Abstract
Introduction
Distinguishing scarring (SA) versus non-scarring alopecia (NSA) may not be a simple procedure on either clinical or histopathological views.
Aims
We sought to study the interobserver variability in the histopathological assessment of SA versus NSA, including clinical-pathological considerations.
Methods
Two dermatopathologists independently interpreted the same set of 100 specimens (89 patients). The samples were serial sectioned and stained by hematoxylin and eosin and Verhöeff methods. The patients' mean age was 46 years, with 13 being males and 76 females.
Results
In 16/100 samples, there was no consensus among the two examiners regarding SA versus NSA (weighted kappa = 0.6583; 95% CI); 3/16 patients were re-biopsied, and in the second sample, consensus was reached. In 76/89 patients, the anatomopathological examination was helpful in defining the SA versus NSA subtype. Of the 84 samples in which there was interobserver agreement, 4 which had been considered scarring in the routine pathological report were re-classified as non-scarring, whereas one biopsy, previously diagnosed as non-scarring, was now considered cicatricial due to the newly found areas of lichenoid inflammation in the infundibular epithelium.
Discussion
The ideal scalp examination may require deep serial biopsy sectioning, elastic tissue stain, re-biopsy, and strict clinical-evolutive correlation.
Keywords: Alopecia, Scarring alopecia, Non-scarring alopecia, Scalp histopathology
Defining the Problem
Pathologists frequently receive scalp biopsies with presumptive clinical differential diagnoses, including scarring and non-scarring alopecias (SA vs. NSA), as fibrosing alopecia in a pattern distribution versus androgenetic alopecia [1]. This occurs because, from a clinical and trichoscopic point of view, it is not always easy to distinguish these two major groups of hair disorders [2]. The problem becomes even more complicated because it is not always simple to histopathologically differentiate scarring from non-scarring conditions [3]. A literature review shows that the morphological criteria used to differentiate the two groups of entities are not clearly determined, which is concerning due to the differences in their therapeutic approach and prognosis [2, 3]. The objective of this work was to explore the interobserver variability in the interpretation of scalp biopsies by two dermatopathologists, including clinical-pathological considerations.
Materials and Methods
This is a retrospective-analytical study. Data collection only took place after approval by the Institutional Research Ethics Committee (CAAE:15129119800005404). The registration numbers of all biopsies related to the term “alopecia” were extracted from the University of Campinas, Pathology Laboratory files from 2008 to 2018. Their respective clinical files were also obtained. Only patients with complete clinical histories and physical examinations, including trichoscopy, were included. A total of 100 specimens belonging to 89 patients were finally selected. All scalp samples were cut at serial levels and stained with hematoxylin and eosin and Verhoeff-van Gieson for elastic fibers. Two dermatopathologists blindly and independently examined the same set of specimens, and the evaluated variables are shown in Table 1 [4, 5, 6, 7, 8, 9, 10, 11, 12, 13] and Figures 1 and 2. The “arrector pili muscle pseudo-hyperplasia” variable was not described as an alopecia feature in the literature, but it was also recorded because it had been previously found in some specimens. The results were analyzed by the Biostatistics Division of the Medical Sciences School − UNICAMP (SAS System for Windows [Statistical Analysis System], version 9.4. SAS Institute Inc, 2002–2012, Cary, NC, USA). The patients' medical records were reviewed, and the following information was recorded: gender, age at the time of biopsy, family history, time of development of alopecia, extracephalic involvement, dermatological and trichoscopic examination of the scalp, traction test, evolution, blood test results, direct immunofluorescence of the scalp biopsy, if available, and clinical diagnosis.
Table 1.
