Using biopsies to study the differences between two hair loss disorders: lichen planopilaris and frontal fibrosing alopecia

Lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA) are two uncommon disorders that both cause permanent, scarring alopecia (hair loss) and inflammation of the hair follicles. LPP affects both sexes and typically causes patchy alopecia over the central scalp, whereas FFA generally affects women and causes the hairline at the front of the scalp to recede. It can also cause eyebrow and body hair loss. Despite these distinct phenotypes (physical characteristics), FFA has traditionally been regarded as a variant of LPP. The authors sought to distinguish the two conditions using a wide array of markers for different cell types around the hair follicles. Markers are substances in the body, such as certain proteins, which act as signs to show, for example, the presence of certain cells or inflammation. The authors took skin punch biopsies (a type of tissue sample) from affected areas of scalp in patients with a diagnosis of LPP or FFA, and from healthy controls (people without LPP or FFA). In this study, the authors present a detailed, systematic analysis of a range of key inflammatory cell markers in LPP, FFA and controls. There were many similarities in the numbers and type of inflammatory cells in the two conditions. The study focussed on the different types of cells called macrophages seen in LPP and FFA. Broadly, these cells can be divided into two types, M1 cells, associated with inflammation and cell death, and M2 cells, involved in tissue repair. The two conditions differed in that more markers for M2 cells were seen in LPP in comparison to FFA. The authors hope that therapies directed against specific macrophage cell types may be developed in the future, preventing irreversible hair loss. Linked Article:   Harries et al. Br J Dermatol 2020; 183 :537–547.