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Background: There is considerable variation in the literature regarding the dermatopathologic diagnostic features of and reporting guidelines for actinic keratosis (AK) and cutaneous squamous cell carcinoma (cSCC)., Objective: To develop consensus recommendations regarding diagnostic criteria, nomenclature, and reporting of AK and cSCC., Methods: Literature review and cross-sectional multiround Delphi process including an international group of expert dermatopathologists followed by a consensus meeting., Results: Consensus was achieved regarding the key dermatopathologic features necessary for diagnosing cSCC, AK, and associated variants; grading of degree of cellular differentiation in cSCC; utility of immunohistochemistry for diagnosis of cSCC; and pathologic features that should be reported for cSCC and AK., Limitations: Consensus was not achieved on all questions considered., Conclusion: Despite the lack of clarity in the literature, there is consensus among expert dermatopathologists regarding diagnostic criteria and appropriate reporting of AK and cSCC. Widespread implementation of these consensus recommendations may improve communication between dermatopathologists and clinicians, facilitating appropriate treatment of AK and cSCC., Competing Interests: Conflicts of interest None disclosed., (Copyright © 2023 American Academy of Dermatology, Inc. Published by Elsevier Inc. All rights reserved.)

Competing Interests: None disclosed.

Background: Appropriate use criteria (AUC) provide patient-centered physician guidance in test selection. An initial set of AUC was reported by the American Society of Dermatopathology (ASDP) in 2018. AUC reflect evidence collected at single timepoints and may be affected by evolving evidence and experience. The objective of this study was to update and expand AUC for selected tests., Methods: RAND/UCLA (RAND Corporation [Santa Monica, CA]/University of California Los Angeles) methodology used includes the following: (a) literature review; (b) review of previously rated tests and previously employed clinical scenarios; (c) selection of previously rated tests for new ratings; (d) development of new clinical scenarios; (e) selection of additional tests; (f) three rating rounds with feedback and group discussion after rounds 1 and 2., Results: For 220 clinical scenarios comprising lymphoproliferative (light chain clonality), melanocytic (comparative genomic hybridization, fluorescence in situ hybridization, reverse transcription polymerase chain reaction, telomerase reverse transcriptase promoter), vascular disorders (MYC), and inflammatory dermatoses (periodic acid-Schiff, Gömöri methenamine silver), consensus by panel raters was reached in 172 of 220 (78%) scenarios, with 103 of 148 (70%) rated "usually appropriate" or "rarely appropriate" and 45 of 148 (30%), "appropriateness uncertain.", Limitations: The study design only measures appropriateness. Cost, availability, test comparison, and additional clinical considerations are not measured. The possibility that the findings of this study may be influenced by the inherent biases of the dermatopathologists involved in the study cannot be excluded., Conclusions: AUC are reported for selected diagnostic tests in clinical scenarios that occur in dermatopathology practice. Adhering to AUC may reduce inappropriate test utilization and improve healthcare delivery., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Immunohistochemistry for preferentially expressed antigen in melanoma (PRAME) has been studied in melanocytic lesions but not nonmelanoma skin cancers (NMSCs). This study evaluated PRAME expression in NMSCs and dermoepidermal junction (DEJ) melanocytes in the surrounding skin., Methods: Ninety-nine NMSCs were studied: 23 Merkel cell carcinomas (MCCs), 25 well to poorly differentiated squamous cell carcinomas (SCCs), 14 basal cell carcinomas (BCCs), five basosquamous carcinomas, four sebaceous carcinomas, ten atypical fibroxanthomas, 11 dermatofibrosarcoma protuberans, and seven leiomyosarcomas. Staining quality was considered low or high intensity. Staining quantity was reported as negative 0%, 1% to 24%, 25% to 50%, and >50%. DEJ melanocyte PRAME expression was recorded., Results: Forty-eight percent of NMSCs showed PRAME expression, mostly low intensity in fewer than 25% of cells. High-intensity expression was noted in one poorly differentiated SCC, six BCCs, and seven MCCs. Only MCCs showed expression in greater than 25% of tumor cells. Focal DEJ melanocytes expressed high-intensity PRAME in 18% of cases, most commonly SCCs (11/23)., Conclusions: PRAME is negative or expressed with low intensity in a small percentage of NMSCs, with the exception of some MCC showing high-intensity and diffuse staining. Focal DEJ melanocytes showed high-intensity PRAME reactivity in the skin surrounding some NMSCs., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Accurate prognostic biomarkers in early-stage melanoma are urgently needed to stratify patients for clinical trials of adjuvant therapy. We applied a previously developed open source deep learning algorithm to detect tumor-infiltrating lymphocytes (TILs) in hematoxylin and eosin (H&E) images of early-stage melanomas. We tested whether automated digital (TIL) analysis (ADTA) improved accuracy of prediction of disease specific survival (DSS) based on current pathology standards. ADTA was applied to a training cohort (n = 80) and a cutoff value was defined based on a Receiver Operating Curve. ADTA was then applied to a validation cohort (n = 145) and the previously determined cutoff value was used to stratify high and low risk patients, as demonstrated by Kaplan-Meier analysis (p ≤ 0.001). Multivariable Cox proportional hazards analysis was performed using ADTA, depth, and ulceration as co-variables and showed that ADTA contributed to DSS prediction (HR: 4.18, CI 1.51-11.58, p = 0.006). ADTA provides an effective and attainable assessment of TILs and should be further evaluated in larger studies for inclusion in staging algorithms.

