Transverse sectioning in the evaluation of skin biopsy specimens from alopecic dogs.

R Bond,J Patterson‐Kane,K Stevens,H W Brooks Brownlie,A Hendricks

doi:10.1111/jsap.13243

R Bond, J Patterson‐Kane + Show 3 more

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https://doi.org/10.1111/jsap.13243

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Abstract

Transverse sectioning of skin biopsy specimens has revolutionised assessment of human alopecia by demonstration of every hair in each specimen, allowing quantitative evaluation of follicular activity. Since only vertical sectioning is performed routinely in veterinary laboratories, we aimed to determine whether transverse sectioning was a valuable technique in assessment of canine alopecia. Paired vertical and transverse sections of biopsy specimens from 31 alopecic dogs were examined independently in triplicate in random order and blinded to previous diagnosis using a standard check-list proforma. Assessments of key features (follicular activity [anagen/telogen], infundibular hyperkeratosis, sebaceous gland abnormalities, pigment clumping, dermal inflammation) by each sectioning method were compared. In the 31 cases, (atrophic [n=13], dysplastic [n=12], inflammatory diseases [n=6]), follicular inactivity scores (median, [lower-upper quartile]) in transverse sections significantly exceeded those in vertical sections (transverse 4 [3-5], vertical 3 [2-4]). Agreement between the two sectioning planes was moderate for infundibular hyperkeratosis (kappa=0.5210) and dermal inflammation (0.4351), fair for sebaceous gland abnormalities (0.3966) and pigment clumping (0.2197), but slight for follicular activity (0.1041). Vertical sectioning demonstrated diagnostically important epidermal pathology (n=2) and dermal thinning (n=3) whereas transverse sectioning enhanced assessment of hair growth phase (n=11), follicular structure and architecture (n=11), and focal luminal or mural folliculitides (n=3). Transverse sectioning confers significant benefits and complements traditional vertical sectioning in the histological assessment of canine hair follicle diseases, particularly when subtle abnormalities comprise distorted compound follicle architecture, hair cycle arrest or when relatively few adnexal structures are affected.

Highlights

The histopathological examination of skin biopsy specimens is an important tool in the diagnosis of alopecia in dogs when associated with atrophic, dysplastic and mural hair follicle diseases (Gross et al 2005)
It is normal practice for skin biopsy specimens to be sectioned vertically, demonstrating changes in the full thickness of the skin from epidermis to subcutaneous fat (Dunstan 1990). This is not without limitations; only a few hair follicles are present in each section and slight deviations from the optimal plane of sectioning result in hair follicle segments at different levels that can be difficult to orient
Examination of sections taken at different levels of the block allows anagen – telogen ratios and other abnormalities to be quantified, and the same hair follicle studied at different levels

Summary

Introduction

The histopathological examination of skin biopsy specimens is an important tool in the diagnosis of alopecia in dogs when associated with atrophic, dysplastic and mural hair follicle diseases (Gross et al 2005). It is normal practice for skin biopsy specimens to be sectioned vertically, demonstrating changes in the full thickness of the skin from epidermis to subcutaneous fat (Dunstan 1990). This is not without limitations; only a few hair follicles are present in each section and slight deviations from the optimal plane of sectioning result in hair follicle segments at different levels that can be difficult to orient. Examination of sections taken at different levels of the block allows anagen – telogen ratios and other abnormalities to be quantified, and the same hair follicle studied at different levels Such follicular counts are valuable in the diagnosis and treatment of non-cicatricial alopecia (Whiting 2008). A recent consensus statement from a group of experts in the field of cicatricial alopecia of humans acknowledged that the combined transverse and vertical sectioning of biopsy specimens was optimal but suggested that in cases where only a single biopsy was available, sections should be transverse (Olsen et al 2003)

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