Scarring Alopecias: More than meets the eye?
Lichen planopilaris (LPP) is one of the most prevalent forms of scarring alopecia, a group of disorders resulting in irreversible hair loss due to the destruction and fibrosis of hair follicles. The study titled “Scarring Alopecias: Pathology and an Update on Digital Developments” by Donna M. Cummins, Iskander H. Chaudhry, and Matthew Harries et al., published in Biomedicines in 2021, offers comprehensive insights into the pathological mechanisms, diagnostic challenges, and technological advancements in managing scarring alopecias.
Scarring alopecias, including LPP, are characterized by the destruction of the hair follicle’s epithelial stem cell niche, known as the bulge. This region, located at the lower part of the hair follicle just above the attachment point of the arrector pili muscle, contains epithelial hair follicle stem cells (eHFSCs) that are essential for the regeneration and cyclical growth of hair follicles. The destruction of these stem cells in the bulge region leads to permanent hair loss because it prevents the hair follicle from regenerating.
In LPP, the perifollicular inflammatory infiltrate targets the bulge, leading to the collapse of immune privilege.
Immune privilege
Now, this part is important in its own right and it concerns Immune privilege. Immune privilege is a state where certain areas on and in the body are protected from immune system attacks to maintain tissue integrity and function.
This collapse exposes hair follicle antigens to the immune system, resulting in an autoimmune response that damages the eHFSCs.
Now, for a nonscarring alopecia like alopecia areata, this immune privilege collapse seems to occur at the base of the dermal papilla hair follicle. So, in this case, there is no actual destruction of the hair follicle as the stem cell niche bulge is not destroyed. So, using a jak-inhibitor or topical corticosteroid injections in many cases helps the hair come back after a while.
Androgenetic alopecia: new insights into the pathogenesis and mechanism of hair loss - PMC.
Also, Androgenetic Alopecia (AGA) is also a form of non scarring alopecia. But, there is some reason to believe that it eventually becomes a form of scarring alopecia, or perhaps in my thought which I will elaborate later, the condition of AGA, primarily caused by DHT, may be implicated in OTHER HAIR LOSS CONDITIONS. THIS IS MAJOR.
Understanding immune privilege and its collapse is crucial as it underscores why these autoimmune reactions occur and why they lead to irreversible hair loss. The study by Cummins et al. highlights that the destruction of the sebaceous glands is a common early feature in all types of scarring alopecias before significant hair loss occurs.
Sebaceous glands, which are small oil-producing glands connected to hair follicles, play a vital role in maintaining the health and integrity of hair follicles by producing sebum, which lubricates and protects the hair and skin. Their loss or dysfunction is considered an early marker of disease activity and can precede noticeable clinical symptoms of hair loss.
Types of Scarring Alopecias and Sebaceous Gland Destruction
In scarring alopecias such as Lichen Planopilaris (LPP), Frontal Fibrosing Alopecia (FFA), Central Centrifugal Cicatricial Alopecia (CCCA), Discoid Lupus Erythematosus (DLE), Folliculitis Decalvans (FD), and Pseudopelade of Brocq (PsB), the sebaceous glands are among the first structures to be destroyed. This early destruction is significant across various types of scarring alopecias, indicating the onset of irreversible hair loss before the hair follicles are visibly affected.
Lichen Planopilaris (LPP)
From Scarring Alopecias: Pathology and an Update on Digital Developments - PMC , here it shows scar tissue replacing the hair follicle
Lichen planopilaris (LPP) is characterized by a lichenoid inflammatory infiltrate around the isthmus and infundibulum of the hair follicle. The study notes that in LPP, sebaceous glands are typically destroyed early in the disease process, often before significant hair loss becomes clinically apparent. This early destruction leads to perifollicular fibrosis and eventual follicular dropout.
Frontal Fibrosing Alopecia (FFA)
Frontal fibrosing alopecia (FFA), a variant of LPP, also shows early sebaceous gland loss. FFA is marked by a progressive recession of the frontal hairline, and the histological features are similar to those of classic LPP. The study emphasizes that in FFA, the early loss of sebaceous glands and the presence of a lichenoid infiltrate contribute to the progressive and scarring nature of this condition.
Central Centrifugal Cicatricial Alopecia (CCCA)
Central centrifugal cicatricial alopecia (CCCA) predominantly affects women of African descent and presents as a slowly expanding patch of scarring alopecia on the crown or vertex of the scalp. The paper highlights that in CCCA, the sebaceous glands are destroyed early in the disease course, which is a critical factor in the pathogenesis and progression of the condition. The loss of sebaceous glands in CCCA is accompanied by concentric lamellar fibrosis and lymphocytic inflammation around the hair follicles.
Discoid Lupus Erythematosus (DLE)
Discoid lupus erythematosus (DLE) is another form of PCA where sebaceous gland destruction is a prominent feature. Here, the inflammatory process targets the hair follicles and the sebaceous glands, leading to follicular plugging, perifollicular inflammation, and scarring. The study notes that DLE can mimic other scarring alopecias histologically, but the early loss of sebaceous glands and the presence of mucin in the dermis are distinguishing features.
Folliculitis Decalvans (FD)
Folliculitis decalvans is a neutrophilic form of PCA characterized by the destruction of sebaceous glands and hair follicles due to intense inflammatory infiltrates. The study indicates that in FD, the sebaceous glands are among the first structures to be destroyed, followed by the formation of follicular pustules and crusting.
Pseudopelade of Brocq (PsB)
Pseudopelade of Brocq is a less common form of PCA, presenting with small, non-inflammatory patches of alopecia. Although the exact pathogenesis is unclear, early sebaceous gland loss is a feature seen in histological examinations, contributing to the characteristic “footprints in the snow” appearance of the scarring alopecia patches. I’m not sure why but this “strange alopecia” or class of “strange alopecias” are honestly worrisome to me as it could imply environmental factors at play. There simply needs to be more research.
Emphasis of Biopsy… also what’s going on with the sebaceous glands??
Given these conditions, the early identification of sebaceous gland loss through scalp biopsies can serve as an important diagnostic marker; this will guide timely and appropriate interventions to manage and potentially mitigate the progression of scarring alopecias.
https://www.sciencedirect.com/science/article/pii/S2667026722000212
But wait just one moment, why are all of these different kinds of scarring alopecias have a major histopathology similarity - that is the loss of sebaceous glands? Like mentioned before, anatomically speaking, the sebaceous glands are close to the stem cell niche. What is going on with the sebaceous glands for them to become destroyed by white blood cells (lymphocytes primarily) ? When you look at the When you look at the patients themselves, they seem to have different conditions considering how the manifests in phenotype, and yet, they have similar foundations…/.