Skin lesions in the typical form of lichen planus are characterized by monomorphic flat papules, 2-5 mm in diameter, polygonal in shape, with central depression, pink-red color with a characteristic purple or lilac tint, and a waxy sheen that is more pronounced on lateral illumination. Scaling is usually minimal. A reticular pattern (Wickham's striae) may be seen on the surface of larger papules, especially after wetting with water or petroleum jelly.

A characteristic feature of lichen planus is its tendency to form grouped eruptions, forming rings, garlands, or lines. Less commonly, papules coalesce to form plaques with a pebbly surface. New papules may appear around these plaques, densely or sparsely distributed. In most cases, the rash is symmetrical and often occurs on the inner surface of the forearms, wrists, sacrum, shins, and (especially in men) the genitalia. In some cases, rashes may spread over the entire skin, often to the oral mucosa. The palms, soles, and face are rarely involved. During exacerbations, Koebner's phenomenon may occur, where new nodules develop at sites of skin trauma. Patients may experience pruritus. In some cases, the disease occurs without itching.

Lichen planus usually resolves with the formation of secondary hyperpigmented patches, and sometimes hypopigmentation may remain.

Characterized by formation of plaques with rounded or oval outlines measuring 4-7 cm or more in diameter. Color of these plaques is livid with a purplish tinge. The surface of the plaques is uneven, warty, covered with verrucous projections and numerous depressions. Small purplish-red nodules, characteristic of typical form, may be found at the periphery of main lesions. The lesions are usually localized on the anterior surface of shins, are intensely pruritic, and respond poorly to treatment.

Isolated hyperkeratotic lesions are sometimes seen which, when located on face and upper extremities, clinically resemble senile keratosis or basal cell carcinoma.

Rarely, resolution of papules of lichen planus leads to skin atrophy, or conversely, sclerosis may develop with the formation of keloid-like formations. Skin lesions are more commonly observed on the head, trunk, axillary folds, and genitalia. The eruptions are sparse and consist of typical papules and atrophic patches of purplish and yellowish-brown color. When these elements coalesce, bluish-brown atrophic plaques of 1 to 2-3 cm in size are formed.

Characterized by multiple brownish macules that coalesce into diffuse, occasionally limited reticular, patchy, unilateral linear, and perifollicular lesions. There are typical papules as well as pigmented elements. Common sites include face, neck, and upper extremities, and less commonly, skin folds and creases.

These patches and papules are ash-black, dark brown, brownish-blue in color, irregular in shape and size, and in the early stages have a narrow reddish border. The eruptions are often asymptomatic, sometimes accompanied by pruritus. Lesions progress slowly with no tendency for spontaneous resolution.

Histologically, there is epidermal atrophy, vacuolation of the basal layer, and moderate lymphohistiocytic infiltration in the dermis.

Clinically characterized by formation of vesicles or bullae on plaques and papules on erythematous areas or unaffected skin. The eruptions vary in size and have a thick tense covering that later becomes flaccid and wrinkled. The contents of the vesicles are transparent, slightly opalescent with a yellowish hue, and in some places, contain blood. A distinctive feature of the condition is appearance of blisters both within area of lichen planus plaques and on healthy skin.

Blisters can also appear on oral mucosa, sometimes in isolation, which can complicate the differential diagnosis with pemphigoid. Blisters forming on normal skin are a more characteristic symptom of the pemphigoid variant, and they should be differentiated from the bullous form using direct and indirect immunofluorescence tests.

Characterized by development of erosions on the skin and mucous membranes, often with scalloped edges, ranging in size from 1 to 4-5 cm or more. These ulcerative lesions are often preceded by bullous eruptions. Ulcerative lesions are rare and localized to the lower extremities, accompanied by pain that is aggravated by walking. Edges of the ulcers are firm, pinkish-blue in color, and elevated above the level of surrounding healthy skin. Base of the ulcers is covered with pale, granular tissue and a necrotic layer.

These eruptions are most commonly found on soles, especially in the interdigital spaces. Cases of involvement of trunk and perianal area have been reported. The eruptions leave scars.

This variant often coexists with more typical nail, mucosal, and cutaneous involvement, aiding in accurate diagnosis. Ulcerative lesions may progress to squamous cell carcinoma.

