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.