The American Society of Dermatopathology has established an Appropriate Use Criteria (AUC) Committee with the intention of establishing evidence-based recommendations regarding the appropriateness of various ancillary tests commonly utilized by dermatopathologists. Periodic acid Schiff (PAS) and Grocott (or Gomori) methenamine silver (GMS) stains represent some of the most commonly employed ancillary tests in dermatopathology. The utility of these tests was targeted for evaluation by the AUC. This literature review represents a comprehensive evaluation of available evidence for the utility of PAS and/or GMS staining of skin and nail biopsies. In concert with expert opinion, these data will be incorporated into future recommendations by the AUC for PAS and GMS staining in routine dermatopathology practice., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: Biomarkers for disease-specific survival (DSS) in early-stage melanoma are needed to select patients for adjuvant immunotherapy and accelerate clinical trial design. We present a pathology-based computational method using a deep neural network architecture for DSS prediction., Experimental Design: The model was trained on 108 patients from four institutions and tested on 104 patients from Yale School of Medicine (YSM, New Haven, CT). A receiver operating characteristic (ROC) curve was generated on the basis of vote aggregation of individual image sequences, an optimized cutoff was selected, and the computational model was tested on a third independent population of 51 patients from Geisinger Health Systems (GHS)., Results: Area under the curve (AUC) in the YSM patients was 0.905 ( P < 0.0001). AUC in the GHS patients was 0.880 ( P < 0.0001). Using the cutoff selected in the YSM cohort, the computational model predicted DSS in the GHS cohort based on Kaplan-Meier (KM) analysis ( P < 0.0001)., Conclusions: The novel method presented is applicable to digital images, obviating the need for sample shipment and manipulation and representing a practical advance over current genetic and IHC-based methods., (©2019 American Association for Cancer Research.)

Background: Muir-Torre syndrome (MTS) is a rare inherited syndrome, with an increased risk of sebaceous and visceral malignancy. Prior reports suggest screening for mismatch repair (MMR) deficiency may be warranted in patients <50 years and when sebaceous neoplasms are located on a non-head and neck location. Previously, appropriate use criteria (AUC) were developed for clinical scenarios in patients >60 years concerning the use of MMR protein immunohistochemistry (MMRP-IHC). This analysis explores the appropriateness of testing in patients ≤60 years., Methods: Panel raters from the AUC Task Force rated the use of MMRP-IHC testing for MTS for previously rated scenarios with the only difference being age., Results: Results verify the previously developed AUC for the use of MMRP-IHC in neoplasms associated with MTS in patients >60 years. Results also show that in patients ≤60 years with a single sebaceous tumor on a non-head and neck site, MMRP-IHC testing should be considered. Testing can also be considered with a 2-antibody panel on periocular sebaceous carcinoma in younger patients., Conclusions: Our findings align with known evidence supporting the need to incorporate clinical parameters in identifying patients at risk for MTS, with age being a factor when considering MMRP-IHC testing., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Appropriate use criteria (AUC) provide physicians guidance in test selection, and can affect health care delivery, reimbursement policy, and physician decision-making., Objectives: The American Society of Dermatopathology, with input from the American Academy of Dermatology and the College of American Pathologists, sought to develop AUC in dermatopathology., Methods: The RAND/UCLA appropriateness methodology, which combines evidence-based medicine, clinical experience, and expert judgment, was used to develop AUC in dermatopathology., Results: With the number of ratings predetermined at 3, AUC were developed for 211 clinical scenarios involving 12 ancillary studies. Consensus was reached for 188 (89%) clinical scenarios, with 93 (44%) considered "usually appropriate" and 52 (25%) "rarely appropriate" and 43 (20%) having "uncertain appropriateness.", Limitations: The methodology requires a focus on appropriateness without comparison between tests and irrespective of cost., Conclusions: The ultimate decision to order specific tests rests with the physician and is one where the expected benefit exceeds the negative consequences. This publication outlines the recommendations of appropriateness-the AUC for 12 tests used in dermatopathology. Importantly, these recommendations may change considering new evidence. Results deemed "uncertain appropriateness" and where consensus was not reached may benefit from further research., (Copyright © 2018 American Academy of Dermatology, Inc. Published by Elsevier Inc. All rights reserved.)

