Aprile 2022 - N° 49
Giornale Italiano di Tricologia
Histopathology of alopecia
“The learning and the knowledge that we have, is, at the most, but little compared with that of which we are ignorant“ Plato (The Republic)
A clinicopathological approach to diagnosis REVIEW (Histopathology 2010, 56, 24-38) Catherine M Stefanato Department of Dermatopathology, St John’s Institute of Dermatology, St Thomas’Hospital, London, UK
Introduction
Summary
Primary alopecia of the scalp is commonly divided into two groups, namely scarring and non-scarring. The histopathological interpretation of scalp biopsy specimens of patients with alopecia, whether scarring or non-scarring, may represent a challenging task, especially in the absence of a good, definitive clinical history, adequate tissue sampling, and an appropriate grossing technique. The histopathology of the most commonly encountered varieties of primary scarring (cicatricial) and nonscarring alopecias forms the basis of this review.
Interpretation of the histopathological findings of primary scarring and non-scarring alopecias may prove daunting. This is especially true if the biopsy specimen is inadequate, and the clinical history and pattern of the alopecia are not known. Common forms of scarring alopecias discussed here are the lymphocytic (discoid lupus erythematosus, lichen planopilaris, central centrifugal cicatricial alopecia, pseudopelade of Brocq), the neutrophilic (folliculitis decalvans, dissect ing folliculitis), and the mixed (acne keloidalis) entities. The non-scarring alopecias reviewed are androgenic alopecia, telogen effluvium, alopecia areata, trichotil lomania and traction alopecia. In all cases of primary alopecia, adequate tissue sampling laboratory processing, in combination with pertinent clinical information, provide the key to diagnosis.
Grossing technique considerations The current gold-standard for a scalp biopsy specimen is the use of a 4-mm punch; the specimen may be sectioned vertically or transversely. VERTICAL (longitudinal) SECTIONS
Keywords: Keywords clinicopathological correlation, histopathology, non-scarring alopecia, scarring alopecia
A 4-mm vertically-sectioned punch biopsy specimen is adequate for assessing alopecias associated with interface changes, lichenoid infiltrates, and subcutaneous pathology 1. However, only portions of a small number of follicular units (2–3) are seen in a given tissue section 2, because the hair follicles, which grow at an angle, are cut tangentially and, as such, cannot be visualized in their entirety in con-
Abbreviations: Abbreviations AA, alopecia areata; CCCA, central centrifugal cicatricial alopecia; H&E, haematoxylin and eosin; LPP, lichen planopilaris; PAS, periodic acid-Schiff; SLE, systemic lupus erythematosus; T, terminal; V, vellus
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