A patient with well‑defined erythematous plaques, hair loss, partially adherent scales and a positive carpet‑tack sign on the scalp—what is the most appropriate next step in diagnosis and management?

Discoid Lupus Erythematosus: Diagnosis and Management

The carpet-tack sign (follicular keratotic plugs adherent to the undersurface of removed scales) is pathognomonic for discoid lupus erythematosus (DLE), and when present alongside well-defined erythematous plaques, hair loss, and partially adherent scales on the scalp, the next step is to perform dermoscopy to confirm characteristic features, followed by scalp biopsy for histopathological confirmation before initiating immunosuppressive therapy. 1, 2

Diagnostic Approach

Clinical Recognition

• Follicular keratotic plugs visible on dermoscopy correlate with hyperkeratosis and plugging of follicular ostia with keratotic material, and their presence alone or with other dermoscopic features enables timely diagnosis 1
• The carpet-tack sign (also called "tin-tack sign") appears as small horny plugs attached to the undersurface of scales removed from affected sites and is characteristic of DLE, though rarely can occur in localized pemphigus foliaceus 3
• DLE manifests as scaly indurated plaques with erythema and peripheral hyperpigmentation, often affecting sun-exposed sites including the scalp 2

Dermoscopic Examination

• Follicular keratotic plugs (60.8% of cases) and perifollicular whitish halos (54.1%) are the most commonly detected dermoscopic criteria in DLE 2
• Early-stage lesions demonstrate follicular keratotic plugs and perifollicular white halos on dermoscopy 2, 4
• Late-stage lesions show telangiectasia and white structureless areas, indicating disease progression and scarring 2, 4
• Additional dermoscopic features include blue-gray and brown dots, follicular red dots, white rosettes, and white areas 2
• Perfect agreement exists between dermoscopic follicular plugs and histopathological findings, making dermoscopy a reliable activity assessment tool 2

Histopathological Confirmation

• Scalp biopsy is mandatory when DLE is suspected based on clinical and dermoscopic findings to confirm the diagnosis before starting immunosuppressive treatment 5, 2
• Characteristic histopathological features include interface dermatitis, peri-appendageal infiltrate, melanin incontinence, melanophages, and fibrosis 2
• Dermoscopic patterns correlate well with histopathological changes, allowing dermoscopy to assess lesion activity 2, 6

Differential Diagnosis to Exclude

Scalp-Specific Conditions

• Tinea capitis would demonstrate scaling, inflammation, or hair loss with positive fungal culture; perform fungal culture only when inflammation or scaling suggests infection 5, 7
• Alopecia areata shows exclamation-mark hairs and yellow dots on dermoscopy without follicular keratotic plugs 8, 9
• Kerion (inflammatory tinea capitis) presents as painful, boggy inflammatory masses studded with pustules, unlike the indurated plaques of DLE 5

Other Inflammatory Dermatoses

• Seborrheic dermatitis presents with greasy yellowish scaling rather than adherent scales with follicular plugs 5
• Psoriasis demonstrates characteristic silvery scales without the carpet-tack sign 5
• Lichen planopilaris (scarring alopecia) requires biopsy to differentiate from DLE when scarring is present 5

Management Algorithm

Initial Treatment Considerations

• Systemic lupus erythematosus (SLE) develops in a minority of DLE cases; therefore, evaluate for systemic features including arthralgia, photosensitivity, facial rash, and order lupus serology (ANA, anti-dsDNA, complement levels) 5, 2
• Topical corticosteroids are first-line for localized DLE lesions, though potent formulations lack convincing evidence in scalp disease 9
• Antimalarial drugs (hydroxychloroquine) are standard systemic therapy for extensive or refractory DLE, with ophthalmologic monitoring required due to retinopathy risk (0.5% incidence) in patients >60 years or with treatment duration >5 years 5

Refractory Disease

• Anifrolumab (type I interferon receptor antagonist) demonstrates efficacy in severe, treatment-refractory DLE with SLE, inducing clinical, dermoscopic, and histological remission 6
• Dermoscopy serves as a valuable follow-up tool to monitor therapeutic response, tracking regression of follicular plugs and scarring areas 6

Monitoring and Follow-Up

• Repeat dermoscopy at follow-up visits to assess disease activity: persistence of follicular plugs indicates active disease, while their resolution suggests treatment response 2, 6
• Repeat biopsy is recommended if clinical morphology changes or if there is lack of response to treatment 5
• Assess for scarring alopecia development, as DLE can cause permanent hair loss requiring early aggressive treatment 5

Critical Pitfalls to Avoid

• Do not delay biopsy when DLE is suspected; histopathological confirmation is essential before initiating immunosuppressive therapy that may have significant adverse effects 2
• Do not confuse the carpet-tack sign with simple scaling; the pathognomonic feature is the adherent keratotic plugs on the undersurface of removed scales, not just surface scaling 1, 3
• Do not overlook systemic evaluation; order lupus serology when systemic features (joint pain, photosensitivity, facial rash) accompany scalp lesions 5, 8
• Do not empirically treat with antifungals when scaling or hair loss patterns are inconsistent with tinea capitis; fungal culture is indicated only when inflammation or scaling suggests infection 5, 7
• Do not order extensive autoimmune panels for isolated scalp DLE without systemic features, as this wastes resources without changing management 8, 9

Psychosocial Considerations

• Scarring alopecia from DLE profoundly affects quality of life; address psychological impact and consider mental health referral for patients experiencing depression, social withdrawal, or work difficulties 5, 9
• Wigs provide immediate cosmetic benefit for patients with extensive scarring alopecia from longstanding DLE 9