Lichen Planopilaris

Abstract

Lichen planopilaris (LPP), a follicular form of lichen planus (LP), is a primary lymphocytic cicatricial alopecia characterized by irreversible hair loss and scarring. Several mechanisms have been implicated involving deficient peroxisome proliferator-activated receptor (PPAR) followed by destruction of the pilosebaceous unit, CD-8+ T-cell-induced apoptosis of the epithelial follicular stem cells (eHFSCs) that have lost their immune privilege (IP) and epithelial mesenchymal transition of the follicular eHFSCs, which have survived the massive apoptosis. The bulge IP collapse in LPP shows striking similarity to the bulb IP collapse in alopecia areata. Clinically, several subtypes have been described including patchy (one or more patches that start on vertex and expand (Figure 13.1), diffuse (the vertex is initially affected but patches can occur anywhere), patterned or fibrosing alopecia in a pattern distribution (FAPD) (overlap between diffuse LPP and androgenetic alopecia). Other forms include linear LPP (Figure 13.1), which can simulate morphea en coup du sabre and linear lupus profundus; Graham-Little-Picardi-Lasseur syndrome (a triad of LPP on scalp, non-scarring alopecia of the axillary and pubic hair, and widespread follicular papules – lichen planus spinulosus); LPP can also rarely occur in children where it is usually misdiagnosed as alopecia areata or tinea capitis on clinical exam (Figure 13.2). The main differential diagnosis includes keratosis follicularis spinulosa decalvans (KFSD), which is a rare genetic condition of X-linked inheritance (but sporadic and autosomal dominant cases may occur), with onset during childhood that presents with keratotic follicular papules on the body, scarring alopecia on the scalp, eyebrows and progresses over puberty (Figure 13.3). Hypopigmented macules on scalp with associated alopecia have been reported as a subtype of LPP on the scalp in African-American patients (Figure 13.4). Figure 13.1 (A) Patchy LPP and (B, C) linear LPP on the scalp and face in another patient. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_1.tif"/> Figure 13.2 (A) A case of biopsy proven LPP in a 10-year-old child that has been misdiagnosed as tinea capitis. (B) The site of trichoscopy-guided scalp biopsy shows peripilar casts (×10). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_2.tif"/> Figure 13.3 (A–C) Keratosis follicularis spinulosa decalvans. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_3.tif"/> Figure 13.4 Hypopigmented LPP in an African-American patient. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_4.tif"/> LPP can be associated with frontal fibrosing alopecia (FFA) in 16–21% of the cases. FFA and FAPD are discussed in Chapters 14 and 15. Folliculitis decalvans lichen planopilaris phenotypic spectrum (FDLPPPS) refers to cases of lymphocytic scarring alopecia showing dual clinical, trichoscopic and histologic features for FD and LPP (see below). LPP can be underdiagnosed prior to hair transplant if not biopsied and this could lead to loss of the follicular grafts after hair transplant (see Figure 13.17). On trichoscopy, there are loss of follicular openings, peripilar casts (tubular scales entangling the proximal 2–3 mm of the hair shaft emergences 90(Figure 13.5), elongated linear blood vessels (Figure 13.6), tufts of hairs (usually 2–4 hairs emerging from the same ostium and surrounded by peripilar casts) (Figure 13.6). In skin types IV-VI, there are blue-gray dots in a target pattern that correspond to pigment incontinence in follicular proximity vs. blue-gray dots in a speckled pattern in discoid lupus erythematosus (DLE) that correspond to interfollicular interface pattern with pigment incontinence (Figure 13.7). White dots correspond to fibrotic tracts replacing individual follicular ostia usually at the margin of the active patch (Figure 13.8) and milky white areas (strawberry ice cream color) correspond to larger areas of follicular scarring. Figure 13.5 Peripilar tubular casts encircling the proximal portions of the hair shafts. Hair casts (arrow) are noted along the length of some hair shafts (×10). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_5.tif"/> Figure 13.6 Linear vessels in LPP (black arrow) and tufts of 2–3 hairs coming out of the same emergence (red arrow) (×10). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_6.tif"/> Figure 13.7 Blue-gray dots in a peripilar target pattern in LPP (A, ×40) that corresponds to folliculocentric involvement on histology (C), and in a speckled pattern in DLE (B, ×10) due to the interfollicular interface dermatitis (D). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_7.tif"/> Figure 13.8 (A) White dots on trichoscopy (×10) corresponding to (B) the fibrotic tracts replacing the existing follicles on histology (arrows). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429457609/a1a07c34-5530-453d-aca4-02e4ee680a4a/content/fig13_8.tif"/>