Perifollicular Inflammation and Fibrosis in Androgenetic Alopecia: Implications for Diagnosis and Treatment - A Comparative Histopathologic and Clinical Study with Normal-Appearing Scalp

Sanusi Umar,1– 3 Belinda H Tan,4 Paul K Shitabata1,2,5 1Department of Medicine, University of California at Los Angeles, Los Angeles, CA, USA; 2Division of Dermatology, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA, USA; 3Dr. U Hair and Skin Clinic, Manhattan Beach, CA, USA; 4People Science Inc., Los Angeles, CA, USA; 5Dermatopathology Institute, Torrance, CA, USACorrespondence: Sanusi Umar, Dr. U Hair and Skin Clinic, 2121 N. Sepulveda Avenue, Suite 200, Manhattan Beach, CA, 90266, USA, Tel +1310318-1500, Fax +1310318-1590, Email drumar@dru.comIntroduction: Androgenetic alopecia (AGA) is traditionally regarded as a noninflammatory, androgen-driven condition. Yet clinical and histologic evidence identifies a subset of patients with perifollicular infundibulo-isthmic lymphocytic infiltrates and fibrosis (PIILIF), a histopathologic pattern resembling early primary cicatricial alopecia (PCA). This study evaluates the clinical, histologic, and immunophenotypic features of PIILIF and their diagnostic and therapeutic implications.Methods: This retrospective study of 129 AGA patients drawn from a referral center, obtained trichoscopy-guided biopsies from balding and clinically non-alopecic scalp (cNAS). Histopathologic and immunohistochemical findings were correlated with clinical features and treatment outcomes. Patients with PIILIF received multimodal therapy targeting androgenic and inflammatory pathways. The cohort, from a specialty clinic, included both typical and treatment-resistant AGA.Results: PIILIF was identified in the cNAS of 81% of patients, particularly in those aged 44 or older, with Norwood stage ≥ 5, or with prior poor response to therapy. Histology showed CD117+ mast cells, perifollicular CD4-predominant lymphocytes and fibrosis in the infundibulo-isthmic unit. Combination therapy using dihydrotestosterone blockade plus anti-inflammatory agents modeled after PCA therapies, including tetracyclines, topical calcineurin inhibitors, and select phytoactive botanicals, yielded greater improvement than standard AGA treatment regimens alone. Overall, 67% improved, and 2% had suboptimal outcomes (p < 0.0001). These findings support an AGA-PIILIF continuum that may include fibrosing alopecia in a pattern distribution.Conclusion: PIILIF represents an under‑recognized inflammatory endotype within AGA that may account for treatment resistance in some patients. Early biopsy can confirm the diagnosis, and therapy targeting hormonal and immune pathways may improve outcomes. Routine trichoscopy with a low threshold to biopsy perifollicularly abnormal units showing mild erythema, scale, or hyperpigmented collars can guide care, particularly in treatment resistant or equivocal cases. The broader systemic implications of this inflammatory signature merit further investigation.Plain Language Summary: Pattern hair loss is usually linked to hormones. Yet some people do not improve with standard treatment. We asked whether an immune type of inflammation, similar to what doctors see in scarring alopecias, might be present in these patients.We studied 129 adults with pattern hair loss. Using a magnified scalp exam, we took tiny skin samples from thinning areas and from nearby skin that looked normal.Most patients, 81%, had immune inflammation around the upper part of follicles with early scarring, even where the scalp looked normal. This differs from the mild, nonspecific inflammation sometimes seen in long-standing baldness. It was more common after age 44 and with advanced thinning. On magnified exam, a reddish ring, a darker ring in skin of color, or fine scale was common but not predictive, and redness faded with pressure.People did better when treatment targeted both hormones and this immune inflammation. The anti-inflammatory medicines were the same types used for scarring alopecias, such as tetracyclines, topical calcineurin inhibitors, and selected botanical agents, together with blockers of dihydrotestosterone. Overall, 67% improved, and 2% had a poor result.What this means is that an immune, scarring-type process can coexist with hormone-driven hair loss and may help explain treatment resistance in some patients. It also supports that, when treatment is not working or the exam is unclear, a biopsy can confirm the diagnosis and guide care. Early targeted therapy may improve outcomes.Keywords: androgenetic alopecia, hair loss treatment, hair transplant failure, scarring alopecia, primary cicatricial alopecia, dihydrotestosterone, male pattern baldness, female pattern hair loss