Definition/Introduction
Basic skin lesions are divided into primary, secondary, and special types. The term lichenification is a secondary skin lesion characterized by skin thickening, hyperpigmentation, and exaggerated skin lines. Lichenification can be further divided into primary and secondary types, wherein primary lichenification signifies lichen simplex chronicus, also known as neurodermatitis circumscripta. On the other hand, secondary lichenification occurs in atopic dermatitis, infective eczematous dermatoses, psoriasis, psoriasiform dermatosis, xerosis, pityriasis rubra pilaris, porokeratosis, vegetative growths, anxiety, and obsessive-compulsive disorders.[1][2][3]
The lesions start as hyperpigmentation on a flat skin surface, followed by the appearance of multiple small papules, termed pseudopapules, giving the lesions a pebbly appearance. The next is thickening or induration of the deep layers of the skin that does not involve the skin creases, thereby imparting a characteristic exaggeration of skin markings. Lesions appear ill-defined, except in certain cases of secondary lichenification.[4][5]
Owing to the inciting factor of chronic rubbing, lichenification often occurs in easily accessible sites such as the nape of the neck, wrists, hands, forearms, waist, scrotum, vulva, thighs, lower legs, and dorsa of feet.[6] Certain cases are known to occur in the lower eyelids, postauricular area, axillae, and popliteal fossae.[7][8]
Diffuse types of lichenification have been described wherein involvement of the face, neck, chest, abdomen, flanks, arms, forearms, thighs, and lower legs appears as ill-defined plaques, ranging from hyperpigmented patches, numerous flat-topped papules, and indurated plaques, which may present symmetrically with extremity involvement.[9][10]
Issues of Concern
The presence of lichenified plaques in a healthy individual necessitates a workup for systemic disorders that present as chronic pruritus and psychological evaluation for anxiety, obsessive-compulsive disorders, or psychogenic disorders.[11][12] Diffuse lichenification can be a manifestation of cutaneous T-cell lymphoma, particularly the folliculotropic type, and of Sezary syndrome.[13][14]
Reports of chronic pruritus as a paraneoplastic phenomenon necessitate thorough screening in cases with a high index of suspicion. These include [15]:
Clinical Significance
Lichenification can be a clinical sign of underlying systemic disorders necessitating workup for psychological, malignant, metabolic, and even autoimmune disorders.
Lichenification makes up part of the minor criteria under Hanifin and Rajka’s criteria for the diagnosis of atopic dermatitis. Other signs of close similarity include the Dennie-Morgan fold, anterior neck folds, and hyperlinearity of the palms and soles.[16]
The classical leathery or tree bark sign in lichen simplex chronicus represents lichenification.[6][17]
