Discoid Lupus Erythematosus

Discoid lupus erythematosus (DLE) is a chronic autoimmune skin condition that causes inflamed, disc-shaped (round or oval) patches on the skin. These patches typically appear on sun-exposed areas — the face, ears, and scalp — and heal with permanent scarring, loss of skin colour, and hair loss. DLE is the most common form of chronic cutaneous lupus erythematosus and is distinct from systemic lupus erythematosus (SLE), though a small proportion of patients may eventually develop systemic disease.

DLE can affect anyone, but certain groups are more frequently affected.

• Prevalence: Approximately 6.5 per 100,000 people
• Age: Most commonly diagnosed between 20 and 40 years of age
• Sex: Women are affected 2–3 times more often than men
• Ethnicity: Significantly more common in people of African descent, who also tend to have more severe disease with greater scarring, pigmentary changes, and scalp involvement
• Risk factors: Sun exposure (ultraviolet light is the main trigger), smoking (worsens the disease and reduces treatment effectiveness), family history of autoimmune conditions

DLE typically presents as well-defined, round or oval patches on sun-exposed skin.

• Active lesions: Red or violaceous (purple-red) patches with adherent scale; when the scale is peeled off, small keratotic spines are visible on its undersurface (the "carpet tack sign")
• Follicular plugging: Visible filling of hair follicle openings with keratotic material, giving the skin a rough texture
• Scarring: As lesions heal, the centre becomes pale, atrophic (thinned), and depressed, with visible small blood vessels (telangiectasia)
• Pigmentary changes: Darkening (hyperpigmentation) at the active edges and lightening (hypopigmentation or depigmentation) in the centre — especially noticeable in darker skin types
• Scalp involvement: Causes permanent scarring hair loss (cicatricial alopecia); the affected areas are smooth, pale, and devoid of hair follicle openings
• Common locations: Face (cheeks, nose, ears), scalp, neck; less frequently on hands, arms, and trunk

Two patterns are recognized:

• Localized DLE (~80%): Lesions limited to the head and neck
• Generalized DLE (~20%): Lesions both above and below the neck; carries a higher risk of progression to systemic lupus

DLE is an autoimmune condition in which the immune system attacks the skin's own cells, particularly at the junction between the outer skin layer (epidermis) and the deeper layer (dermis).

• UV light trigger: Sunlight is the main environmental trigger; UV radiation damages skin cells, causing them to release proteins that activate the immune system
• Immune dysregulation: The body produces an excessive inflammatory response dominated by interferon (a type of immune signalling molecule), which sustains chronic inflammation
• Genetic predisposition: There is a familial tendency; certain gene variants involved in immune regulation increase susceptibility
• Smoking: A significant aggravating factor that worsens disease activity and reduces the effectiveness of antimalarial medications

Diagnosis is based on the characteristic clinical appearance, confirmed by skin biopsy.

• Clinical examination: Well-defined, disc-shaped plaques with scale, follicular plugging, scarring, and pigmentary changes in a sun-exposed distribution
• Dermoscopy: Reveals follicular keratotic plugs, white structureless areas, branching (arborizing) vessels, and speckled brown pigmentation
• Skin biopsy: Shows interface dermatitis (inflammation at the junction between epidermis and dermis), follicular plugging, thickening of the basement membrane, and mucin deposits in the dermis
• Direct immunofluorescence (lupus band test): Demonstrates a band of immunoglobulin and complement deposits at the dermal-epidermal junction; in DLE, positive only in lesional skin
• Blood tests: ANA (antinuclear antibodies) is positive in approximately 20–30% of patients with skin-limited DLE; full blood count, renal function, and urinalysis are checked to screen for systemic lupus

Treatment aims to control inflammation, prevent new lesions, and minimize scarring. Early treatment is essential — once scarring occurs, it is permanent.

