
|---|---|---|
|
| ||
| Non scarring alopecia | ||
| Alopecia areata (AA) | • Profound miniaturization, catagen telogen shift, focal trichomalacia, necrosis of matrical cells, peribulbar lymphocytic (swarm of bees appearance), and eosinophilic infiltrates (early and characteristic, but less often seen) | |
| • Mimics of AA include non-scarring alopecia of systemic lupus erythematosus, and syphilitic alopecia, which are to be ruled out with clinical and serological analysis | ||
| Androgenetic alopecia | • Follicular miniaturization, preserved but reduced sebaceous lobules, increased vellus hairs, and fibrous streamers | |
| Telogen effluvium | • Increase in telogen hair, fibrous streamers, absence of miniaturization, and inflammation. | |
| Trichotillomania | • Pigment cast, trichomalacia, melanin cast in collapsed fibrous root sheath, peri-and-intrafollicular hemorrhage (hamburger sign), and distorted hair bulb | |
|
| ||
| Scarring alopecia | ||
|
| ||
| Lymphocytic | Discoid lupus erythematosus[7] | • Follicular plugs, basal vacuolar degeneration, basement membrane thickening, lichenoid and superficial and deep perivascular lymphocytic infiltrate and mucin in deeper dermis |
| Lichen planopilaris[8] | • Hypergranulosis of affected follicle, Civatte bodies, superficial perifollicular wedge-shaped lymphocytic infiltrate and absence of interfollicular mucin, arrector pili muscles, and sebaceous glands | |
| Central centrifugal cicatricial alopecia[9] | • Concentric lamellar fibroplasia (onion skin-like fibrosis) of affected follicles, variably dense lymphocytic perifollicular inflammation, primarily at the level of the upper isthmus and lower infundibulum, occasional fusion of infundibula and premature desquamation of the inner root sheath | |
| Alopecia mucinosa[10] | • Mucin deposits in the outer root sheath and dense perifollicular lymphocytic infiltrate | |
| Pseudopelade of Brocq[12] | • Reduced number of terminal hairs and loss of sebaceous glands, perifollicular concentric lamellar fibrosis, and follicular stelae with no overlying follicle | |
| Keratosis follicularis spinulosa decalvans[13] | • Follicular plugging, hypergranulosis, perifollicular fibrosis, and lymphocytic infiltrate. | |
| Neutrophilic | Folliculitis decalvans[10] | • Acute inflammation reveals interfollicular and perifollicular mixed infiltrate of neutrophils, lymphocytes, and plasma cells |
| • Marked inflammation at lower infundibulum | ||
| • Late stage shows perifollicular fibrosis, follicular tufting, and dermal fibrosis | ||
| Dissecting cellulitis[12] | • Early dense lymphocytic perifollicular inflammation at lower half of follicle and subcutis | |
| • Deep abscesses and sinus tracts of neutrophils, lymphocytes, and plasma cells in later disease | ||
| • Characteristic feature—sinus tracts are lined by stratified squamous epithelium | ||
| Mixed | Acne keloidalis[10] | • Early stages show follicular dilation and deeper follicular rupture with perifollicular dense neutrophils, and lymphoplasmacytic infiltrates which is replaced with granuloma at later stages |
| Acne necrotica[14] | • Perifollicular necrotizing lymphocytic infiltrate in early disease | |
| • Late-phase shows follicular necrosis and neutrophils in the superficial dermis | ||
| Erosive pustular dermatosis[12] | • Nonspecific early findings with marked epidermal atrophy and focal erosions | |
Table 4.