Variables examined
| Variable | Method | |
|---|---|---|
| 1 | Elastic fibers | 0: intact; 1: clumped; 2: wedge-shaped absent elastin |
| with perifollicular fibrosis (LPP); 3: absent dermal elastin | ||
| with horizontal, interfollicular fibrosis (DLE) | ||
| 2 | Type of specimen embedding | 0: horizontal; 1: vertical; 2: both (2 samples) |
| 3 | Thickness of hypodermis (vertically embedded samples) | 0: absent or thin; 1: near the galea |
| 4 | Specimen size | In mm2 |
| 5 | Number of follicles in the sample | Total in the sample |
| 6 | Number of non-terminal follicles | Total in the sample |
| 7 | Number of miniaturized follicles | Total in the sample |
| 8 | Staggered follicular atrophy | 0: absent; 1: present |
| 9 | Number of non-anagen follicles | Total in the sample |
| 10 | Inflammatory infiltrate | 0: absent; 1: present, lymphocytic; 2: mixed |
| 11 | Topography of inflammatory infiltrate | 0: absent; 1: permanent portion; 2: cyclic portion |
| 12 | Lichenoid follicular damage | 0: absent; 1: present |
| 13 | Number of stelae in the hypodermis (vertically embedded samples) | Total in the sample |
| 14 | Number of stelae in the dermis (horizontally embedded samples) | Total in the sample |
| 15 | Trichomalacia | 0: absent; 1: present |
| 16 | Pigmented cast | 0: absent; 1: present |
| 17 | Fibrosis | 0: absent; 1: present; topography |
| 18 | Syringoma-like ductal proliferation/dilation | 0: absent; 1: present |
| 19 | Arrector pili muscle pseudo-hyperplasia | 0: absent; 1: present |
| 20 | Sebaceous glands | 0: normal; 1: fewer or absent |
| 21 | Naked hair shaft/giant cells | 0: absent; 1: present |
| 22 | Signs of lupus | 0: absent; 1: present |
| 23 | Epidermis: spongiosis/hyperplasia | 0: absent; 1: present |
| 24 | Alopecia subtype | 0: non-scarring; 1: scarring; 2: scarring and non-scarring |
| 25 | Histopathological diagnosis | 0: LPP group**; 1: LED; 2: AGA; 3: all other NSAs; 4: all |
| other SAs; 5: NS***; 6: AGA + associated subtype. | ||
| 26 | Observations |
LPP, lichen planopilaris; DLE, discoid lupus erythematosus; AGA, androgenetic alopecia.
NS, non-scarring.
Fig. 1.
Vertically sectioned scalp sample stained with Weigert van Gieson. a Lichen planus pilaris with wedge-shaped area of absent elastin (black arrows) and follicular replacement by fibrosis. b Discoid lupus erythematosus (late stage cicatricial alopecia) with scant residual dermal elastin (black arrows) and horizontal interfollicular fibrosis. On the right, residual sweat gland (yellow arrow). c SA, late stage, with localized follicular fibrosis (black arrow), clumped elastic fibers on the right and, focally, on the left. Original magnification, ×100.
Fig. 2.
a Arrector pili muscle pseudo-hyperplasia (arrows). b Alopecia areata with arrector pili muscle pseudo-hyperplasia (black arrows) and several germinal telogen units (blue arrows). c Syringoma-like ductal proliferation/dilation (arrows). d SA with naked hair shaft within giant cells (arrows). Hematoxylin and eosin stain. Original magnification ×40 (a–c) and ×400 (d).
Results
The age of patients ranged from 4 to 77 years (mean, 46 years), and the majority (N = 76) were female. In 16/100 biopsies, there was no consensus among the examiners regarding the subtype of alopecia (SA vs. NSA). The weighted kappa score was 0.6583 (95% confidence interval), and this result indicates good agreement among the two dermatopathologists. A new biopsy was obtained from 3 of these 16 patients, which resulted in consensus. The analysis of the remaining 13 samples (in which there was no consensus) revealed that there were findings shared by both forms of alopecia in the same specimen.
In 84 samples, there was perfect interobserver agreement; 4 considered as SA in the routine laboratory report (before the serial cuts and stains for elastic fibers) were re-classified as NSA, whereas one biopsy, previously diagnosed as NSA, was now considered cicatricial due to the newly found areas of lichenoid inflammation in the infundibular epithelium. Table 2 depicts clinical hypotheses and histopathological diagnoses in those 84 samples; 37 were classified as SA and 47 as NSA.
Table 2.
Clinical hypotheses in the 84 histopathological perfect interobserver agreement diagnoses
| Clinical hypotheses | Histopathological consensus diagnosis |
|
|---|---|---|
| SAa | NSAb | |
| SA (n = 29) | 28 | 1 |
| NSA (n = 32) | 0 | 32 |
| Non-scarring versus Scarring (n = 18) | 8 | 10 |
| Mixed alopeciaa (n = 4) | 2 | 2 |
| Mixed alopeciab (n = 1) | 1 | 1 |
| Total n = 84 | ||
Two sample cases, both samples with same diagnoses.
