Histopathology of Lichen Planus and Lichenoid Drug Eruptions

Overview / Definition Lichen Planus (LP) is a chronic inflammatory condition that primarily involves the skin, mucous membranes, hair follicles, and nails. It is characterized histologically by a band-like infiltrate of lymphocytes at the dermal-epidermal junction, liquefactive degeneration of the basal cell layer, and a characteristic appearance of "sawtooth" changes in the epidermis. Lichenoid drug eruptions are similar in appearance to LP but are caused by drug reactions. Epidemiology LP affects individuals of all ages, but it is most commonly seen in adults between the ages of 30 and 60. The condition is slightly more prevalent in women than men. Lichenoid drug eruptions can occur in any age group and are associated with various medications, including NSAIDs, beta-blockers, and certain antibiotics. Incidence: LP has an estimated incidence of 0.5% to 2% in the general population. Gender: LP is more common in females. Age: Peak incidence occurs between 30-60 years. Pathophysiology / Mechanism The exact etiology of LP remains unclear, but it is thought to be an autoimmune process where T-lymphocytes attack the basal cell layer of the epidermis. The lichenoid drug eruptions can be attributed to hypersensitivity reactions to specific drugs, leading to similar inflammatory responses. Immune response: Activation of CD8+ T-cells and cytokine release. Genetic factors: Potential associations with HLA-DR6 and other genetic markers. Drug-induced mechanisms: May involve both Type IV hypersensitivity and non-immune mechanisms. Clinical Presentation LP typically presents as pruritic, polygonal, flat-topped papules, often with a characteristic violaceous hue and white streaks (Wickham's striae). Lesions can appear on various body parts, including the wrists, ankles, and oral mucosa. In contrast, lichenoid drug eruptions may present with similar morphology but often have a more acute onset and can be associated with a recent medication history. Skin findings: Papules, plaques, a