What is the most likely diagnosis and appropriate work‑up for a patient with a facial rash confined to the bilateral cheeks, nasal folds, and chin and an isolated elevated rheumatoid factor?

Facial Rash with Isolated Elevated Rheumatoid Factor: Diagnosis and Work-Up

The most likely diagnosis is cutaneous lupus erythematosus (CLE), and you must obtain a skin biopsy for histopathological confirmation as the gold standard diagnostic test. 1, 2

Why Cutaneous Lupus is Most Likely

The distribution pattern—bilateral cheeks, nasal folds, and chin—is characteristic of lupus-specific cutaneous manifestations, even though it spares the classic "butterfly" distribution. 3, 4 Importantly:

• Isolated elevated RF is a red herring. RF positivity occurs in only 9% of checkpoint inhibitor-associated sicca syndrome and is rarely positive in lupus-associated vasculitis. 5 RF alone does not establish rheumatoid arthritis without clinical arthritis and anti-CCP antibodies.
• Facial rashes involving the cheeks and nasal folds are well-documented presentations of SLE and CLE, including unilateral or atypical distributions that can mimic other dermatoses. 3, 6

Mandatory First Step: Skin Biopsy

You must perform a skin biopsy before proceeding with further work-up. 1, 2

• Use either complete excision of small lesions or an incisional biopsy (spindle-shaped or punch biopsy of at least 4 mm) to capture both superficial and deep dermal changes. 2
• Histopathological confirmation is mandatory because many inflammatory and infectious disorders mimic lupus clinically. 2
• Repeat biopsy is required if clinical morphology changes or treatment fails. 1, 2

Essential Serologic Evaluation

Once biopsy is obtained, order the following autoantibody panel simultaneously:

• ANA (antinuclear antibody) is the primary screening tool for SLE and connective tissue diseases. 1
• Anti-dsDNA antibodies correlate with SLE disease activity and renal involvement. 7, 1
• Anti-Ro/SSA and anti-La/SSB antibodies are essential for evaluating sicca syndrome (dry eyes/mouth) and provide prognostic information. 7, 1
• Complement C3 and C4 levels are associated with active SLE and help monitor disease flares. 7, 1
• Antiphospholipid antibodies require repeat testing at 12 weeks to confirm persistent positivity if initially positive. 1

Baseline Laboratory Assessment

Order these tests to identify systemic involvement and exclude mimics:

• Complete blood count with differential to identify cytopenias (anemia, thrombocytopenia, leukopenia, lymphopenia) linked to SLE and poorer outcomes. 1
• Comprehensive metabolic panel to evaluate renal function and exclude azotemia, which can falsely elevate inflammatory markers. 1
• Urinalysis with urine protein-to-creatinine ratio is critical for detecting lupus nephritis. 7, 1
• ESR (erythrocyte sedimentation rate) for baseline inflammatory assessment. 1

Critical Pitfall: Interpreting the Elevated RF

Do not diagnose rheumatoid arthritis based on isolated RF positivity without clinical arthritis. 5 In the context of a facial rash:

• RF can be positive in various autoimmune conditions, including lupus, but is not specific. 5
• The absence of joint symptoms, anti-CCP antibodies, and the presence of a facial rash make RA extremely unlikely.

If Biopsy Confirms Cutaneous Lupus

Use the Cutaneous Lupus Disease Area and Severity Index (CLASI) at each visit to quantify disease activity and damage. 1, 2

Exclude Systemic Lupus Erythematosus

Even with confirmed CLE, you must screen for systemic involvement:

• Neuropsychiatric symptoms: Screen for headache, cognitive impairment, mood disorders, seizures. 1
• Renal involvement: If urinalysis or creatinine is abnormal, obtain urine microscopy, renal ultrasound, and consider nephrology referral for kidney biopsy. 1
• Hematologic abnormalities: Cytopenias on CBC warrant further investigation. 1

Ongoing Monitoring

Regular monitoring every 6-12 months should include CBC, ESR, CRP, serum albumin, creatinine, urinalysis, anti-dsDNA, C3, and C4 levels. 1, 8

Alternative Diagnosis: Rosacea

If the biopsy does not show lupus-specific changes, consider rosacea, which can present with facial erythema in similar distributions and shows Th1/Th17-polarized inflammation with macrophage infiltration. 9 However, rosacea typically presents with telangiectasias, flushing, and papulopustular lesions, which should be clinically apparent.

What NOT to Do

• Do not rely solely on ANA testing for diagnosis, as it can be positive in other conditions. 1
• Do not skip histopathological confirmation even when clinical features are highly suggestive. 2
• Do not diagnose RA based on isolated RF without clinical arthritis and anti-CCP antibodies. 5