Sun protection (essential for all patients):

• Broad-spectrum sunscreen (SPF 50+) applied daily, reapplied every 2 hours when outdoors
• Protective clothing, wide-brimmed hats, avoidance of peak sun hours
• Smoking cessation — smoking reduces the effectiveness of treatment

For localized disease:

• High-potency topical corticosteroids (clobetasol propionate 0.05%) applied to active lesions
• Topical calcineurin inhibitors (tacrolimus 0.1%) — preferred for facial lesions to avoid skin thinning from corticosteroids
• Intralesional corticosteroid injections (triamcinolone acetonide 3–5 mg/mL) for resistant plaques

For widespread or resistant disease:

• Hydroxychloroquine 200–400 mg daily — the mainstay systemic treatment; may take 2–3 months for full effect
• Methotrexate 10–25 mg weekly — for patients who do not respond to hydroxychloroquine
• Other options for refractory cases: mycophenolate mofetil, thalidomide, retinoids

Prognosis: DLE is a chronic condition that tends to wax and wane, often worsening with sun exposure. With consistent treatment and sun protection, most patients achieve good disease control. However, scarring and pigmentary changes are permanent. Approximately 5% of patients with localized DLE may develop systemic lupus erythematosus, rising to up to 20–28% in generalized DLE.

• DLE is not contagious — it is an autoimmune condition
• Sun protection is the single most important measure you can take to prevent flares
• Smoking significantly worsens the disease — cessation is strongly recommended
• Early treatment prevents permanent scarring and hair loss
• When to seek medical attention: New or expanding patches; any non-healing ulcer or nodule within an old scar (small risk of skin cancer in longstanding lesions); joint pain, fatigue, or mouth ulcers that could suggest systemic lupus
• Regular follow-up with a dermatologist is important to monitor disease activity and screen for systemic involvement
• There is a small but real risk (2–3%) of squamous cell carcinoma developing in chronic, longstanding DLE scars — report any new growth or ulceration in an old lesion

• Incidence: 0.8–1.3 per 100,000 person-years (Manhattan Lupus Surveillance Program)
• Prevalence: 6.5–9.0 per 100,000 (Manhattan data); broader CLE prevalence 30–86 per 100,000 (New Zealand study, Jarrett et al., 2016)
• Demographics: F:M ratio approximately 2–3:1; peak onset in the 4th–5th decades. DLE represents ~80% of all chronic cutaneous lupus erythematosus
• Racial disparities: Prevalence in non-Latino Black patients is 23.5/100,000 versus 1.8/100,000 in non-Latino Whites (13-fold disparity). Black patients show worse CLASI damage scores, greater odds of scalp involvement (OR 2.54), ear involvement (OR 1.97), dyspigmentation (OR 48.9), and scarring alopecia (OR 3.00) (Joseph et al., 2021)
• Paediatric DLE: Mean age at onset ~8.9 years for DLE-only; 37–41% may meet SLE criteria at baseline (Ezeh et al., 2022)
• Modifying factors: Smoking is a strong exacerbating factor and reduces antimalarial efficacy. Socioeconomic deprivation (area deprivation index >5) is independently associated with 4-fold greater odds of moderate-to-severe damage (Faden et al., 2024)

Genetic Susceptibility

• Susceptibility genes: TYK2, IRF5, CTLA4, HLA associations
• Rare monogenic forms (familial chilblain lupus) with mutations in nucleic acid-handling enzymes (TREX1, SAMHD1, ADAR1), enhancing type I interferon signalling
• Familial clustering supports a polygenic model in most cases

UV Radiation as Environmental Trigger

• UV irradiation is the primary environmental trigger
• Induces keratinocyte apoptosis, exposing nuclear autoantigens (DNA, RNA, histones)
• Triggers type I IFN-dominated inflammatory response via activation of plasmacytoid dendritic cells (pDCs)
• Symptom onset may occur up to 3 weeks after UV exposure (delayed photosensitivity)

Type I Interferon Pathway

• Central pathogenic role: nucleic acid sensors (TLR7, TLR9, cGAS-STING) recognize self DNA/RNA released from apoptotic cells
• Activated pDCs produce IFN-α, creating a positive feedback loop sustaining autoimmunity
• IFN signature is detectable in lesional skin and drives recruitment of cytotoxic T cells
• This pathway is the therapeutic target of anifrolumab (anti-IFNAR1) and deucravacitinib (TYK2 inhibitor)

Immune Mechanisms

• Interface dermatitis: cytotoxic CD8+ T lymphocytes attack basal keratinocytes
• Immune complex deposition at the dermal-epidermal junction activates complement (classical pathway)
• Th1-biased cutaneous infiltrate
• Defective clearance of apoptotic cells and nucleic acid debris amplifies autoimmune activation

