Can Transplanted Hair Follicles Survive in the Absence of Arrector Pili Muscle Attachments?

The arrector pili muscle (APM) is a key structural component of the pilosebaceous unit and follicular stem cell niche. However, its fate after hair transplantation (HT) remains poorly understood.

To histologically assess APM preservation in transplanted hair follicles (HFs).

Scalp biopsies from recipient and native donor areas of 5 patients with suboptimal graft survival after HT were analyzed. Two 4-mm punch biopsies were obtained in each case for horizontal and vertical sectioning. The presence of APMs associated with follicular units (FUs), proximal and distal APM attachment sites, and peri-APM inflammation were evaluated.

A total of 78 FUs were examined. In recipient areas after FU excision (FUE) and FU transplantation, identifiable APMs were associated with 17.2% and 30.0% of FUs, respectively, compared with 25.6% in native occipital donor areas. Although identified muscle fibers appeared continuous, normal proximal and distal attachment sites were not visualized in any specimen.

Transplanted HFs may persist despite absent or disrupted APM architecture, suggesting that complete preservation of native APM anatomy may not be essential for ongoing HF survival after HT.