Lichen striatus
Synonyms and keywords: Linear lichenoid dermatosis

# Overview
Lichens striatus (LS) is an acquired, self-limiting inflammatory dermatosis that follows the lines of Blaschko.

# Pathophysiology
Blaschko lines have an embryologic origin and correspond to the direction of growth of the cutaneous cells, resulting in a cutaneous mosaicism. The genetic mosaicism could be responsible for cutaneous antigenic mosaicism,  the expression of which might be induced by various external factors. Lichen striatus has been considered to be the consequence of an acquired stimulus that induces a loss of immunotolerance to embryologically abnormal clones, resulting in a T-cell-mediated inflammatory reaction.

# Causes
The etiology of the eruption is unknown. Several theories suggest a genetic predispostion with the following acting as possible triggers.
- Hypersensitivity
- Cutaneous injury
- Viral infection
- Environmental factors
- Immunization
- Pregnancy

# Differentiating Lichen Striatus from other Conditions
- Lichen planus

# Epidemiology and Demographics
Lichen striatus is a rare skin condition that is seen primarily in children, most frequently appearing ages 515. It consists of a self-limiting eruption of small, scaly papules.

# Natural History, Prognosis and Complications
Lichen striatus has spontaneous remission, although the course of the disease is prolonged when nail involvement exists. Patients treated by a combination of topical retinoid with topical steroid have rapid resolution of lichen striatus and they not only achieve satisfying cosmesis, but also complete resolution of their pruritus. The most common side effect of the topical medication is localized irritation at treatment sites, but most of them would tolerate the treatment well.

# Diagnosis

## History and Symptoms
Lichen striatus presents as an eruption characterized by sudden onset of flat-topped, 1 to 4 mm, pink, tan, or hypopigmented papules in a linear configuration or Blaschkoid distribution. It may be associated with some irritation and soreness in the muscles of the affected parts.

## Physical Examination

### Skin
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.
- Lichen striatus. Adapted from Dermatology Atlas.

## Laboratory Findings
Histopathologic examination of papules would reveal the presence of a lichenoid, lymphocytic infiltration and scattered melanin incontinence in the papillary dermis with epidermal hyperkeratosis, exocytosis of lymphocytes and necrotic keratinocytes.

# Treatment
The condition is benign and no need for biopsy. Studies have showed monitoring without biopsy is a reasonable approach to the management of uncomplicated lichen striatus, particularly when the face is involved. However topical medications would produce rapid resolution. The following are currently used medications :
- Topical retinoids
- Topical steroids
- Tacrolimus, especially for facial lesions
- Photodynamic theraphy