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

BACKGROUND: 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. OBJECTIVE: To histologically assess APM preservation in transplanted hair follicles (HFs). METHODS: 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. RESULTS: 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. CONCLUSION: 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.