Acid‐Fast (Ziehl‐Neelsen) Staining Facilitates Follicular Counting in Horizontally‐Sectioned Scalp Biopsies.

Abstract

Transverse sectioning of scalp biopsies was first proposed by Headington in 1984. Horizontal sections allow easy analysis of follicular density, accurate determination of hair shaft diameter, and quantification of the anagen:telogen ratio. The terminal to vellus hair (T:V) ratio is an important parameter in the differential diagnosis of non‐scarring alopecias. A vellus hair is defined as having a cross‐sectional diameter of 0.03 mm or less, and a diameter not exceeding the thickness of its root sheath. It is tedious to tally the T:V ratio in a standard 4 mm punch biopsy because the entire biopsy can only be visualised using the 2x and 4x objectives. It is difficult to identify vellus hairs with this magnification, and one must switch between high and low power, often losing track of which hairs have already been counted. All hair shafts are strongly acid‐fast and stain bright red, making it easy to count terminal and vellus hairs with 2x and 4x magnification. We show acid‐fast (Ziehl‐Zeelsen) stained slides from various types of non‐scarring alopecias cut at the level of the infundibula, and contrast these to hematoxylin and eosin stained slides at the same level, to demonstrate how acid‐fast staining greatly facilitates follicular counting.