Two sample cases, each sample different diagnoses.
Of the 29 patients in whom the only clinical hypothesis was SA, 28 were classified as such by histopathology, and 1 patient, with a hypothesis of fibrosing frontal alopecia, was diagnosed with female pattern alopecia by using the same method. All 32 patients diagnosed clinically as having NSA were confirmed histologically.
Thirty-nine patients reported hair loss elsewhere in the integument. Of these, 20 were in the lichen planus pilaris group, out of a total of 26 diagnosed histologically; 2 patients had a histological diagnosis of alopecia areata, 6 of androgenetic alopecia, and 11 remaining patients had other forms of SA or NSA involving other body locations.
The descriptive statistical analysis of the histological findings obtained from the evaluation of the two observers regarding the arrangement of elastic fibers showed good interobserver agreement (kappa = 0.4660; 95% CI). The sample volume and orientation (vertical/horizontal) did not influence the result of the analysis of the reproducibility of elastic fibers or the alopecia subtype (p > 0.005).
Table 3 shows the histopathological variables that were predictive for one or another subtype of alopecia in those 84 cases where there was perfect interobserver agreement. The predictive factors to discriminate alopecia subtype (SA vs. NSA) proved to be aligned with those in the literature for the corresponding forms, confirming that they are reliable from a biological point of view (Table 3). On multiple analysis − stepwise process, the variables that, together, discriminated SA were density of non-terminal follicles − each unit diminished the chance of SA by 2 times (p = 0.0005; OR = 0.4999); absent/reduced sebaceous glands density: the chance of SA increased by approximately 59 times (p = 0.0015; OR = 58.939).
Table 3.
Results of univariate and multiple logistic regressions to discriminate alopecia subtype (1 scarring vs. 0 non-scarring)
| Histopathological variable | Subtype | p value | Odds ratio | 95% CI |
|---|---|---|---|---|
| Higher follicle density | NSA | 0.0005 | 0.804 | 0.711; 0.910 |
| Higher non-terminal follicles density | NSA | <0.0001 | 0.472 | 0.344; 0.648 |
| Higher miniaturized follicles density | NSA | <0.0001 | 0.259 | 0.102; 0.491 |
| Non-anagen follicles density | NSA | 0.0002 | 0.224 | 1.278; 2.475 |
| Stelae density in hypodermis | SA | 0.0006 | 1.779 | 1.278; 2.475 |
| Inflammation in follicular permanent portion | SA | 0.0003 | 6.028 | 2.300; 15.795 |
| Lichenoid infiltrate | SA | 0.0002 | 56.250 | 6.973; 453.785 |
| Syringoma-like ductal proliferation/dilation | SA | 0.0170 | 4.548 | 1.311; 15.774 |
| Pseudo-hyperplasia of arrector pilli muscle | SA | 0.0026 | 6.543 | 1.930; 22.188 |
| Lower sebaceous glands density | SA | <0.0001 | 35.997 | 9.228; 140.41 |
Mann-Whitney and Fisher's exact test.
Regarding the trichoscopic examination, the following findings correlated with (Mann-Whitney, χ2, and Fisher's exact tests, p < 0.05) (1) the scarring form of alopecia: perifollicular erythema; perifollicular desquamation; hyperkeratosis; hair casts; pili torti, and follicular plugs; (2) the non-scarring form of alopecia: variability in the diameter of the shaft and vellus hair. A direct correlation was found between hair regrowth and the non-scarring form of alopecia (χ2 test, p = 0.01).