Classic DLE

• Well-defined, coin-shaped erythematous plaques with adherent scale
• Follicular hyperkeratosis with the "carpet tack sign" (keratotic spines on undersurface of removed scale)
• Active margins: erythema, hyperpigmentation
• Central changes: atrophy, depigmentation, telangiectasia, scarring
• Preferential distribution: face (malar region, nose, ears), scalp, neck, dorsal hands
• Three concentric zones in classic lesions (Petrescu): erythematous periphery, keratotic intermediate zone, atrophic-cicatricial centre

Localized vs. Generalized DLE

• Localized (~80%): lesions limited to the head and neck; 1–5% progress to SLE
• Generalized (~20%): lesions above and below the neck; up to 20–28% may progress to SLE

Scalp DLE

• One of the most common and impactful manifestations
• Causes permanent cicatricial alopecia with follicular destruction
• Presents with perifollicular erythema, follicular plugging, scaling, progressing to smooth atrophic scars
• More severe in Black patients: earlier onset, greater extent, worse scarring
• Trichoscopy: follicular keratotic plugs, large yellow dots, arborizing vessels, white structureless areas, absent follicular openings

Variants

• Hypertrophic/verrucous DLE (~2%): thick, warty plaques mimicking SCC or hypertrophic lichen planus; most common on forearms, face, ears
• Mucosal DLE: lip involvement (erythematous/erosive plaques) most common; also buccal mucosa, palate, gingiva; lip DLE carries risk of SCC
• DLE-lupus panniculitis overlap: DLE lesions overlying deep subcutaneous nodules in ~70% of lupus panniculitis; lipoatrophy may result
• Chilblain lupus: pernio-like lesions on acral sites; may be monogenic (TREX1, SAMHD1 mutations)

Non-scalp DLE (dermoscopy):

• Follicular keratotic plugs (67%) — most characteristic finding
• White perifollicular halo (66%)
• White scale (40%)
• Speckled brown pigmentation (39%)
• White structureless areas (37%)
• Arborizing vessels (35%)

Scalp DLE (trichoscopy):

• White structureless areas (62%)
• Arborizing/branching vessels (58%)
• White scales (54%)
• Follicular keratotic plugs (47%) — large yellow dots on trichoscopy
• Absent follicular openings (46%)
• Perifollicular scaling (44%)
• Speckled brown pigmentation (38%)
• Fibrotic white dots (34%)

(Zychowska & Zychowska, 2020 — systematic review)

Distinguishing scalp DLE from LPP on trichoscopy:

• DLE: large yellow follicular plugs, arborizing vessels, speckled pigmentation, white structureless areas
• LPP: peripilar casts (cylindrical scales), blue-grey dots in target pattern, tufted follicles, perifollicular erythema without follicular plugging

Punch biopsy (4 mm) from an active, fully developed lesion. Both vertical and horizontal sections are informative.

Characteristic findings:

• Interface dermatitis: vacuolar degeneration of the basal layer with lymphohistiocytic infiltrate
• Follicular plugging (dilated follicular ostia filled with keratotic material)
• Basement membrane thickening (PAS-positive; best demonstrated on PAS stain)
• Dermal mucin deposition (Alcian blue or colloidal iron stain)
• Periadnexal and perivascular lymphocytic infiltrate extending into the deep dermis
• Hyperkeratosis (ortho- and/or parakeratotic)
• Epidermal atrophy (in chronic lesions)
• Melanin incontinence (pigmentary incontinence in dermis)

Distinguishing from LPP histologically:

• DLE: deeper and denser perivascular and periadnexal infiltrate, basement membrane thickening, mucin deposition, follicular plugging
• LPP: infiltrate concentrated at isthmus/infundibulum, concentric lamellar fibrosis, no mucin, no basement membrane thickening

Direct Immunofluorescence (Lupus Band Test)

• Granular deposition of IgG, IgM, IgA, and/or C3 at the dermal-epidermal junction
• Positive in ~75% of lesional DLE skin
• Key distinction: in DLE, LBT is positive only in lesional skin; in SLE, positive in both lesional and non-lesional skin (sun-exposed and sun-protected)
• Sensitivity for SLE diagnosis (on non-lesional skin): ~56.5%; specificity: ~88.2% (Wongtada et al., 2022)

