Many scarring alopecias are associated with a reduction or loss of SG. Loss of SG seems closely tied to a loss a “stem cells” in hair follicles and a loss of regenerative ability of the hair.
In fact, a pathologist interpreting a scalp biopsy and notes that SG are reduced in any specimen must sound the alarm that a scarring alopecia could potentially be present in that biopsy.
Loss or atrophy of SG appears to be very early step in the disease pathways that lead to lichen planopilaris (LPP). In fact, inflammation in the sebaceous duct (the duct that carries sebum from the gland into the hair canal) is also involved very early on in the course of the disease. Pathways that trigger loss of SG may be happening in LPP even before the inflammation sets in.
Similar to LPP, loss or atrophy of SG appears to be an early feature of frontal fibrosing alopecia (FFA) as well. Reduction in SG is known to occur long before scarring starts to set in (perifollicular fibrosis). In fact, reduction in SG occurs at the same time as inflammation occurs in the tiny vellus hairs. Interestingly, at least for eyebrow hairs, the degree to which SG are lost seems to be correlated with a greater inability to regrow hair with treatment.
In contrast to what we observe in LPP and FFA, loss of SG may be less relevant in the very “early steps” that are driving a different scarring alopecia known as central centrifugal cicatricial alopecia.
Miteva and colleagues showed that approximately 83 % of biopsies from patients with LPP showed a complete absence or markedly diminished presence of sebaceous glands. In contrast, only 43 % of biopsies from CCCA showed loss of sebaceous glands. Therefore, there may be differences is the role of sebaceous gland loss in these two conditions.
The precise molecular pathways the cause the SG to be lost may also differ in different types of scarring alopecia. More research is needed in this area.
Dina Y et al. J. Am. Acad. Dermatol 2018
Miteva M and Sabiq S. Am J Dermatopath 2019.
Katsoulis et al.. J. Am. Acad. Dermatol 2020.
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