Characterized by appearance of follicular papules primarily on the skin of the trunk, covered with dense horny spines. It can be characterized by follicular keratotic papules alone or coexist with typical papules on the skin and mucous membranes. Follicular papules can be isolated or form plaques.

Clinically, whitish atrophic or scarred patches may be observed on the scalp, which may be accompanied by complaints of increased hair loss, itching, scaling, burning, and tenderness of the scalp. These subjective symptoms may be exacerbated by exposure to ultraviolet light, scalp irritation, sweating, and stress.

Hair is easily removed from affected areas. Patches may be single or multiple and usually involve the crown and vertex of the scalp.

There are three subtypes of flat lichen: classic, frontal fibrosing alopecia, and Graham-Little-Piccardi-Lassueur syndrome.

The classic variant is characterized by patches of alopecia on the scalp and isolated typical patches on the trunk and extremities.

Frontal fibrosing alopecia presents with progressive scarring and hair loss from the frontal hairline and affects primarily middle-aged women.

Graham-Little-Piccardi-Lassueur syndrome is a triad of scarring alopecia of the scalp, widespread follicular papules on the trunk, and nonscarring hair loss in the axillary and pubic regions.

Clinical manifestations of this form of the disease typically develop unnoticed by patient, who may not seek medical attention until months or years after the onset of the disease.

Lichen planus localized on the palms and soles presents atypically. Diagnostic challenges arise in cases of isolated palmoplantar involvement. In these cases, skin thickening develops slowly with or without keratotic deposition resembling callus. Lesions are often localized on lateral areas of the hands and feet, and fingertips, although these are rarely involved.

These eruptions may also appear as small, flat or slightly sunken cornified areas, deeply located vesicles in dyshidrosis and, rarely, as bullous-ulcerative changes that may give rise to vegetative verrucous lesions.

In all these cases, single typical polygonal papular eruptions can be observed, which help in the correct diagnosis.

In rare cases, this form may be associated with areas of scarring alopecia on the hairy part of the scalp.

Observed in 10% of patients. Individual papules and plaques that expand peripherally and resolve in the center, forming rings, with central part hyperpigmented. The rash is most commonly found on the glans of the penis, scrotum, axillary folds, occasionally on the trunk and extremities.

Usually seen in children, characterized by an arrangement of papules in stripes that may be linear, segmental, girdle-like, or following Blaschko's lines. The rash is localized to the trunk, extremities, and rarely face. Individual eruptions may appear as typical pruritic flat papules. Eruptions may also have a reticular, hyperkeratotic, or annular appearance.

Sometimes the cause of this form of the disease is the phenomenon of isomorphic reaction. Zosteriform localization of eruptions is possible, often as a result of previous herpetic infection.

Actinic lichen planus, also known as tropical lichen planus, is common in people from tropical regions (African, Middle Eastern, and Indian populations) and rare in Caucasians. Eruptions are more common in spring and summer, with improvement or remission during the winter months. Actinic form is observed in middle-aged patients, more often in women than in men. The exact pathogenesis is unknown, but sun exposure is clearly an important factor in the development of the disease. There are probably genetic, infectious, environmental or hormonal predisposing factors.

Clinically, it presents in three forms: annular, pigmented, and dyschromic.

The most common annular form is characterized by erythematous brownish annular plaques with or without atrophy. The pigmented form appears as hypermelanotic macules with a melasma-like appearance. The dyschromic form is the rarest and is characterized by appearance of whitish papules that often coalesce into pinhead-sized lesions.

The eruptions are localized on the face, particularly the forehead, cheeks and lips, upper chest, extensor surfaces of the forearms and dorsal surfaces of the hands. Actinic lichen planus is usually asymptomatic and may resemble actinic keratosis.

Erythrodermic form is characterized by sudden erythema of trunk and extremities with elevated temperature, edema, and the appearance of typical lichenoid papular eruptions. Atypical clinical presentation is due either to drug sensitization leading to drug eruption or to a combined course of lupus erythematosus and actinic lichen planus in the axillary and pubic areas. Cases have been reported in which erythroderma developed after extensive needling, sunbathing, and radiation therapy. Classic form of lichen planus may also progress to the erythrodermic stage.