Discussion
In general practice, clinical history, physical examination, and trichoscopic findings are helpful to identify the two main forms of alopecia (NSA and SA). In our cohort, 60/84 (71%) samples were sent for examination with only one diagnostic hypothesis (Table 2). As a result, the histopathological findings merely confirmed the proposed diagnosis (SA or NSA). However, the alopecia subtype may not be defined even after careful dermatological evaluation, necessitating a scalp biopsy. Indeed, among the 84 samples in which there was a consensus regarding the subtype of alopecia, in 18 cases (21%), the clinical proposed hypotheses were of both SA and NSA forms. Fortunately, in these samples, it was possible to define the alopecia subtype because, among many factors, they were evaluated by dermatopathologists under serial sections and special stains. However, we have to consider that the histological findings represent the substrate of the clinical picture. If it is not characteristic, the histological findings may not be conclusive. This may be one of the reasons for the interobserver disagreement in the 16 samples in this study. Some findings considered typical of a particular form of alopecia may not be constant in all diseases in the group. As an example, in NSA, the average volume of the sebaceous glands remains constant, but it may be reduced in alopecia areata [14] and psoriatic alopecia [15]. It is also important to remember that nosological processes are dynamic; the conditions that result in SA may resemble NSA in the early stages. Furthermore, the site from which the sample is obtained can also influence the histological result. Therefore, when the process follow-up is not consistent with the pathological report, the dermatologist should provide this information to the pathologist, and the following procedures could be followed. (1) Collect a new biopsy: effectively, in this cohort, in 3 of the 16 patients in whose biopsies there was no consensus among the observers, a new sample was obtained, and a consensus was achieved. Establishing a precise diagnosis for any group of alopecia can be challenging by itself [16, 17]. Twenty-nine out of 1,245 dermatopathology consultations sent to a web-based second opinion corresponded to difficult alopecia biopsies [18]. To make the diagnosis even more complicated, many patients have more than one form of alopecia [19, 20]. As an example, post-menopausal female patients who develop any form of alopecia commonly already have androgenetic alopecia. In addition, confounding factors add interpretation difficulties, such as young acne-prone patients developing any form of NSA, who may have foci of scalp folliculitis, cysts, and fibrosis. Therefore, the dermatopathologist must state the difficulties encountered in specimen interpretation in the pathological report (Fig. 3, 4). (2) Alternatively, proceed with additional sections of previously collected samples and use stains for elastic fibers [4, 5, 6, 7, 8]. In our series, this procedure allowed for the diagnosis alteration in 5 specimens. One of the specimens which had been reported as NSA demonstrated infundibular lichenoid inflammation in the new sections. This is an important issue, considering that SA should be treated as soon as possible because the hair follicles are permanently destroyed, leading to disfigurement and psychosocial embarrassment. Fast and safe diagnosis and aggressive treatment are crucial for therapeutic success, aiming to stop or delay the progression of hair loss and reduce the clinical signs of inflammation.
Fig. 3.
Example of a vertically sectioned scalp sample in which there was interobserver disagreement. a There is decreased density of hair follicles and sebaceous glands and two pseudo-hypertrophic arrector pili muscles (red arrows). Note three small intermediate follicles in the dermis (yellow arrows), a small terminal follicle in the hypodermis (black arrow), and an area outlined in blue of fibrosis or a collapsed perifollicular fibrous sheath (H&E). b On Weigert van Gieson stain, the elastic tissue around the region delimited in blue is dense but symmetrical. Original magnification, ×40 (a) and ×100 (b). Hematoxylin and eosin (a) and Weigert van Gieson (b) stain.
Fig. 4.
Another example of a scalp sample in which there was interobserver disagreement, this time in a transversal section specimen. a There is follicular rarefaction in several of the follicular units, but sebaceous glands are seen. There is variation in follicular diameter, some miniaturized (yellow arrows), other intermediate (red arrow), and other terminal (black arrow). Presence of follicular units (outlined in blue) with marked reduction in follicular density and apparent fibrosis (H&E). b On Weigert van Gieson method, in the regions outlined in blue, there is apparent fibrosis and absence of elastic fibers. Original magnification ×40 (a) and ×100 (b). Hematoxylin and eosin (a) and Weigert van Gieson (b) stain.
The predictive factors that discriminate alopecia subtype (SA vs. NSA) proved to be aligned with those in the literature for the corresponding forms, confirming that they are reliable from a biological point of view (Table 3). In the NSA, the density of follicles, miniaturized follicles, non-anagen phase follicles, and stelae in the dermis (horizontal inclusion) in the sample was higher. This occurs because the follicles decrease in volume or accelerate their cycle but are not destroyed. In the SA, in addition to the described characteristic findings, the early occurrence of atrophy of sebaceous glands proved to be a crucial criterion for SA [21]. In conclusion, the ideal scalp examination may require deep serial biopsy sectioning, elastic tissue stain, re-biopsy, and strict clinical-evolutive correlation.