CLASI Score

The Cutaneous Lupus Erythematosus Disease Area and Severity Index (CLASI) is the standard validated tool for quantifying:

• Activity score: erythema, scale/hypertrophy (13 anatomical sites)
• Damage score: dyspigmentation, scarring/atrophy, panniculitis, scalp scarring

Laboratory Workup

• ANA: positive in 20–30% of cutaneous-only DLE (vs. 95–100% in SLE)
• Anti-dsDNA: usually negative in cutaneous-only DLE
• CBC, renal function, urinalysis: baseline SLE screening
• Anti-Ro/SSA, anti-La/SSB: more relevant for SCLE
• Consider complement levels (C3, C4) if SLE suspected

Condition	Key Differentiating Features
Lichen planopilaris	Perifollicular erythema, peripilar casts, blue-grey dots; no follicular plugging; lamellar fibrosis on histology
Psoriasis	Silvery scale, Auspitz sign, nail pitting; no scarring; Munro microabscesses on biopsy
Actinic keratosis	Rough, sandpaper-like; no interface dermatitis; parakeratotic columns
Squamous cell carcinoma	Firm, indurated; may ulcerate; SCC can arise within chronic DLE
Seborrhoeic dermatitis	Greasy yellow scale; no scarring; spongiotic dermatitis on biopsy
Sarcoidosis	Non-caseating granulomas; apple-jelly nodules; no interface dermatitis
Tinea faciei	KOH-positive for fungal elements; annular with central clearing
Dermatomyositis	Heliotrope rash, Gottron papules; proximal muscle weakness
Morphoea	Sclerotic plaques; no follicular plugging; collagen deposition without interface dermatitis

Non-Pharmacological (All Patients)

• Photoprotection: SPF ≥50 broad-spectrum (UVA+UVB) daily; physical blockers (zinc oxide, titanium dioxide); protective clothing, wide-brimmed hats; UV-filtering window films
• Smoking cessation: Critical — smoking worsens disease and reduces antimalarial efficacy
• Vitamin D supplementation: Annual screening recommended given necessary sun avoidance

First-Line: Topical and Intralesional

• Potent/superpotent topical corticosteroids (clobetasol 0.05%, betamethasone dipropionate): First-line for localized disease. Medium-potency for facial lesions. Improvement expected within 2 weeks.
• Topical calcineurin inhibitors (tacrolimus 0.1%, pimecrolimus 1%): Preferred for face and intertriginous areas; no risk of atrophy. Improvement in ~4 weeks.
• Intralesional triamcinolone acetonide 3–5 mg/mL: Injected 1 cm apart into resistant plaques; repeated every 3–4 weeks.

Second-Line: Systemic Antimalarials

• Hydroxychloroquine 200–400 mg/day (max 5 mg/kg/day real body weight): Mainstay systemic therapy for all CLE subtypes. Response assessed at 6–8 weeks; full effect may take 3–6 months. Monitor: annual ophthalmologic screening for retinal toxicity (AAO guidelines), CBC, LFTs.
• Chloroquine 250 mg/day: Alternative to HCQ; may be slightly more effective but carries higher risk of retinopathy.
• Quinacrine (mepacrine) 100 mg/day: Can be added to HCQ for refractory cases; no retinal toxicity. Combination therapy is more effective than monotherapy.

Third-Line: Refractory Disease

• Methotrexate 10–25 mg/week: Low-quality evidence supports efficacy (Cochrane review: RR 3.57 vs. placebo). Monitor: CBC, LFTs, renal function. Supplement with folic acid.
• Mycophenolate mofetil 1–3 g/day: Immunosuppressive; for cases refractory to antimalarials.
• Thalidomide 50–100 mg/day: Very effective (~90% complete/marked response) but limited by peripheral neuropathy, teratogenicity, thromboembolism; 71% relapse on discontinuation.
• Lenalidomide: Potentially as effective as thalidomide with fewer adverse effects.
• Retinoids (acitretin, isotretinoin): For hypertrophic/verrucous DLE variant.
• Dapsone: Particularly for bullous lupus.

