How is discoid lupus erythematosus diagnosed?

Diagnosis of Discoid Lupus Erythematosus

Discoid lupus erythematosus is diagnosed through skin biopsy with histopathological examination, which is mandatory for confirmation, and should be complemented by direct immunofluorescence testing and baseline autoantibody screening to assess for systemic involvement. 1, 2

Clinical Recognition

The diagnosis begins with identifying characteristic skin lesions:

• Well-demarcated discoid erythematous plaques with firmly adherent scales or crusts, central atrophy, scarring, and pigmentary changes 2
• Predilection for sun-exposed areas: scalp, face (81.1% of cases), auricle, lips, limbs (71.7%), and upper body 2, 3
• Photosensitivity is a hallmark feature, with ultraviolet radiation exposure being the most frequent triggering factor (86.8% of cases) 3
• Lesions may lead to irreversible scarring alopecia when involving the scalp 2

Mandatory Skin Biopsy

A skin biopsy is required for histopathological analysis to confirm the diagnosis and must be repeated if clinical morphology changes or treatment fails 4, 1:

Histopathological Features

• Hyperkeratosis and follicular plugging 2, 3
• Focal epidermal thinning with vacuolar alteration of the dermo-epidermal interface 2
• Thickening of the epidermal basement membrane 2
• Superficial and deep perivascular and periadnexal lymphocytic infiltrate, often with interstitial mucin 2
• Interface dermatitis with basal cell vacuolization 3, 5

Direct Immunofluorescence (DIF)

• Deposits of immunoglobulins (IgM and IgG) and complement at the dermo-epidermal junction 2, 3
• IgG deposition pattern is the most important immunohistochemical feature for diagnosis, with greater diagnostic specificity than histopathology alone 6
• The combination of histopathology and immunofluorescence provides the most reliable diagnostic results 6

Baseline Laboratory Evaluation

Comprehensive autoantibody testing and laboratory screening are essential to exclude systemic lupus erythematosus and assess disease extent 7, 1:

Autoantibody Panel

• ANA (antinuclear antibody) - positive in 56.6% of DLE cases 3
• Anti-dsDNA antibodies - positive in 45.3% of DLE cases 3
• Anti-Ro/SSA and anti-La/SSB antibodies - provide prognostic information 4, 1
• Anti-RNP, anti-Sm antibodies 1
• Antiphospholipid antibodies 1
• Complement levels (C3 and C4) to assess for systemic involvement 7, 1

Routine Laboratory Tests

• Complete blood count (CBC) to identify cytopenias (anemia, thrombocytopenia, leukopenia) 4, 1
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) 1
• Serum creatinine and serum albumin 1
• Urinalysis with urine protein-to-creatinine ratio to screen for renal involvement 4, 1

Dermoscopic Assessment

Dermoscopy can aid in early diagnosis and disease activity assessment, particularly in skin of color 5, 8:

• Follicular keratotic plugs (60.8% of cases) with perfect agreement with histopathology 5
• Perifollicular whitish halo (54.1% of cases) 5
• Arborizing blood vessels (85.7% of cases) 8
• Starburst pattern - radial arrangement of arborizing vessels between radially arranged perifollicular whitish halos (39.3% of cases) 8
• White rosettes (57.1% of cases) 8
• Pigmentation (82.1% of cases) 8

Disease Activity Monitoring

The Cutaneous Lupus Disease Area and Severity Index (CLASI) should be used at each visit to quantify skin disease activity and damage 4, 1

Critical Diagnostic Pitfalls

• Do not rely solely on ANA testing, as it can be positive in other conditions and is only positive in approximately half of DLE cases 1, 3
• Repeat biopsy is mandatory when clinical morphology changes or when there is inadequate response to therapy 4, 1
• Markedly elevated CRP (>50 mg/L) should trigger investigation for superimposed bacterial infection, as lupus activity alone rarely produces such high levels 1
• Regular monitoring for systemic involvement is essential, as some patients can develop serious organ-threatening disease including lupus nephritis 7