Background: Appropriate use criteria (AUC) provide physicians guidance in test selection, and can affect health care delivery, reimbursement policy and physician decision-making., Objectives: The American Society of Dermatopathology, with input from the American Academy of Dermatology and the College of American Pathologists, sought to develop AUC in dermatopathology., Methods: The RAND/UCLA appropriateness methodology, which combines evidence-based medicine, clinical experience and expert judgment, was used to develop AUC in dermatopathology., Results: With the number of ratings predetermined at 3, AUC were developed for 211 clinical scenarios involving 12 ancillary studies. Consensus was reached for 188 (89%) clinical scenarios, with 93 (44%) considered "usually appropriate," 52 (25%) "rarely appropriate" and 43 (20%) "uncertain appropriateness.", Limitations: The methodology requires a focus on appropriateness without comparison between tests and irrespective of cost., Conclusions: The ultimate decision of when to order specific test rests with the physician and is one where the expected benefit exceeds the negative consequences. This publication outlines the recommendations of appropriateness-AUC for 12 tests used in dermatopathology. Importantly, these recommendations may change considering new evidence. Results deemed "uncertain appropriateness" and where consensus was not reached may benefit from further research., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Molecular technologies offer clinicians the tools to provide high-quality, cost-effective patient care. We evaluated education focused on molecular diagnostics, genomics, and personalized medicine in dermatopathology fellowship training., Design: A 20-question online survey was emailed to all (n = 53) Accreditation Council for Graduate Medical Education (ACGME)-accredited dermatopathology training programs in the United States., Results: Thirty-one of 53 program directors responded (response rate = 58%). Molecular training is undertaken in 74% of responding dermatopathology fellowships, with levels of instruction varying among dermatology-based and pathology-based programs. Education differed for dermatology- and pathology-trained fellows in approximately one-fifth (19%) of programs. Almost half (48%) of responding program directors believe that fellows are not currently receiving adequate molecular education, although the majority (97%) expect to incorporate additional instruction in the next 2-5 years. Factors influencing the incorporation of relevant education include perceived clinical utility and Accreditation Council for Graduate Medical Education/residency review committee (RRC) requirements. Potential benefits of molecular education include increased medical knowledge, improved patient care, and promotion of effective communication with other healthcare professionals. More than two-thirds (68%) of responding program directors believe that instruction in molecular technologies should be required in dermatopathology fellowship training., Conclusions: Although all responding dermatopathology fellowship program directors agreed that molecular education is important, only a little over half of survey participants believe that their fellows receive adequate instruction. This represents an important educational gap. Discussion among those who oversee fellow education is necessary to best integrate and evaluate teaching of molecular dermatopathology.

Introduction: Ulcerated melanomas may have a unique biology and microenvironment. We test whether markers of immune infiltration correlate with clinical outcome in ulcerated compared to non-ulcerated primary melanoma tumors., Methods: Sixty-two stage II-III cutaneous melanomas, 32 ulcerated and 30 non-ulcerated, were analyzed for tumor-infiltrating lymphocytes (TILs). Immunohistochemistry (IHC) was performed for CD2, a marker previously shown to correlate with overall survival (OS) and recurrence-free survival (RFS) in this patient population. IHC using antibody, VE1, to BRAF V600E was also performed on a subset of 41 tumors to assess the relationship of BRAF mutation to immune markers., Results: We found, using Cox regression models, that the presence of TILs was associated with improved OS (p = 0.034) and RFS (p = 0.002) in ulcerated melanoma tumors, but not in non-ulcerated melanoma (p = 0.632, 0.416). CD2 expression also was correlated with improved OS (p = 0.021) and RFS (p = 0.001) in ulcerated melanoma, but no relationship was seen in non-ulcerated melanoma (p = 0.427, 0.682). In this small population, BRAF status did not correlate with TILs or CD2+ count., Conclusion: Our data show that immune markers including TILs and CD2 count correlate more closely with survival in ulcerated melanomas than that in non-ulcerated melanomas. We propose that immune biomarkers may be particularly relevant to ulcerated, as compared to non-ulcerated, melanomas and that this merits study in larger populations.

