Lichen planus

In this post we will deal with another common skin disease - Lichen planus.

• it is chronic inflammatory skin disease.
• Lichen refers to a tree moss while planus is Latin for flat = like a flat tree moss.

For convenience we divide the topic into parts:

1. definition
2. histopathology
3. pathogenesis
4. clinical features
5. treatment

Lichen planus:

• Lichen planus is a chronic inflammatory mucocutaneous disease and presents itself in the form of lesions or rashes.
• Lesions of lichen planus may be described using the six "Ps": pruritic, polygonal, planar, purple papules and plaques.
• The flexor surfaces of the extremities, particularly the wrists, are common locations for lichen planus.

histopathology:

Lichen planus is characterized by:

• The epidermis is hyperkeratotic with irregular acanthosis and focal thickening in the granular layer.(wedge-shaped hypergranulosis)
• The upper dermis has a bandlike infiltrate of lymphocytic (primarily helper T) and histiocytic cells with many Langerhans cells at the dermal-epidermal junction.
• the lymphocytes are intimately associated with basal keratinocytes , which shows degeneration ,necrosis & resemblance in size & contour to more mature cells of Stratum spinosum. this is SQUAMATIZATION.
• as a consequence to this destructive infiltration ,results in redifining of normal smoothly undulating configuration of dermoepidermal junction to more angulated zig-zag contour ("saw-tooth" appearance of the rete pegs)

civatte bodies:

• anucleate ,necrotic basal cells become incorporated into inflamed papillary dermis -these are civatte bodies or colloid bodies.
• these are characteristic of lichen planus (but can be found in any chronic dermatitis where basal keratinocytes are injured)
• In addition to apoptotic keratinocytes, colloid bodies are composed of globular deposits of IgM (occasionally immunoglobulin G [IgG] or immunoglobulin A [IgA]) and complement.

Pigment incontinence due to damage of basal keratinocytes and melanocytes.(this leads to hyperpigmentation of lesion)

pathogenesis:

• LP is a cell-mediated immune response of unknown origin.. The pathogenesis of LP is immunologically mediated. Whether the foreign antigen is a virus or a drug is not known. Langerhans cells process antigens, which are then presented to T lymphocytes. This stimulated lymphocytic infiltrate is epidermotropic and attacks keratinocytes. During this lymphocytotoxic process, the keratinocytes release cytokines that attract more lymphocytes. This process has been referred to as the lichenoid tissue reaction. In addition, recent studies reveal a disruption in the epithelial anchoring system.
• as in psoriasis ,the whole skin is abnormal ,therefore koebners phenomenon (trauma causes appearance of lesions at the site)seen.
• Lichenoid drug eruptions are reactions that may occur after exposure to various medications. These eruptions may exhibit a cutaneous and histologic appearance identical to that of idiopathic lichen planus and, thus, must be considered in every patient with lichen planus. While an exhaustive list of possible offending agents is quite long, the most common include

1. gold,
2. antimalarial agents,
3. penicillamine,
4. thiazide diuretics,
5. beta blockers,
6. nonsteroidal anti-inflammatory drugs,
7. quinidine and
8. angiotensin-converting enzyme inhibitors.

• it is also associated with hepatitis C infection.

clinical features:

• cutaneous lesions consist of itchy ,violaceous ,flat -topped papules that may coalesce focally to form plaques.multiple lesions ,symmetrically distributed
• skin lesions can occur anywhere ,but there is predeliction for wrists ,shins ,lower back &genitalia
• Characteristic fine, white lines, called Wickham stria(due to hypergranulosis), are often found on the papules(see the white lines in the picture below)
• nail involvement causes pemanent deformity or loss of fingernails.

{note:The major point of distinction of lichen planus from eczema, psoriasis, and other common rashes is its color -- violet.}

• In addition to the cutaneous eruption, LP can involve the mucous membranes, the genitalia, the nails, and the scalp.
• Lesions are most commonly found on the tongue and the buccal mucosa; they are characterized by white or gray streaks forming a linear or reticular pattern on a violaceous background.

{note:Oral lichen planus may predispose to the development of squamous cell carcinoma within lesions}

Lichen planopilaris

• Lichen Planopilaris(of hair) is the specific name given to lichen planus on the scalp that may cause permanent, scarring alopecia.
• The hair follicles are destroyed and regrowth of hair will not occur.

treatment:

• In more than 50% of patients with cutaneous disease, the lesions resolve within 6 months, and 85% of cases subside within 18 months. On the other hand, oral LP had been reported to have a mean duration of 5 years. Large, annular, hypertrophic lesions and mucous membrane involvement are more likely to become chronic.
• Patients with localized lichen planus are usually treated with potent topical steroids,
• while systemic steroids are used to treat patients with generalized lichen planus.
• A topical corticosteroid is considered first-line therapy for patients with oral lichen planus.