Lichen simplex chronicus
Synonyms and keywords: Neurodermatitis, neurodermatitides, circumscribed neurodermatitis, circumscribed neurodermatitides, localized neurodermatitis, localized neurodermatitides

# Overview
Lichen simplex chronicus (LSC) is a chronic skin condition associated with a persistent itch-scratch cycle, leading to a thick, leathery, dark (lichenified) skin. Similar to many other skin conditions, it may present with associated dryness, scaling, or erythema. Commonly affected regions include neck, ankles, extremities, scalp and genital region. The incidence and prevalence of the condition are not well established, but this is observed to be more common in adult female patients. The pathophysiology remains unclear, but it's thought to arise from disturbances between central and peripheral neural tissue in the perception of itch, causing that persistent itch-scratch cycle. Several psychological disturbances like anxiety and depression have been associated with this dermatological condition.

# Pathophysiology
- LSC develops over the regions which are accessible to scratching.
- The pathogenesis of LSC is unclear, but clinical lesions are due to severe paroxysmal pruritus. The physical and emotional component of the cause are well known, compared to genetic, vascular and neurogenic component.
- Skin with atopic dermatitis and atopic diathesis is most likely to develop lichenification.
- There could be a potential relationship between central and peripheral neural tissue and inflammatory mediators in the perception of itch, leading to changes underlying LSC.
- Emotional disturbances such as anxiety, depression and obsessive-compulsive disorder or other stressors contribute to itching in many cases. 
- Some studies tried to find genetic support to pathology of LSC. Like, Serotonin transporter (5HTT) gene polymorphism and dysfunction association to LSC .
- Transient receptor potential channel A1 (TRPA1) which is seen in skin, sensory neuron and other tissues has been associated with decreased expression in the lesions of LSC. 
- Long interspersed element-1 (LINE-1) pattern changes in epidermis of LSC was found in a study. 
- On microscopic histopathological analysis, LSC appears as a hyperkeratotic plaque, with parakeratosis, acanthosis, spongiosis, papillary dermal fibrosis with vertical streaking of collagen bundles, irregularly thickened rete edges, and pseudoepitheliomatous hyperplasia.
- Electron microscopy shows collagen fibers attached to and above lamina basalis.

# Causes
- The most common cause of LSC is emotional factors. Other causes of LSC include
Atopic dermatitis
Eczema
Mechanical trauma
Extremes of temperature/humidity
Scars
Xerosis
Psoriasis
Insect bites
Lithium 
P-phenylenediamine (PPD) 
- Atopic dermatitis
- Eczema
- Mechanical trauma
- Extremes of temperature/humidity
- Scars
- Xerosis
- Psoriasis
- Insect bites
- Lithium 
- P-phenylenediamine (PPD) 

# Differentiating Lichen simplex chronicus from other Diseases
- Lichen simplex chronicus (LSC) must be differentiated from other diseases that cause thickened skin lesions such as:
- Atopic dermatitis
- Contact allergic dermatitis
- Tinea, candida and other fungal infections
- Lichen planus
- Psoriasis
- Mycosis fungoides
- Squamous cell carcinoma and others.

# Epidemiology and Demographics
- LSC has been estimated to occur among 12% of the people around the world.

## Age
- LSC is more commonly observed among patients aged 30 to 50 years old.

## Gender
- LSC is more commonly affected to females than males.
- The female to male ratio is approximately 2:1.

## Race
- Previous studies in past have shown LSC more common in African Americans and Asians.

# Natural History, Complications and Prognosis
- Prognosis is generally good with treatment, but some become persistent lesions.
- Special association with erectile dysfunction is seen in some studies.
- Some cases of malignant transformation of the lesion into squamous cell carcinoma or verrucous carcinoma is seen.

# Diagnosis

## History and Symptoms
- Diagnosis of LSC includes physical exams, history, and dermoscopy. The most common symptom is Itching.
- LSC mostly occurs in easy to reach areas like the head, neck, extensor sides of forearm, scalp, vulva, pubis, and scrotum. It can occur as a single or multiple lesions.
- Itching usually occurs in the nighttime, and it's mostly absent when active.

## Physical Examination
- Lesions appear erythematous, scaly, well-demarcated, rough plaques eventually turning into thickened and hyperpigmented due to chronic pruritus.
- These plaques can vary in size from 3 by 6 centimeters to 6 by 10 centimeters. The color of the lesion varies according to the stage of the lesion.

## Laboratory Findings
- There are no specific laboratory findings associated with LSC.
- You can do few tests to identify the stressor behind the disease like serum IgE levels to support underlying atopy.

## Other Diagnostic Studies
- Patch test can exclude possible allergic contact dermatitis as a cause of disease.
- Potassium hydroxide examination and fungal cultures help to eliminate tinea cruris and candidal infections, especially when the lesions are involved with genitals.
- Skin biopsies may be performed to exclude psoriasis or mycosis fungoides.

# Treatment

## Medical Therapy
- The mainstay of therapy for LSC is to reduce pruritus and support the lesion and body to heal.
- Topical anti-inflammatory therapy like corticosteroids, topical emollients, anti-histamines, and antibiotics if suspicion of secondary infection.
- Corticosteroids decreases the inflammation, and also improve the lesion hyperkeratosis.
- Depending on the size, extent and location of lesion, choice of corticosteroid (mild or high potent topical preparations) is made.
- Intralesional steroid injections are used for refractory cases.
- Occlusion has been observed to improve the treatment effectiveness. Also, it prevents from scratching. 
- Psychological treatment, such as psychotherapy, as well as drugs like anti-anxiety medications are found to be effective, because of the emotional factors of the disease.
- Other treatments like doxepin and capsaicin, aspirin/dichloromethane, immunomodulators like tacrolimus and pimecrolimus, and injections of botulinum toxins. 

## Surgical/ Other therapy
- Cryosurgery, Phototherapy, Photochemotherapy and Transcutaneous Electrical Nerve Stimulation have been studied in cases not responsive to any of the medical therapy. 

## Prevention
- Effective measures for the primary prevention of LSC include helping patients to minimize scratching on an individual basis. Treating the underlying mental disorder if it's involved in the etiology of disease.