What are the differential diagnoses for Lichen Planus?

Differential Diagnosis of Lichen Planus

The primary differential diagnoses for lichen planus include lichen sclerosus, psoriasis, lichenoid drug reactions, lichenoid contact lesions, graft-versus-host disease, leprosy (on the face), and in severe cases, cutaneous T-cell lymphoma (mycosis fungoides). 1, 2, 3

Key Distinguishing Features by Condition

Lichen Sclerosus

• Presents with porcelain-white papules and plaques (not violaceous/purple like lichen planus), often with areas of ecchymosis 4
• Predominantly affects anogenital areas and spares vaginal mucosa, whereas lichen planus can involve true mucosal surfaces 4
• Histologically shows epidermal thinning with hyperkeratosis and a band of homogenized collagen below the dermoepidermal junction, with lymphocytic infiltrate beneath (not at) the junction 1, 5
• Critical caveat: Some lichen sclerosus cases may have small focal areas where inflammatory infiltrate approaches the dermoepidermal junction similar to lichen planus, and complicated cases may show thickened epidermis rather than atrophy 1, 5

Psoriasis

• Shows well-demarcated erythematous plaques with silvery scale on extensor surfaces (elbows, knees), scalp, and nails 5
• Histologically demonstrates regular acanthosis with elongated rete ridges of uniform length (not irregular acanthosis) 5
• Parakeratosis is more confluent and associated with neutrophils in the stratum corneum (Munro microabscesses) 5
• Lacks the lichenoid band-like lymphocytic infiltrate at the dermoepidermal junction that characterizes lichen planus 5

Lichenoid Drug Reactions

• Clinically and histologically indistinguishable from idiopathic lichen planus 3, 6
• Requires detailed medication history; common culprits include thiazides, antimalarials, beta-blockers, NSAIDs, and ACE inhibitors 3, 6
• Diagnosis confirmed by empiric withdrawal of suspected drug, though this may be complicated by need for alternative therapy 3

Lichenoid Contact Lesions

• Occur at sites of contact with dental restorations (amalgam most common) or other allergens 3
• Lesions typically adjacent to or directly contacting the allergen source 3
• The value of patch testing remains controversial for confirming diagnosis 3

Graft-Versus-Host Disease (Oral Lichenoid Lesions)

• Occurs in bone marrow transplant recipients 3
• Has recognized association with malignancy, requiring more aggressive surveillance 3
• Clinical history of transplantation is key distinguishing feature 3

Leprosy (Facial Lesions)

• Affects cooler areas including face, ears, and extremities 2
• Sensory loss is pathognomonic: Test all facial lesions with light touch and pinprick—sensory loss confirms leprosy, not lichen planus 2
• Lacks Wickham striae and oral mucosal involvement typical of lichen planus 2
• Normal sensation is preserved in lichen planus with pruritus typically present 2

Mycosis Fungoides (Early Cutaneous T-Cell Lymphoma)

• Can show irregular acanthosis with parakeratosis and lichenoid infiltrate 5
• Presence of atypical lymphocytes on biopsy is the primary diagnostic clue 5
• Requires high index of suspicion in chronic, treatment-resistant cases 7

Diagnostic Algorithm

Clinical Examination

1. Identify classic lichen planus features: violaceous, polygonal, flat-topped papules with fine white lines (Wickham striae) on flexor surfaces of wrists, forearms, and legs 2, 4, 8
2. Examine oral mucosa: oral involvement is common in lichen planus but not typical in leprosy or lichen sclerosus 2
3. Check sensation in facial lesions: sensory loss indicates leprosy 2
4. Assess distribution: psoriasis favors extensor surfaces; lichen sclerosus predominantly anogenital 4, 5

Histopathologic Confirmation

• Biopsy is mandatory before initiating treatment for atypical presentations 2
• The lichenoid (band-like) lymphocytic infiltrate hugging the dermoepidermal junction is the hallmark distinguishing feature of lichen planus 5
• Look for Wickham striae using tangential lighting or dermoscopy—their presence strongly suggests lichen planus 2

History Taking

• Obtain complete medication list to identify potential drug-induced lichenoid reactions 3, 6
• Ask about bone marrow transplantation (graft-versus-host disease) 3
• Document dental work or contact with potential allergens for lichenoid contact lesions 3

Critical Pitfalls to Avoid

• Do not assume epidermal atrophy excludes lichen sclerosus: complicated cases may show acanthosis and carry higher risk of squamous cell carcinoma 1, 5
• Do not dismiss hypertrophic variants: hypertrophic lichen planus on lower extremities can mimic premalignant lesions and requires biopsy 7
• Do not overlook malignant transformation: erosive mucosal lichen planus requires periodic follow-up due to controversial but possible premalignant potential 3
• Do not confuse signs of sexual abuse with lichen sclerosus in children, though trauma may trigger disease onset 1