Conclusion
When it is clinically difficult to differentiate an early SA from a non-scarring one, it is very important to know the histopathological details that support either of these hypotheses. In the case of discordance between pathologists, a new biopsy is a valuable option to reach the diagnosis.
Statement of Ethics
This study protocol was reviewed and approved by the Research Ethics Committee (CEP) of the State University of Campinas (Unicamp), which waived the need for informed consent. All the principles of the Declaration of Helsinki were observed (approval number: CAAE:15129119800005404).
Conflict of Interest Statement
The authors declare that they have no conflicts of interest, financial activities, or relationships to disclose, which might have influenced what is written in the submitted manuscript.
Funding Sources
FAPESP (São Paulo Research Foundation; #20/07199-0).
Author Contributions
Maria Leticia Cintra, Amanda Araujo dos Reis Botega, and Carolina Visa Amorim contributed to conceptualization and acquisition of funding; Maria Leticia Cintra, Amanda Araujo dos Reis Botega, Carolina Visa Amorim, and Cristina Diniz Borges Figueira de Mello contributed to methodology and interpretation of data; Fernanda Teixeira, Rafael Fantelli Stelini, and Paulo Eduardo Neves Ferreira Velho contributed to validation; Maria Leticia Cintra, Amanda Araujo dos Reis Botega, Cristina Diniz Borges Figueira de Mello, and Fernanda Teixeira contributed to formal analysis; Maria Leticia Cintra, Amanda Araujo dos Reis Botega, Rafael Fantelli Stelini, and Fernanda Teixeira contributed to investigation and data curation; Maria Leticia Cintra, Fernanda Teixeira, and Amanda Araujo dos Reis Botega contributed to writing of the manuscript and its review and editing. All authors have read and agreed to the published version of the manuscript.
Data Availability Statement
All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.
Acknowledgment
The present work was carried out with the support of the Coordination for the Improvement of Higher Education Personnel, Brazil (CAPES), Financing Code 001.
Funding Statement
FAPESP (São Paulo Research Foundation; #20/07199-0).
References
- 1.Griggs J, Trüeb RM, Gavazzoni Dias MFR, Hordinsky M, Tosti A. Fibrosing alopecia in a pattern distribution. J Am Acad Dermatol. 2021;85((6)):1557–64. doi: 10.1016/j.jaad.2019.12.056. [DOI] [PubMed] [Google Scholar]
- 2.Wu WY, Otberg N, McElwee KJ, Shapiro J. Diagnosis and management of primary cicatricial alopecia: Part II. Skinmed. 2008;7((2)):78–83. doi: 10.1111/j.1751-7125.2008.07586.x. [DOI] [PubMed] [Google Scholar]
- 3.Sperling LC. Scarring alopecia and the dermatopathologist. J Cutan Pathol. 2001;28((7)):333–342. doi: 10.1034/j.1600-0560.2001.280701.x. [DOI] [PubMed] [Google Scholar]
- 4.Tan T, Guitart J, Gerami P, Yazdan P. Elastic staining in differentiating between follicular streamers and follicular scars in horizontal scalp biopsy sections. Am J Dermatopathol. 2018;40((4)):254–258. doi: 10.1097/DAD.0000000000000973. [DOI] [PubMed] [Google Scholar]
- 5.Pinkus H. Differential patterns of elastic fibers in scarring and non-scarring alopecias. J Cutan Pathol. 1978;5((3)):93–104. doi: 10.1111/j.1600-0560.1978.tb00946.x. [DOI] [PubMed] [Google Scholar]
- 6.Fung MA, Sharon VR, Ratnarathorn M, Konia TH, Barr KL, Mirmirani P. Elastin staining patterns in primary cicatricial alopecia. J Am Acad Dermatol. 2013;69((5)):776–782. doi: 10.1016/j.jaad.2013.07.018. [DOI] [PubMed] [Google Scholar]
