Linear Lichen Planus ICD-10: L43.9

Inflammatory skin condition / Lichen planus variant

Often searched as: purple rash in a line on arm, linear rash on skin, rash after scratching skin, rash that follows a scratch line, purple flat bumps in a row, itchy line rash on leg, linear skin condition, rash that appeared after injury…

Clinical urgency level

lowmediumhigh

Systems Affected

skin

Severity Levels

mild

A single linear band of flat purple papules on a limb, stable, mildly itchy — manageable with topical corticosteroids.

moderate

Multiple or expanding linear lesions, significant itch, affecting visible areas — requires dermatologist evaluation and systemic or potent topical treatment.

severe

Extensive linear lesions spreading across large areas, very symptomatic, or involving mucous membranes — requires specialist management.

Red Flags

Lesion rapidly expanding along a limb or following a new scratch line
Strong itching or burning interfering with sleep or daily life
Purple or dark linear rash appearing on a child with no clear cause
Lesion changing color, becoming raised, or developing ulceration
Linear rash involving the mouth or genitals alongside skin lesions

Clinical Presentation

Linear lichen planus — violaceous papules in a band on the forearm

View gallery on DermNet NZ (image gallery reference)

Classic lichen planus papules — flat-topped violet papules

Source: Wikimedia Commons (CC BY-SA 3.0 )

When to See a Doctor

See a dermatologist if you notice a purple or brownish rash arranged in a line on your arm or leg, especially if it appeared after a scratch or injury, or if it's itchy and not improving. Linear rashes can mimic other conditions (like linear psoriasis or epidermal nevi) and need a professional eye for accurate diagnosis.

Differential Diagnosis

Linear psoriasis
Epidermal nevus (linear, present from birth or childhood)
Linear morphea (linear scleroderma)
Lichen striatus (mainly in children — self-resolving)
Linear Darier disease
Contact dermatitis (linear from plant or allergen exposure)
Koebnerized eczema

Comorbidities

Classic lichen planus (may co-exist)
Hepatitis C infection (associated with lichen planus broadly)
Other autoimmune conditions
Emotional stress (known trigger for lichen planus flares)

Prognosis

Linear lichen planus is generally benign and often self-limiting, resolving within months to a few years. However, post-inflammatory hyperpigmentation (dark marks) can persist long after the active lesions clear, especially in darker skin tones. It does not carry a risk of malignant transformation. Topical corticosteroids and calcineurin inhibitors are effective for symptom control. Recurrence after resolution is possible but not the rule.

Detailed Overview

Causes, Symptoms, and When to Take Action Linear lichen planus is a variant of lichen planus that presents with lesions arranged in a line or band-like pattern, often following trauma to the skin. It is a form of the broader condition lichen planus, with similar underlying processes but distinct appearance. How It Looks Texture: Flat-topped, firm papules or plaques, sometimes with scaliness Color: Violaceous (purpleish), red, or brownish depending on skin tone Shape: Papules or plaques arranged in a linear or band-like pattern; lesions may follow lines of trauma Location: Typically on limbs or areas where skin has been scratched or injured Why Does It Appear? Appears as a manifestation of the same inflammatory reaction seen in lichen planus Triggered often by trauma or skin injury (Koebner phenomenon) which causes lesions along scratch or injury lines Other contributing factors include immune dysregulation, genetic predisposition, and possibly exposure to cause antigens Should You Be Concerned? Linear lichen planus is benign. However, concern is needed if: The lesion changes in size, color, or shape It becomes symptomatic (strong itching, pain) The involvement is extensive or persistent Early evaluation helps distinguish it from other linear dermatoses and prevents misdiagnosis. Can You Prevent It? Prevention isn't fully possible. But risk reduction may include: Avoid unnecessary trauma to skin Attend to minor injuries promptly Monitor skin for early signs especially after injury 👉 How Piel AI Can Help Piel AI can help you monitor linear lesions over time via regular imaging. While it is not diagnostic, it assists in noting changes in pattern, spread, or severity, and supports consultation with dermatology professionals. Summary Linear lichen planus is a variant where lesions appear in lines or bands, often after skin injury. It has the same underlying type of inflammation as other forms of lichen planus. While benign, changes in lesions or symptoms should prompt evaluation. Monitoring and minimizing trauma to the skin help manage the condition.

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