1.5.4 Lichen planus

Idiopathic subacute to chronic immune-mediated inflammatory dermatosis involving the skin, mucosae, nails and/or hair.

The etiopathology has not been fully elucidated. Very likely it is an autoimmune disorder, thus associations with collagen-vascular diseases, vitiligo and diabetes mellitus are not surprising. Graft-versus-host-disease (GvHD) has similar morphology. An autoimmune biphasic process primarily mediated by CD 4 and CD8 T lymphocytes with cytotoxic mechanisms in response to exogenous or self-altered antigens presented by antigen-presenting cells, such as plasmacytoid dendritic cells (DCs) followed by secretion of type I interferon alpha is currently favoured. Cytotoxic (Th17 and Tc17) lymphocytes by releasing IL–12 and IL–23 are main players. Hepatitis B and C, stress and various drugs may also play a role in its induction in some cases. T-cells accumulate in the upper dermis belonging to the CD4+ and CD8+ subtypes. T-cells, both CD4+ and CD8+, accumulate in the upper dermis. Via secretion of several cytokines apoptosis of basal epidermal cells appear. IFNγ drives the disorder, thus defining LP as a Th1 dominated disorder.

• Five P disease (Pruritic, purple, polygonal, planar papules),

• Skin: polygonal violaceous papules, white net-like superficial markings (Wickham’s striae) marked pruritus.

• Mucosae: lips, tongue, cheeks, genital and anal areas (annular, bullous, erosive, atrophic), net- like white, non-removable pattern.

• Nails: non-specific changes (longitudinal stripes, trachyonychia) but also scarring (pterygium formation, atrophy, anonychyia).

• Scalp: lichen planopilaris /lichen planus follicularis decalvans (atrophic scarring alopecia; pseudopelade).

• Palmoplantar: hyperkeratosis (fissured).

Flexor aspects of wrists, nails, oral and genital mucosae. Palms and soles.

Types:

• Lichen planus exanthematicus -> erythroderma (exfoliative dermatitis),

• Hypertrophic lichen planus (lichenification because of chronic rubbing, especially on shins),

• Annular or linear lichen planus,

• Lichen planus pigmentosus,

• Nodular lichen planus,

• Atrophic lichen planus (confluent, widespread involvement),

• Lichen planus pemphigoides (with antibodies to basement membrane zone),

• Erosive lichen planus (bullous, without antibodies),

• Actinic lichen planus (hyperpigmentation in sun-exposed sites of individuals of colour).

Increased Interleukin-6 (IL-6) in serum (not tested on routinary basis).

Lichenoid drug reactions: Skin eruptions caused by commonly used medications can resemble lichen planus. Histopathology shows parakeratosis and eosinophils. Quinine in tonic water and over-the-counter leg cramp medicines can cause a lichen planus–like condition.

In the mouth, allergy to the metals in fillings and oral appliances can cause sores that look exactly like oral lichen planus.

Prevention: Control of predisposing factors.

• Topical: high potency corticosteroids, calcineurin inhibitors (mucosal disease; strong evidence), tazarotene, calcipotriol, UVA/B, PUVA, UVA1.

• Systemic: corticosteroids (moderate evidence), PUVA, dapsone, hydroxychloroquine, methotraxate, mycophenolate mofetil, acitretin, alitretinoin, ciclosporin, azathioprine, apremilast, sedatives, (enoxaparin, antimycotics).

TNF blockers exhibit fairly controversial effects in lichen planus, since they can trigger pro-inflammatory reactions: TNF-alpha inhibitors may precipitate lichenoid reactions through disruption of a delicate balance between TNF-alpha and interferon-alpha in susceptible patients. More recent studies focus on Janus kinase inhibitors such as tofacitinib, phosphodiesterase-4 inhibitors such as apremilast, and biologics targeting the interleukin-23/interleukin-17 pathway.