- 7.Ross EK, Tan E, Shapiro J. Update on primary cicatricial alopecias. J Am Acad Dermatol. 2005;53:1–37. doi: 10.1016/j.jaad.2004.06.015. [DOI] [PubMed] [Google Scholar]
- 8.Bolduc C, Sperling LC, Shapiro J. Primary cicatricial alopecia: lymphocytic primary cicatricial alopecias, including chronic cutaneous lupus erythematosus, lichen planopilaris, frontal fibrosing alopecia, and Graham-Little syndrome. J Am Acad Dermatol. 2016;75((6)):1081–99. doi: 10.1016/j.jaad.2014.09.058. [DOI] [PubMed] [Google Scholar]
- 9.Miteva M, Romanelli P, Tosti A. Pigmented casts. Am J Dermatopathol. 2014;36((1)):58–63. doi: 10.1097/DAD.0b013e3182919ac7. [DOI] [PubMed] [Google Scholar]
- 10.Du X, Li Z, Xu W, Zhou X, Tang S, Song C, et al. Diagnostic value of horizontal versus vertical sections for scarring and non-scarring alopecia: a systematic review and meta-analysis. Eur J Dermatol. 2016;26((4)):361–369. doi: 10.1684/ejd.2016.2797. [DOI] [PubMed] [Google Scholar]
- 11.Mehregan AH, Mehregan DA. Syringoma-like sweat duct proliferation in scalp alopecias. J Cutan Pathol. 1990;17((6)):355–357. doi: 10.1111/j.1600-0560.1990.tb00112.x. [DOI] [PubMed] [Google Scholar]
- 12.Chung HJ, Goldberg LJ. Histologic features of chronic cutaneous lupus erythematosus of the scalp using horizontal sectioning: emphasis on follicular findings. J Am Acad Dermatol. 2017;77((2)):349–355. doi: 10.1016/j.jaad.2017.02.039. [DOI] [PubMed] [Google Scholar]
- 13.Doytcheva K, Tan T, Guitart J, Gerami P, Yazdan P. Naked hair shafts as a marker of cicatricial alopecia. Am J Dermatopathol. 2018;40((7)):498–501. doi: 10.1097/DAD.0000000000001075. [DOI] [PubMed] [Google Scholar]
- 14.Pierard-Franchimont C, Pierard GE. Corroborative evidence that alopecia areata involves the epidermis and the sebaceous glands. Am J Dermatopathol. 1987;9((2)):111–113. doi: 10.1097/00000372-198704000-00005. [DOI] [PubMed] [Google Scholar]
- 15.Rittié L, Tejasvi T, Harms PW, Xing X, Nair RP, Gudjonsson JE, et al. Sebaceous gland atrophy in psoriasis: an explanation for psoriatic alopecia? J Invest Dermatol. 2016;136((9)):1792–800. doi: 10.1016/j.jid.2016.05.113. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Harries MJ, Trueb RM, Tosti A, Messenger AG, Chaudhry I, Whiting DA, et al. How not to get scar(r)ed: pointers to the correct diagnosis in patients with suspected primary cicatricial alopecia. Br J Dermatol. 2009;160((3)):482–501. doi: 10.1111/j.1365-2133.2008.09008.x. [DOI] [PubMed] [Google Scholar]
- 17.Kolivras A, Thompson C. Primary scalp alopecia: new histopathological tools, new concepts and a practical guide to diagnosis. J Cutan Pathol. 2017;44((1)):53–69. doi: 10.1111/cup.12822. [DOI] [PubMed] [Google Scholar]
- 18.Zembowicz A, Ahmad A, Lyle SR. A comprehensive analysis of a web-based dermatopathology second opinion consultation practice. Arch Pathol Lab Med. 2011;135((3)):379–383. doi: 10.5858/2010-0187-OA.1. [DOI] [PubMed] [Google Scholar]
- 19.Wohltmann WE, Sperling L. Histopathologic diagnosis of multifactorial alopecia. J Cutan Pathol. 2016;43((6)):483–491. doi: 10.1111/cup.12698. [DOI] [PubMed] [Google Scholar]
- 20.Fukuyama M, Ohyama M. Use of trichoscopy for the diagnosis of alopecia areata coexisting with primary scarring alopecia in a female hair loss patient. J Dermatol. 2019;46((5)):418–421. doi: 10.1111/1346-8138.14841. [DOI] [PubMed] [Google Scholar]
- 21.McElwee KJ. Etiology of cicatricial alopecias: a basic science point of view. Dermatol Ther. 2008;21((4)):212–220. doi: 10.1111/j.1529-8019.2008.00202.x. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.