Abstract

Introduction: Qualitative criteria for the diagnosis of traction alopecia have been published, but precise numerical data to support these criteria have not been established. Such data become especially important when evaluating biopsy specimens that may show more than one diagnosis (multifactorial alopecia; MFA). Determining pathologic criteria requires the comparison of a pathologic state with the findings in normal scalp. Methods: 23 cases of traction alopecia were selected from a single dermatopathology practice, de-identified, and compared with 25 cases with the microscopic diagnosis of “normal scalp.” For both “traction” and “normal” cases, these diagnoses were supported by provided clinical information and/or clinical photographs when available. All biopsy specimens were 4 mm in diameter. Results: For normal scalp, the average number of follicular units (FU) was 10.6, and the average number of FU containing less than 2 follicles (FU<2) was 0.48. The average terminal: vellus (T:V) ratio was 4.5:1. For traction alopecia the average number of FU was 9.4, the average number of FU<2 was 6.26, and the average T:V was 1.9:1. Sebaceous glands were intact in all FU in all specimens. Conclusion: Our study is the first to quantify diagnostic criteria in TA. The T:V ratio is reduced in TA compared to NS, presumably because of the expected dropout of terminal hairs in TA. However, the total number of vellus hairs is similar in both groups. There is a significant difference in the number of FU<2, which can be used as a reliable tool when diagnosing TA, especially in the setting of MFA where multiple diagnoses are present within the same patient. We propose a threshold of greater than three FU<2 with intact sebaceous glands as diagnostic for a component of TA.

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