Emerging Therapies

• Anifrolumab (anti-IFNAR1): Type I interferon receptor blocker; 60–70% achieved CLASI-50 at 1 year in TULIP trials. Case reports show benefit in refractory chronic DLE.
• Deucravacitinib (TYK2 inhibitor): ~60% achieved CLASI-50 at week 48; oral administration advantage.
• Litifilimab (anti-BDCA2): Targets plasmacytoid dendritic cells; Phase III trials ongoing.
• Enpatoran (TLR7/8 inhibitor): Phase II WILLOW trial: 91.3% achieved CLASI-50.

Treatment Algorithm

1. All patients: Strict photoprotection + smoking cessation + vitamin D screening
2. Mild/localized: Topical corticosteroids or calcineurin inhibitors ± intralesional triamcinolone
3. Moderate or progressive: Add hydroxychloroquine 200–400 mg/day; assess at 3 months
4. HCQ failure: Add quinacrine 100 mg/day, or switch to methotrexate 10–25 mg/week
5. Refractory: Mycophenolate, thalidomide/lenalidomide, or consider anifrolumab in eligible patients

Progression to Systemic Lupus Erythematosus

• Localized DLE: 1–5% progress to SLE
• Generalized DLE: up to 20–28% progression
• Risk factors: age <25 at diagnosis (OR 2.8), phototype V–VI (OR 2.7), ANA ≥1:320 (OR 15.0), generalized DLE, family history of rheumatic disease (Fredeau et al., 2022)
• Median time to progression: ~15 months (Elman et al., 2019)
• Screening: baseline and periodic ANA, anti-dsDNA, CBC, renal function, urinalysis

Skin of Colour

• Higher prevalence, earlier onset, more severe disease
• Greater scarring, dyspigmentation, and scalp involvement
• Dyspigmentation is often the most distressing feature for patients
• May require earlier systemic therapy

Paediatric

• DLE is rare in children; higher rate of SLE progression (30–37%)
• All paediatric patients should be systematically screened for SLE at diagnosis
• Treatment follows adult protocols at weight-adjusted doses

Pregnancy

• Hydroxychloroquine is considered safe and should be continued during pregnancy (prevents lupus flares)
• Methotrexate, mycophenolate, thalidomide are contraindicated

• SCC developing in longstanding DLE scars: approximately 2–3% of chronic lesions
• Mean latency: 15–30 years of chronic DLE
• Lip DLE carries particular risk of malignant transformation to SCC
• SCC arising in DLE tends to be clinically aggressive with higher risk of metastasis
• Any new nodule, ulceration, or change within a longstanding DLE lesion warrants biopsy
• Long-term surveillance is recommended for all patients with chronic DLE

• Natural history: Chronic, relapsing course; worsening with UV exposure; heals with permanent scarring
• With treatment: Good control achievable with consistent therapy; scarred areas do not recover
• Early treatment is critical: Prevents irreversible scarring, alopecia, and dyspigmentation
• Psychosocial impact: Significant — disfiguring scars, pigmentary changes, and hair loss affect self-esteem and quality of life, particularly in visible locations and darker skin types
• SLE risk: 5% (localized) to 20–28% (generalized) — lifelong monitoring required

• The "carpet tack sign" (keratotic spines on the undersurface of removed scale) is highly characteristic of DLE
• Always examine the ears — conchal bowl DLE is common and frequently missed
• Ask about smoking at every visit — smoking is the most modifiable risk factor and reduces antimalarial efficacy
• Sunscreen alone is insufficient — UVA passes through window glass and clouds; broad-spectrum protection and behavioural measures are essential
• Biopsy from the active inflammatory edge, not the scarred centre — the centre shows only non-specific fibrosis
• DLE on the lower lip is a premalignant condition — long-term surveillance is mandatory
• In Black patients, dyspigmentation may be more distressing than inflammation — address cosmetic concerns proactively
• Hydroxychloroquine takes 2–3 months for effect — counsel patients before they conclude it is ineffective
• Always screen for SLE (ANA, CBC, renal function, urinalysis) at baseline and periodically, especially in generalized DLE
• The presence of both localized and generalized DLE in the same patient changes risk stratification for SLE