This stage is characterized by diffuse, infiltrated reddish-purple plaques on the trunk, face, and extremities, accompanied by swelling and desquamation, masking the appearance of typical purplish papules, which may be found in small numbers after the process has subsided. In addition to erythroderma, typical elements of lichen planus, bullae and erosions may be observed. The eruptions are accompanied by intense pruritus.

Hypopigmented lichen planus is a rare form of lichen planus considered as a post-inflammatory hypopigmentation. It is characterized by scaly hypopigmented patches, usually round in shape, with hyperpigmentation in the center of the lesions.

Eruptive lichen planus, also known as exanthematous lichen planus, clinically manifests as rapidly spreading, erythematous, flat, polygonal papules or macules of violet color. Subsequently, the lesions resolve, leaving hyperpigmented spots. Typical sites are trunk and upper and lower extremities. It is notable that multiple eruptions show different temporal evolution of individual papules and macules.

Perforating lichen planus is a rare variant of the disease that presents clinically as crusted keratotic papules and plaques with a keratotic plug in the center. Typical localization is shins, ankles and dorsum of the feet. Frequent recurrence of lesions is characteristic.

Nail lichen planus occurs in 10-15% of patients and involves nail plate. It presents as an onychodystrophy with circulatory disorders (dryness, longitudinal ridges, pterygium, complete destruction of the nail plate). Characteristic changes typically develop simultaneously in several nails. In some patients, nail changes precede skin rashes and may even be the only manifestation of this dermatosis, in which case the diagnosis should be confirmed by histopathologic examination.

A classic symptom is the development of a pterygium, in which eponychium grows anteriorly and adheres to proximal part of the nail. This leads to fissuring of the nail and sometimes complete loss of the nail plate.

Another common symptom is trachyonychia, characterized by roughness of the nail plate, loss of transparency, and a grayish appearance.

Less common symptoms include onychoschizia (thinning, appearance of longitudinal lines, and distal splitting of the nail plate), onycholysis, longitudinal ridges (onychorrhexis), subungual hyperkeratosis, and complete disappearance of the nail plate (anonychia), which is seen in the erosive-ulcerative form.

Inverse lichen planus is a rare clinical presentation characterized by discrete reddish-brown macules and papules. These eruptions are localized in the axillary folds, inguinal folds, inframammary folds. Koebner's phenomenon is characteristic.

Clinically, the eruptions have a localized erythematous character with blurred borders and areas of lichenification. Keratotic (horny) papules and erosions with complex contours may be present. Hyperpigmentation is also typical.

Oral lichen planus presents with small, grayish-white papules, up to 2-3 mm in diameter, located symmetrically on mucosa of both cheeks. These papules may coalesce to form a network of whitish reticular bands (Wickham's striae). Plaques with well-defined borders that protrude above the surrounding mucosa, resembling leukoplakia, may also occur (patchy form). When tongue is involved, white papules may be seen that coalesce into small plaques.

Subjective sensations are usually absent in typical form of oral lichen planus, but erosions or ulcers (especially in the elderly) may appear in the affected areas of the mouth, accompanied by a burning or painful sensation and discomfort with hot or cold water.

Hyperkeratotic oral lichen planus is characterized by appearance of hyperkeratotic patches with well-defined borders on the background of typical eruptions or the appearance of verrucous growths on the surface of plaques. Patients may report dryness of the mouth and mild pain when eating hot foods.

This variant is characterized by presence of typical grayish-white papules on an erythematous and swollen mucosa. Common sites include inner surfaces of the cheeks and gums. Eating, especially hot and spicy foods, may be associated with pain.

This form is characterized by presence of small, single or multiple erosions, sometimes ulcers, irregular in shape, covered by a fibrous layer that may cause bleeding when removed. Erosive lichen planus is rare and is often localized on the dorsal and lateral surfaces of the tongue and on both sides of cheeks. Pain associated with these erosions usually is mild. The erosive-ulcerative form is characterized by prolonged presence of erosions and ulcers surrounded by typical papules on a hyperemic and swollen base.

This form manifests as areas of atrophy, most commonly on the lips.