| Stain | Findings |
|---|---|
| Verhoeff-Van Gieson | • Allows for a distinction between the normal dermis and scarred areas in later-stage scarring, with scarred areas lacking elastic fibers |
| • A wedge-shaped scar with loss of elastin is seen in LPP | |
| • A broad scar throughout the dermis with the destruction of elastic tissue is observed in DLE Preservation of elastin is a features of pseuopelade of Brocq | |
| • Hyalinization of the dermis with increased and thickened elastic fibers are described in CCCA | |
| Periodic Acid Schiff staining | • Highlights thickened basement membrane zone, apoptotic cells, and fungal elements |
| Toluidine blue | • Visualizing premature desquamation of the inner root sheath: helpful for the diagnosis of CCCA |
| Toluidine blue and colloidal iron | • Demonstrate dermal mucin in DLE and alopecia mucinosa |
| Gram stain | • Done in all neutrophilic and mixed inflammatory scarring alopecia to rule out bacterial infectious etiology |
| Direct immunofluorescence | |
| DLE | • Granular IgG, C3, and/or IgM/IgA deposit at the basement membrane and around the hair follicle |
| LPP | • Grouped globular immunofluorescence, usually IgM, especially when found adjacent to the follicular epithelium |
| Pseudopelade of Brocq | • Usually negative with occasional scant finely granular IgM along the basement membrane zone of the follicular infundibulum |
| Alopecia due to immunobullous disorders | • Positive intercellular staining of Ig with or without C3 in the outer root sheath of anagen hairs of active pemphigus vulgaris and pemphigus foliaceous • The value of the direct immunofluorescence of telogen hairs remains controversial |
| Alopecia areata | • The basement of the lower part of the hair follicle shows C3 and occasionally IgG and IgM deposits |
LPP: Lichen planopilaris, DLE: Discoid lupus erythematosus, CCCA: Central centrifugal cicatricial alopecia, Ig: Immunoglobulin, C: complement
The real scenario in India
Many of the laboratories and institutions do not perform horizontal sectioning, making it obligatory to reach a diagnosis from vertical sectioning.
To conclude, this article aims to summarize the biopsy techniques, identify features of various stages of the hair cycle, and differentiate features of individual scalp pathologies. Cicatricial alopecias share many overlapping features, especially at the end stage, and hence clinicopathological correlation is a must.
Conflicts of interest
There are no conflicts of interest.
Use of artificial intelligence (AI)
No artificial intelligence-assisted tools including large language models, chatbots, or image generator were utilized.
Diagnostic algorithm for histopathological approach of alopecia
Funding Statement
Nil.
References
- 1.Miteva M, Tosti A. Dermoscopy guided scalp biopsy in cicatricial alopecia. J Eur Acad Dermatol Venereol. 2013;27:1299–303. doi: 10.1111/j.1468-3083.2012.04530.x. [DOI] [PubMed] [Google Scholar]
- 2.Madani S, Shapiro J. The scalp biopsy: Making it more efficient. Dermatol Surg. 1999;25:537–8. doi: 10.1046/j.1524-4725.1999.99045.x. [DOI] [PubMed] [Google Scholar]
- 3.Whalen JG, Gehris RP, Kress DW, English JC. Surgical Pearl: Instrument tamponade for punch biopsy of the scalp. J Am Acad Dermatol. 2005;52:347–8. doi: 10.1016/j.jaad.2004.06.042. [DOI] [PubMed] [Google Scholar]
- 4.Kouba DJ, Mamelak AJ. Surgical Pearl: A rapid and effective technique for perioperative hair removal. J Am Acad Dermatol. 2006;55:514–5. doi: 10.1016/j.jaad.2006.02.013. [DOI] [PubMed] [Google Scholar]
- 5.Ingraffea AA. Use of a preliminary horizontal mattress suture on scalp biopsies to achieve rapid hemostasis. Dermatol Surg. 2010;36:1312. doi: 10.1111/j.1524-4725.2010.01629.x. [DOI] [PubMed] [Google Scholar]
- 6.Palo S, Biligi DS. Utility of horizontal and vertical sections of scalp biopsies in various forms of primary alopecias. J Lab Physicians. 2018;10:95–100. doi: 10.4103/JLP.JLP_4_17. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Nguyen JV, Hudacek K, Whitten JA, Rubin AI, Seykora JT. The HoVert technique: A novel method for the sectioning of alopecia biopsies. J Cutan Pathol. 2011;38:401–6. doi: 10.1111/j.1600-0560.2010.01669.x. [DOI] [PubMed] [Google Scholar]