Context: Immunohistochemistry is not a diagnostic test but a highly valuable tool that requires interpretation within a context., Objective: To review the current status and limitations of immunohistochemistry in dermatopathology., Data Sources: English-language literature published between 1980 and 2014., Conclusions: Although immunohistochemistry is rarely completely specific or sensitive, it is an important adjunctive technique in dermatopathology and can be helpful in a series of diagnostic dilemmas.

Metastasis from malignant melanoma (MM) usually first presents in the draining lymph node basin and thus sentinel lymph node (SLN) biopsy is a staging tool used to predict risk of metastases and death in higher risk tumors and has become the standard of care. Differences in the processing and methods used in the histopathological examination of SLNs can affect the positivity rate for metastatic MM because isolated MM deposits may be small and variably distributed in the SLN. The examination of SLNs is not standardized. The authors surveyed institutions across the United States who process SLNs for MM to better characterize the current methods used and to suggest a standardized approach to improve the reliability of the SLN biopsy. A survey of 142 academic institutions in the United States regarding the methods used in the evaluation of the SLN biopsy for MM was conducted. Thirty-two institutions responded. Eighty-one percent of the institutions (26 of 32) had a protocol that they used for SLN examination. In regards to gross dissection, 28% of the responders (9 of 32) initially bivalve (cut the SLN in half), whereas 59% (19 of 32) use a bread loaf technique, cutting the SLN at even intervals without specifically commenting about orientation to the hilum. The number of levels initially cut from the SLN block varied from 1 to 8 levels per block. Thirty-nine percent of the respondents (12 of 31) routinely order immunohistochemistry before evaluation of the initial hematoxylin- and eosin-stained sections. Eighty percent of the respondents (24 of 30) report the maximum dimension of the metastatic tumor deposit. The response rate was low (22%), and most respondents did not indicate how many SLN accessions were performed at their institution each year. Histologic protocols for processing SLNs for MM vary among institutions. Different methods of handling SLNs result in varying sensitivities for detection of metastases. Data derived from these varied approaches to develop and determine prognostic and staging categories may be inconsistent. A standardized yet practical approach is needed to provide reliable information on which prognosis can be determined and therapeutic guidelines can be based. The hope is for dermatologists and those treating patients with MM to understand the intricacies and inconsistencies involved in performance and interpretation of this key staging tool.

This article is an up-to-date overview of the potential uses and limitations of immunohistochemistry (IHC) in melanocytic lesions. The information is intended to assist dermatopathologists and dermatologists who read slides to appropriately use IHC in this setting. In addition, dermatologists who do not review microscopic slides will better understand the rationale of the pathologist when reading and interpreting the pathology report., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Early diagnosis of mycosis fungoides (MF) is one of the most challenging problems in dermatopathology, as the histopathologic features of inflammatory dermatoses and MF may show significant overlap. One criterion used to distinguish early MF (patch stage) from dermatitis, which may be currently underutilized, is the presence of eosinophils. A search was performed for cases with a preoperative diagnosis of MF, cutaneous T-cell lymphoma, or dermatitis, which included 29 cases "diagnostic" for MF, 25 cases "suspicious" for MF, and 55 cases of spongiotic dermatitis. We examined tissue sections blinded to diagnosis to obtain an exact eosinophil count. Twenty-nine cases were diagnostic for MF (12 patch, 9 plaque, and 8 tumor stage). The average eosinophil count for cases diagnostic for patch stage MF was 1 eosinophil in 10 (0.11) sections examined. For plaque MF, there was 1 eosinophil in 5 (0.24) sections examined. All tumor stage MF cases showed abundant eosinophils within each section. Twenty-five cases were suspicious for MF (15 patches, 9 plaques, and 1 folliculotropic). The average eosinophil count for the patch lesions was 1 eosinophil in 4 (0.25) sections examined and 2 eosinophils per section for plaque lesions. Forty-five of 55 cases of spongiotic dermatitis had at least scattered eosinophils (>3) in each section. Twenty-three (47%) had eosinophils around most postcapillary venules. Only 3 of 45 patients (6.6%) with biopsies diagnostic or suspicious for patch or plaque stage MF showed >3 eosinophils per tissue section, whereas 45 of 55 (81.8%) biopsies of spongiotic dermatitis had >3. The presence of eosinophils (>3 per tissue section) is statistically significant in differentiating cases diagnostic or suspicious for patch or plaque stage MF from dermatitis (P < 0.0001). Our data indicate that eosinophils are uncommon in cases of patch and plaque MF. When a pathologist is faced with evaluating a biopsy that lacks some of the criteria used to make the diagnosis of patch stage MF, yet demonstrates >3 eosinophils per tissue section, dermatitis is the likely diagnosis. However, in cases where fewer than 3 eosinophils are present in sections, patch stage MF cannot be excluded.

