LICHEN SIMPLEX CHRONICUS
Lichen simplex chronicus is a commonly encountered chronic dermatosis that can be initiated by many events. Certain regions of the body are more prone to develop lichen simplex chronicus, such as the lower leg and ankle region and the posterior scalp, but it can occur anywhere. The initiating factor can be any skin insult that induces itching. The itch-scratch cycle is never broken, and the skin in the region being manipulated takes on a lichenified appearance. This is believed to be a localized skin condition that has no systemic associations or causes. Many therapies have been attempted with varying rates of success.
Clinical Findings: There is a slight female preponderance and no racial predilection. Most patients who present with lichen simplex chronicus do not relate an underlying insult that initiated the chronic itching. Some report a previous bug bite, trauma, or initiating rash such as allergic contact dermatitis caused by poison ivy. Involvement is localized to one region of the body, most often the ankle. Other commonly involved areas are the occipital scalp and the anogenital region. Patients report that they have a constant itching or burning sensation, and they respond to it by chronically rubbing or itching the area. Initially, a fine red patch with some excoriations is present. As the condition becomes chronic, the rash takes on the clinical appearance of lichen simplex chronicus. The skin becomes thickened and lichenified. There is an accentuation of the normal skin lines, and the region of involvement shows varying degrees of hyperpigmentation. Small excoriations and even small ulcerations may occur if the pruritus is severe and the patient cannot control the itching.
The cycle of pruritus and itching is perpetuated and can last for years to decades if untreated. Patients often relate that stressful events can initiate a flare of preexisting lichen simplex chronicus. They also commonly state that the itching is worse during the evening hours just before sleep. The main theory to explain this is that the cortex is not as busy processing information at that time, and other areas of the brain that are responsible for itching become activated or become disinhibited from cortical control. Even with treatment, some cases last for years. Patients typically become frustrated with therapy and are willing to pursue the help of other physicians or ancillary medical caregivers, such as acupuncturists. A fully developed area of lichen simplex chronicus is a well-defined lichenified plaque with excoriations and blood-tinged crust.
Pathogenesis: The exact pathomechanism of development of lichen simplex chronicus is unknown. Initiating events have been investigated, including insect bite reactions, underlying atopic diathesis, anxiety, stressful events, and other psychiatric conditions. Many patients have none of these factors, yet the clinical and pathological picture is identical.
Histology: The epidermis is acanthotic with elongation of the rete ridges. A varying amount of parakeratosis is present, with excoriations and superficial ulcerations observed in some cases. The collagen bundles within the papillary dermis show a vertical arrangement, parallel to the rete ridges. The rete ridges are irregular in elongation, unlike the regular pattern seen in psoriasis. A varying degree of epidermal spongiosis is seen, but no epidermotropism. The inflammatory infiltrate is composed primarily of lymphocytes.
Treatment: Therapy is often directed at breaking the itch-scratch cycle. This is attempted with a combination of topical high-potency corticosteroids and oral antihistamines or gabapentin. The sedating antihistamines work better than the newer, nonsedating ones. Topical steroids may be used under occlusion for better penetration of the lichenified region. Intralesional injection with triamcinolone may be attempted. Capsaicin, which is derived from capsicum peppers, may be used. This agent works by depleting the superficial nerve endings of substance P, the neurotransmitter required for the itching sensation. Patients should be advised to trim their fingernails to help prevent trauma when they scratch. Behavioral modification may be attempted, but it is best accomplished by a professional psychiatrist or psychologist. Precipitating causes such as stress should be addressed. Patients often have remissions with frequent relapses.