- 8.Mulinari-Brenner F, Souza FH, Fillus Neto J, Torres LF. Quantitative evaluation of transverse scalp sections. An Bras Dermatol. 2006;81:227–32. [Google Scholar]
- 9.Elston D. The ‘tyler technique’ for alopecia biopsies. J Cutan Pathol. 2012;39:306. doi: 10.1111/j.1600-0560.2011.01839.x. [DOI] [PubMed] [Google Scholar]
- 10.Childs JM, Sperling LC. Histopathology of scarring and nonscarring hair loss. Dermatol Clin. 2013;31:43–56. doi: 10.1016/j.det.2012.08.001. [DOI] [PubMed] [Google Scholar]
- 11.Özcan D, Özen Ö, Seçkin D. Vertical vs. transverse sections of scalp biopsy specimens: A pilot study on the comparison of the diagnostic value of two techniques in alopecia. Clin Exp Dermatol. 2011;36:855–63. doi: 10.1111/j.1365-2230.2011.04154.x. [DOI] [PubMed] [Google Scholar]
- 12.Miteva M. A comprehensive approach to hair pathology of horizontal sections. Am J Dermatopathol. 2013;35:529–40. doi: 10.1097/DAD.0b013e31826be7ba. [DOI] [PubMed] [Google Scholar]
- 13.Werner B, Mulinari-Brenner F. Clinical and histological challenge in the differential diagnosis of diffuse alopecia: Female androgenetic alopecia, telogen effluvium and alopecia areata-part I. An Bras Dermatol. 2012;87:742–7. doi: 10.1590/s0365-05962012000500012. [DOI] [PubMed] [Google Scholar]
- 14.Sinclair R, Jolley D, Mallari R, Magee J. The reliability of horizontally sectioned scalp biopsies in the diagnosis of chronic diffuse telogen hair loss in women. J Am Acad Dermatol. 2004;51:189–99. doi: 10.1016/s0190-9622(03)00045-8. [DOI] [PubMed] [Google Scholar]
- 15.Whiting DA. Histopathologic features of alopecia areata: A new look. Arch Dermatol. 2003;139:1555–9. doi: 10.1001/archderm.139.12.1555. [DOI] [PubMed] [Google Scholar]
- 16.Somani N, Bergfeld WF. Cicatricial alopecia: Classification and histopathology. Dermatol Ther. 2008;21:221–37. doi: 10.1111/j.1529-8019.2008.00203.x. [DOI] [PubMed] [Google Scholar]
- 17.Aslani FS, Dastgheib L, Banihashemi BM. Hair counts in scalp biopsy of males and females with androgenetic alopecia compared with normal subjects. J Cutan Pathol. 2009;36:734–9. doi: 10.1111/j.1600-0560.2008.01149.x. [DOI] [PubMed] [Google Scholar]
- 18.Knopp E. The scalp biopsy for hair loss and its interpretation. Semin Cutan Med Surg. 2015;34:57–66. doi: 10.12788/j.sder.2015.0144. [DOI] [PubMed] [Google Scholar]
- 19.Miteva M, Romanelli P, Tosti A. Pigmented casts. Am J Dermatopathol. 2014;36:58–63. doi: 10.1097/DAD.0b013e3182919ac7. [DOI] [PubMed] [Google Scholar]
- 20.Concha JSS, Werth VP. Alopecias in lupus erythematosus. Lupus Sci Med. 2018;5:e000291. doi: 10.1136/lupus-2018-000291. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Tandon YK, Somani N, Cevasco NC, Bergfeld WF. A histologic review of 27 patients with lichen planopilaris. J Am Acad Dermatol. 2008;59:91–8. doi: 10.1016/j.jaad.2008.03.007. [DOI] [PubMed] [Google Scholar]
- 22.Sperling LC. Premature desquamation of the inner root sheath is still a useful concept! J Cutan Pathol. 2007;34:809–10. doi: 10.1111/j.1600-0560.2006.00707.x. [DOI] [PubMed] [Google Scholar]
- 23.Sperling LC, Cowper SE. The histopathology of primary cicatricial alopecia. Semin Cutan Med Surg. 2006;25:41–50. doi: 10.1016/j.sder.2006.01.006. [DOI] [PubMed] [Google Scholar]
- 24.Stefanato CM. Histopathology of alopecia: A clinicopathological approach to diagnosis. Histopathology. 2010;56:24–38. doi: 10.1111/j.1365-2559.2009.03439.x. [DOI] [PubMed] [Google Scholar]
- 25.Bystryn JC, Orentreich N, Stengel F. Direct immunofluorescence studies in alopecia areata and male pattern alopecia. J Invest Dermatol. 1979;73:317–20. doi: 10.1111/1523-1747.ep12549703. [DOI] [PubMed] [Google Scholar]
- 26.Kolivras A, Thompson C. Primary scalp alopecia: New histopathological tools, new concepts and a practical guide to diagnosis. J Cutan Pathol. 2017;44:53–69. doi: 10.1111/cup.12822. [DOI] [PubMed] [Google Scholar]
Associated Data
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Supplementary Materials
Diagnostic algorithm for histopathological approach of alopecia