Chronic lymphocytic leukemia (CLL) is a common hematologic malignancy associated with an increased risk of non-melanoma skin cancer. Basal cell carcinomas and squamous cell carcinomas in these patients may have an associated dense peritumoral leukemic infiltrate. This infiltrate can lead to the diagnosis of CLL and may also obscure tumor margins and pose a challenge in the assessment of perineural tumor spread. Immunohistochemical stains are useful in distinguishing leukemic B-cell infiltrates from tumor-reactive T-cell infiltrates. Leukemic cells of CLL are CD20+/CD23+/CD5+/CD43+/CD3-, whereas benign reactive infiltrates are composed of CD20-/CD23-/CD5+/CD43+/CD3+ T-cells. Given the paucity of symptoms in early stages of CLL, a dense lymphoid infiltrate surrounding a cutaneous neoplasm may serve as the first indication of CLL. We report a series of three cases of SCC with a coexisting infiltrate of CLL, including one with perineural involvement, one involving metastatic SCC, and one in which this histologic finding spurred the initial diagnosis of CLL.

The sentinel lymph node from a 72-year-old female with melanoma revealed a pigmented and spindled melanocytic proliferation in the capsule that extended into the trabeculae. Benign nodal nevi are uncommon but have been reported in lymph nodes of melanoma patients and less often in lymph nodes removed for other reasons. Nodal blue nevi are particularly rare. These melanocytic proliferations can be distinguished from metastatic melanoma by evaluation of the distribution in the node, morphologic characteristics and the assistance of immunohistochemistry., (Copyright © 2009 John Wiley & Sons A/S.)

Zoonoses are infectious diseases that can be transmitted from animals to humans. Transmission occurs directly or through vectors such as ticks, mosquitoes, or flies. The causative agents include bacteria, parasites, viruses, and fungi. Domestic pets and livestock, as well as wild animals, can be the source of disease. In this summary, we will focus on a number of dermatologically relevant examples.

We report two cases of hydroxychloroquine-induced hyperpigmentation presenting in a 50-year-old Caucasian female (case 1) and a 78-year-old female (case 2), both receiving 400 mg per day. Case 1 had an arthritis predominant undifferentiated connective tissue disease, which was treated with hydroxychloroquine for 4-5 years. She presented with a mottled, reticulated macular gray pigmentation involving the upper back and shoulders. Case 2 had a history of systemic lupus erythematosus and rheumatoid arthritis, treated with hydroxychloroquine for 1.5 years. She presented to the hospital for treatment of constrictive cardiomyopathy and was noted to have a blue macular pigmentation involving the right temple. The biopsies from both patients showed superficial dermal, yellow-brown, non-refractile and coarsely granular pigment deposition. A Fontana-Masson stain highlighted some of these granules, while the Perl's iron stain was negative. Rare, previous reports of hyperpigmentation indicate the presence of both melanin and hemosiderin in patients being treated with antimalarial medication. To our knowledge, this staining pattern for hydroxychloroquine has not been previously reported in the literature and supports that hydroxychloroquine, in addition to chloroquine, binds to melanin.

Body piercing is a growing trend, especially in young people, but the literature on complications of piercing consists mostly of case reports involving ear piercing. Previous reported complications of piercing include contact dermatitis, keloids, traumatic tearing, viral transmission, and bacterial infections. We report two patients who presented with atypical mycobacterial infections of body piercing sites. It is important to recognize the association of piercing and mycobacterial infections so that tissue can be obtained for histopathologic examination and appropriate culture.

