Chronic diffuse telogen hair loss is common in women. Paired 4-mm punch biopsy from the vertex scalp for horizontal and vertical sectioning is commonly used to distinguish between chronic telogen effluvium (CTE) and female pattern hair loss (FPHL). FPHL is now the favored term for androgenetic alopecia in women.

To evaluate the reliability of a single horizontally sectioned scalp biopsy in the diagnosis of FPHL, 207 women presenting with chronic diffuse hair loss had three 4-mm punch biopsy specimens taken from immediately adjacent skin on the mid scalp, and all 3 biopsy specimens were sectioned horizontally. Findings were compared with 305 women who underwent two biopsies, with one sectioned horizontally and the other vertically. The terminal to vellus-like hair ratio (T:V) at the mid-isthmus level was used to diagnose FPHL (T:V <4:1), CTE (T:V >8:1), or indeterminate hair loss (T:V=5:1, 6:1, or 7:1). To correlate the histologic diagnosis with the clinical severity, a mid-scalp clinical grading scale was developed.

Among the 305 women who had a single horizontal scalp biopsy, 181 (59%) were diagnosed as having FPHL, 54 (18%) having CTE, and 70 (23%) having indeterminate hair loss. Six hundred twenty-one horizontal biopsy specimens were assessed from 207 patients. On the basis of consensus over 3 biopsies, 159 (77%) were diagnosed as having FPHL, 44 (21%) having CTE, and the remaining 4 women (2%) as having indeterminate hair loss. Among these 207 women, 114 were assessed clinically as having stage 1 or 2 hair loss. Sixty-nine (60%) were diagnosed as having FPHL on the basis of triple biopsy, 42 (37%) having CTE, and 2 having indeterminate hair loss. Ninety-three were graded as having stage 3, 4, or 5 hair loss. FPHL was diagnosed in 90 women (97%), CTE in 2, and indeterminate hair loss in one. By using each single biopsy as the criterion for diagnosis, 398 (61%) were classified as FPHL, 99 (16%) as CTE, and 124 (20%) as indeterminate. In 493 biopsies (79%), the single biopsy conclusion was identical to the 3 biopsy conclusions. Where disagreement was seen (21%), most were classified as indeterminate, rather than as a wrong diagnosis (3.3%).

Application of these diagnostic criteria achieved accurate diagnostic definition in 98% of women with triple horizontal biopsies versus 79% with single horizontal biopsy. Ninety-seven percent of women with a mid-scalp clinical grade of 3, 4, or 5 were given a diagnosis of FPHL on triple biopsy. Scalp biopsy for diagnosis should be reserved for women with a mid-scalp clinical grade of 1 or 2.