Figurate Erythemas
Figurate (annular) erythemas are a group of reactive dermatoses with a distinctive shape: red lesions that form rings (annular), arcs (arcuate), overlapping circles (polycyclic), or wood-grain bands. Their defining biological feature is centrifugal spread: the lesion expands outward while the center gradually fades and returns to normal.
Figurate erythemas are not a single standalone disease. They are a pattern of cutaneous hypersensitivity reaction to a wide range of internal and external triggers: infections (fungal, bacterial, viral), drug allergies, autoimmune disease, or a warning sign of a paraneoplastic process. At Haute-Derma, evaluating a patient with a figurate erythema means combining close morphologic examination, histopathology, and a systematic whole-body workup to track down the underlying cause.
Pathogenesis and Immune Mechanisms of Figurate Erythemas
The characteristic formation and spread of figurate erythemas stem from a complex chain of immune reactions around the superficial and deep dermal blood vessels:
- Delayed (type IV) hypersensitivity: When the body encounters an external antigen (bacterial toxins, fungal components, drugs) or an internal one (tumor antigens, autoimmune complexes), antigen-presenting cells (dendritic/Langerhans cells) recruit and activate specific CD4+ and CD8+ T-cell clones.
- Centrifugal propagation: Activated T cells migrate outward along the dermal microvascular network. Inflammatory cytokines (TNF-alpha, IFN-gamma, IL-2) released at the advancing edge cause vasodilation, leaky vessel walls, and white-cell migration, producing a raised red ridge at the periphery. In the center, meanwhile, inflammation is switched off by regulatory T cells (Tregs) or by local depletion of antigen, giving the typical "central clearing."
- Classification by depth:
- Superficial patterns: Inflammation clusters around vessels of the superficial dermal plexus, often causing epidermal edema and spongiosis and producing scale on the inner edge of the ring (trailing scale).
- Deep patterns: A dense infiltrate wraps around deep dermal vessels (the "coat-sleeve" infiltrate) without epidermal edema, so the lesions feel firm and raised but the surface is completely smooth, with no scale.
Differential Diagnosis and Workup for Underlying Causes at Haute-Derma
Because figurate erythemas are easily mistaken for common skin conditions, Haute-Derma follows a standard three-step diagnostic process:
- Ruling Out Tinea Corporis
- Body ringworm also forms expanding rings, but its scale sits on the outer, advancing edge (leading scale), often with tiny pustules.
- A KOH 10–20% preparation of skin scrapings, looking for septate hyphae, is mandatory before any other figurate erythema is diagnosed.
- Skin Biopsy
- A 4 mm punch biopsy is taken across the advancing edge so that it includes both the cleared center and the red ridge.
- Hematoxylin and eosin (H&E) staining:
- Superficial EAC: Mild epidermal spongiosis with a T-cell infiltrate around superficial vessels.
- Deep EAC: Deep dermal vessels encased in a dense cuff of T cells (coat-sleeve pattern).
- Granuloma annulare: Areas of degenerated dermal collagen (necrobiosis) surrounded by macrophages/epithelioid cells and multinucleated giant cells (a granulomatous reaction).
- Screening for Systemic and Paraneoplastic Disease
- Blood tests: complete blood count (CBC), inflammatory markers (ESR/CRP), ASO titer (for streptococcal infection), liver and kidney function, fasting glucose, HbA1c, and lipids.
- Autoimmune panel: ANA, anti-dsDNA, anti-Ro/SSA, and anti-La/SSB (to rule out subacute cutaneous lupus erythematosus, SCLE).
- Paraneoplastic screening (especially with erythema gyratum repens or long-lasting, treatment-resistant EAC): chest and abdominal X-ray/CT, breast/pancreatic ultrasound, upper endoscopy and colonoscopy, and tumor markers (CEA, CA 125, CA 19-9, PSA).
Treatment and Control of the Underlying Cause
The guiding principle in treating figurate erythemas is that treating the underlying cause is the key, and topical treatment only plays a supporting role:
- Eliminating the Underlying Cause
- Infection or fungus: a full course of targeted therapy (doxycycline for Lyme disease; amoxicillin/penicillin for rheumatic fever; antifungals for skin or intestinal fungal infection).
- Drug allergy: stop all suspected drugs immediately (NSAIDs, antibiotics, diuretics).
- Paraneoplastic (EGR): surgical removal of the primary tumor or chemotherapy/radiotherapy. The wood-grain rash usually disappears completely once the tumor is successfully treated.
- Topical Symptom Control
- Topical corticosteroids: Medium- to high-potency agents (betamethasone dipropionate, clobetasol propionate) applied to the advancing edge to reduce inflammation and itch.
- Topical calcineurin inhibitors (tacrolimus 0.1% / pimecrolimus 1%): A safe alternative for thin skin (face, neck, skin folds) that avoids steroid-induced skin thinning.
- Systemic Therapy and Phototherapy for Chronic Cases
- Second-generation antihistamines: Needed to control intense itching (especially in EGR).
- Immunomodulators: Dapsone (50–100 mg/day) or hydroxychloroquine (200–400 mg/day) works well for treatment-resistant deep EAC or disseminated granuloma annulare (GA).
- Phototherapy: Narrowband UVB (311 nm) or PUVA effectively suppresses the T-cell response in the skin for widespread lesions.