Background: Major pathology textbooks suggest that the shape of the vessel and the presence or absence of an internal elastic lamina are the best means to distinguish an artery from a vein. Because the shape of the vessel is highly dependent upon the plane of section, the internal elastic lamina is often cited as a more reliable criterion. After evaluating a patient with superficial thrombophlebitis, in whom these conventional criteria had led to a misdiagnosis of polyarteritis nodosa, we sought to determine whether the pattern of smooth muscle in the media is a more sensitive discriminator between an artery and a vein., Methods: Anatomically identified arteries and veins were harvested from extremity amputation specimens and stored autopsy organ specimens and reviewed by two dermatopathologists who were blinded to the gross pathologist's impression. The biopsies were assessed for the smooth muscle pattern and the presence or absence of an internal elastic lamina., Results: Forty-seven of the 50 cases (94%) were concordant with the pathologist's gross impression using only the smooth muscle pattern to differentiate an artery from a vein. On the basis of the presence or absence of an internal elastic lamina, 41 of 50 cases (82%) were concordant with the prosector's designation of the vessel., Limitations: Vessels were harvested from a variety of sites, with lower extremity vessels predominating. There may be some regional variability not addressed in this study., Conclusion: In this study, the pattern of muscle fibers within the vascular media discriminated between arteries and veins better than assessment of the presence or absence of an internal elastic lamina. Although no single criterion is 100% reliable, assessment of both these criteria may minimize the risk of misinterpreting vessels in the deep dermis and subcutis.

Proliferations of Langerhans cells can be histologically divided into cytologically benign Langerhans cell proliferations, which include the clinical syndromes of Langerhans cell histiocytosis, and cytologically malignant Langerhans cell sarcoma. We report a Langerhans cell sarcoma in a 33-year-old male that arose on the posterior thigh with subsequent regional lymph node involvement. Conventional microscopic, immunohistochemical, and ultrastructural analysis confirmed Langerhans cell differentiation. Aberrant CD31 expression, similar to that described previously in Langerhans cell histiocytosis, was prominent in this tumor, possibly enhancing its migratory capabilities.

Background: Both vertical and transverse sections are used in the histologic interpretation of alopecia biopsy specimens. Although a combination of the two may be optimal, the pathologist is frequently only provided with a single specimen. Even though the trend in recent years has been toward transverse sections in this setting, we are not aware of any published data directly comparing the two methods., Methods: One hundred two consecutive archived hair biopsy accessions that demonstrated comparable vertical and transverse sections were examined twice, each time in a random order. The pathologist's interpretation based only on the vertical sections and an interpretation based only on the transverse sections were compared with the original biopsy report, which had been based on the combination of vertical and transverse sections., Results: In 76 cases, all 3 diagnoses were concordant (ie, the diagnosis made with vertical sections alone, the diagnosis made with transverse sections alone, and the original diagnosis were all in agreement). In 2 cases, neither the diagnosis made with vertical sections alone nor the diagnosis made with transverse sections alone were in full agreement with the original diagnosis. In 20 cases, only the diagnosis made with vertical sections was concordant with the original diagnosis. In 4 cases, only the diagnosis made with transverse sections alone was concordant with the original diagnosis., Limitations: Our practice is heavily weighted toward scarring alopecia, and the results of our study may not be applicable to practices weighted toward other forms of alopecia. Because the cases had been signed out over a period of several years, the nomenclature for some entities changed. For the purposes of our study, we counted the diagnoses of follicular degeneration syndrome and idiopathic pseudopelade to be subtypes of (and concordant with) a diagnosis of central centrifugal cicatricial alopecia. In some cases, a definitive diagnosis was not possible at the time of the original diagnosis, but rather the pathologist had provided a histologic description and a differential diagnosis. For purposes of this study, an interpretation was considered to be concordant with the original descriptive diagnosis if all of the important histologic features were identified that had been described in the original report. Sampling error could have contributed to discordant diagnoses, but would be expected to affect both vertical and transverse samples in a random manner., Conclusion: The combination of vertical and transverse sections is superior to either alone. Although transverse sections have revolutionized the evaluation of alopecia, in this study, the diagnosis made with vertical sections alone had a higher concordance rate with the combination than did transverse sections alone. As there are advantages and disadvantages inherent in either method, when only a single biopsy specimen is submitted, it may be sectioned either vertically or transversely, at the discretion of the pathologist. With either method, serial step sections should be obtained to reduce the risk of missing important histologic findings.