What’s causing this woman’s chronic rash on her ankles, feet and wrists?

Clinical features

• Presentation:
  • Flat-topped, polygonal, violaceous papules with fine white lines on the surface (Wickham striae).
  • Often symmetrical and may be pruritic or painful, especially with mucosal involvement.
  • Chronic, relapsing course; new lesions may develop over weeks to months.

• Symptoms:
  • Pruritus is common, particularly in cutaneous forms.
  • Oral lesions may cause soreness, especially with spicy or acidic foods.
  • Nail involvement may lead to thinning, ridging or even permanent loss.
  • Scalp involvement (lichen planopilaris): may cause scarring alopecia.

• Affected areas:
  • Wrists, ankles, lower back and shins are common sites.
  • Oral mucosa (buccal surfaces) frequently affected, often bilateral.
  • Genital involvement (glans penis, vulva) may present with pain or erosions.
  • Scalp and nails may be affected in more severe or disseminated disease.

Epidemiology

• Most commonly affects those aged 30–60 years.
• Slight female predominance in mucosal and genital forms.

Diagnosis

• Clinical evaluation:
  • Diagnosis is usually clinical, based on appearance and distribution of lesions.
  • Examine skin, mouth, nails, scalp and genitals systematically.
  • Take a thorough medication history.

• Investigations:
  • Skin biopsy: Consider if diagnosis is uncertain or to exclude differential diagnoses (eg, lupus, GVHD, drug reaction).
  • Oral swab: For candidiasis if erosive lesions are present.

Differential diagnosis

• Psoriasis: silvery scale, more extensor involvement, often nail pitting, less itchy.
• Discoid lupus erythematosus: well-demarcated plaques, often photosensitive.
• Lichenoid drug eruption: similar histology but more widespread, less pruritic.
• Oral candidiasis: white patches may be confused with Wickham striae.
• Leukoplakia or SCC: in persistent or ulcerated oral lesions.

Red flags

• Erosive oral or genital lesions: risk of secondary infection and significant discomfort.
• Scalp involvement: risk of scarring alopecia – refer early.
• Persistent oral lesions: small but real risk of malignant transformation (especially in erosive form).
• Widespread or atypical lesions: may suggest systemic disease or drug-induced lichenoid reaction.

Management

• First-line (mild to moderate cutaneous):
  • Topical corticosteroids: potent (eg, betamethasone) or very potent (eg, clobetasol) applied once daily.
  • Antihistamines: for itch relief.
  • Emollients for barrier support.

• Mucosal/genital:
  • Topical corticosteroids: eg, betamethasone mouthwash (unlicensed).
  • Topical tacrolimus (unlicensed) may be considered for resistant mucosal disease.
  • Maintain oral hygiene and avoid irritants (eg, alcohol-based mouthwash).

• Nail or scalp involvement:
  • Refer to dermatology.
  • Intralesional steroids or systemic treatment may be required.

• Severe or refractory disease:
  • Systemic therapies: eg, acitretin, methotrexate or hydroxychloroquine – specialist initiation.
  • Dermatology referral is usually appropriate for widespread or persistent disease.

Patient education

• Understanding the condition:
  • Lichen planus is a chronic inflammatory condition; not infectious or cancerous.
  • May resolve spontaneously over 1–2 years, though oral and genital forms can persist longer.

• Triggers and associations:
  • Discuss any potential drug-related causes.
  • Highlight importance of good oral/genital care and follow-up in persistent mucosal disease.

• When to refer:
  • Scalp, nail or erosive mucosal/genital involvement.
  • Suspected malignant transformation in longstanding oral lesions.
  • Diagnostic uncertainty or poor response to first-line treatment.