Characterized by coexistence of typical papular eruptions and whitish-pearly blisters, measuring up to 1-2 cm in diameter. Blisters have a dense covering and can exist for several hours to 2 days. After the blisters rupture, rapidly epithelializing erosions form.

This variant presents with involvement of upper lip mucosa in the form of symmetrical foci of limited stagnant hyperemia protruding above the surrounding mucosa. The upper lip is swollen.

In young males, lichen planus sometimes occurs exclusively on genitalia or simultaneously on oral mucosa and genitalia. Genital involvement typically presents with a characteristic clinical appearance and may be localized on the shaft of the penis, foreskin, glans, or scrotum. Ulceration of the affected areas is rare, and the concomitant presence of lichen planus lesions in mouth helps in the differential diagnosis. Circumcision often has a marked therapeutic effect.

This form is relatively common. Lesions may be confined to the genitalia, coexist with oral mucosal involvement, or be part of a widespread process. Clinical manifestations in vulvar region may vary: they may present as the typical linear, reticular (white-gray lacy pattern), annular, or patchy forms of the disease. Alternatively, they may manifest as an erosive form associated with dystrophic changes, scarring, and disruption of normal vulvar anatomy.

A characteristic feature of the vulvovaginal variant is its chronic course with unexplained exacerbations, improvements, and remissions.

Characterized by clinical, histological, and immunopathological features of both classic lichen planus and bullous pemphigoid. The oral mucosal lesions of bullous pemphigoid may resemble those of lichen planus both clinically and histologically. Clinically, tense blisters are observed on both unaffected skin and skin affected by preceding or concurrent lichenoid eruptions. The rash is most common on the extremities, but can occur anywhere, including the oral mucosa. Histologic examination of affected tissue reveals features of both lichen planus and bullous pemphigoid.

Characterized by simultaneous occurrence of lichen sclerosus and lichen planus in anogenital area, often involving the vulva. In addition to patches of lichen sclerosus, there are classic pruritic, purplish, polygonal papules of lichen planus.

Characterized by coexistence of clinical features of lichen planus and discoid lupus erythematosus. Systemic lupus erythematosus may develop in some of these patients. Common areas of involvement are distal extremities, face, and trunk, with hands and feet. A common combination is the butterfly rash on the face and characteristic lichen planus eruptions on the limbs.

Lichenoid drug eruptions may occur with oral administration, parenteral injection, and inhalation of drugs. The exact pathogenetic mechanism underlying the development of it is not fully understood. However, they are thought to be a direct effect of clones of autoreactive cytotoxic T cells directed against drug/antigen complexes recognized as foreign by keratinocytes and Langerhans cells.

Lichenoid eruptions typically occur several weeks or months after initiation of therapy. The nature of the eruption depends on drug dosage, patient response, re-exposure to the drug, and concomitant use of other medications. Drug-induced lichenoid eruptions are usually indistinguishable from classic lichen planus (multiple flat, pruritic, purplish papules) and tend to involve large areas of skin, even progressing to erythroderma.

Lesions are usually symmetrical on the trunk and limbs and, unlike lichen planus, do not involve body folds. They rarely occur on oral mucosa and lack the classic Wickham's striae. Persistent postinflammatory pigmentation is also characteristic, and sometimes alopecia and skin atrophy with anhidrosis due to sweat gland atrophy may occur.

Resolution of the rash is slow, typically within 1 to 4 months and sometimes up to 2 years. Occasionally, lichenoid drug eruptions may resolve spontaneously or periodically, even with continued use of the drug.

Eruptions that are clinically indistinguishable from lichen planus occur initially at sites of contact with a chemical substance or medication and may subsequently spread to other areas of the body; mucosal involvement is usually absent. The most common causes include paraphenylenediamines (used in color film processing) - this reaction occurs in 25% of cases, methacrylate esters (used in engineering and dentures), metals (nickel, chromium, gold, cobalt), and certain medications (aminoglycosides, mercury-containing preparations). Resolution of affected areas is slow, taking several years, and post-inflammatory pigmentation may persist for years.

Graft-versus-host disease that develops three months after transplantation may manifest as lichenoid eruptions that are clinically and histologically indistinguishable from lichen planus. Lichenoid eruptions are predominantly localized on the trunk, buttocks, thighs, shins, palms, and soles.