Differential Diagnosis of Erythema by Topography

Introduction

Erythema appearing at specific anatomical sites often has a distinct, narrower differential diagnosis than generalized erythema. This chapter provides a systematic approach to erythema based on body region: Face, Palms/Soles, Diaper Area, Scrotal Region, and Intertriginous Areas (Intertrigo). Recognizing these topographical patterns allows for rapid diagnostic triage.

---

18.1 Facial Erythema

The face is a common site for erythema due to its rich vascularization, constant sun exposure, and sebaceous gland density. The distribution and associated features are key.

18.1.1 Paroxysmal Facial Erythema (Flushing)

18.1.2 Permanent Facial Erythema

A. Infectious Causes

• Erysipelas: Well-demarcated, raised, warm, tender plaque. Often unilateral. Fever/chills common.
• Herpes Zoster (V1): Dermatomal. May precede vesicles by 2-3 days. BEWARE: Hutchinson's sign (tip of nose) indicates risk of ocular involvement.
• Lupus Vulgaris (Cutaneous TB): Apple-jelly nodules on diascopy. Chronic, destructive.

B. Inflammatory/Autoimmune Causes

• Acute Cutaneous Lupus Erythematosus (ACLE):
  • Malar ("Butterfly") Rash: Bilateral, symmetric erythema on cheeks and bridge of nose. Characteristically SPARES the nasolabial folds.
  • Photosensitive: Worsens with sun exposure.
  • Associated Signs: Oral ulcers, arthritis, nephritis.
• Dermatomyositis:
  • Heliotrope Rash: Violaceous (dusky purple) erythema of the eyelids with periorbital edema.
  • Other Signs: Gottron's papules (over MCPs/PIPs), Shawl sign (upper back), V-sign (anterior chest).
• Seborrheic Dermatitis: Scaly, greasy erythema on eyebrows, glabella, nasolabial folds. Yellowish scale.
• Rosacea: Centrofacial telangiectatic erythema, papulopustules. Spares periocular areas.
• Perioral Dermatitis: Erythematous papules and pustules around the mouth. Often steroid-induced.

C. Neoplastic Causes

• Angiosarcoma: Indurated, violaceous, bruise-like plaque or nodule on the scalp or face of elderly patients. HIGH MORTALITY.
• Mycosis Fungoides (Facies Leonina): Infiltrated erythema and plaques.
• Acrokeratosis Paraneoplastica (Bazex): Violaceous, keratotic erythema on nose and ears. Associated with aerodigestive tract cancers.

---

18.2 Palmar and Plantar Erythema (Acral Erythema)

Erythema on palms and soles has specific etiologies differing from other body sites.

18.2.1 Palmar Erythema (General)

18.2.2 Specific Palmoplantar Erythematous Conditions

• Chemotherapy-Induced Acral Erythema (Hand-Foot Syndrome):
  • Causative Agents: Capecitabine, Doxorubicin, Cytarabine, 5-FU.
  • Presentation: Symmetric, painful erythema of palms and soles, progressing to edema, blistering, and desquamation.
  • Timing: 2-12 days after chemotherapy cycle.
• Erythermalgia (Erythromelalgia):
  • Features: Paroxysmal burning pain, warmth, and redness of extremities (palms, soles, ears).
  • Triggers: Heat, dependency.
  • Relief: Immersion in cold water.
  • Associations: Myeloproliferative neoplasms (Polycythemia Vera, Essential Thrombocythemia), small fiber neuropathy, idiopathic.
• Kawasaki Disease (Children):
  • Mucocutaneous Lymph Node Syndrome: Fever >5 days + conjunctivitis + rash + lymphadenopathy + strawberry tongue + palmoplantar erythema with edema, followed by desquamation.
  • CRITICAL: Risk of coronary artery aneurysms. Requires IVIG treatment.
• Palmoplantar Pustulosis: Sterile pustules on an erythematous base. Strong association with smoking and psoriasis.
• Lupus Erythematosus: Chilblain lupus can affect acral areas.

---

18.3 Diaper Erythema (Diaper Dermatitis)

Erythema in the diaper area of infants requires careful assessment of distribution and morphology.

18.3.1 Irritant Contact Dermatitis (Most Common)

• Distribution: Convexities (buttocks, inner thighs, lower abdomen). SPARES the folds (W-sign).
• Features: Shiny, glazed erythema. Erosions may occur with severe friction.
• Cause: Prolonged contact with urine (ammonia) and feces.

18.3.2 Candida Diaper Dermatitis

• Distribution: Involves the folds (crural creases). Beefy red erythema.
• Hallmark: Satellite papules and pustules beyond the main erythematous area.
• Confirmation: KOH preparation shows pseudohyphae.

18.3.3 Seborrheic Dermatitis

• Distribution: Folds involved. May extend to scalp (Cradle Cap) and retroauricular areas.
• Features: Greasy, yellowish scale on an erythematous base. Well-demarcated.

18.3.4 Psoriasis (Napkin Psoriasis)

• Distribution: Well-demarcated, shiny red plaques. May affect folds.
• Features: Lack of typical silvery scale (due to maceration). Often the first manifestation of psoriasis in infants.

18.3.5 "Do Not Miss" Diagnoses in Diaper Rash

[!CAUTION] Red Flags

• Langerhans Cell Histiocytosis (LCH):
  • Features: Petechiae, purpura, erosive papules, and crusting within the erythematous areas. Resistant to standard diaper rash treatment.
  • Distribution: Often involves folds and can spread beyond diaper area.
  • Action: Biopsy. Systemic workup.
• Zinc Deficiency (Acrodermatitis Enteropathica):
  • Features: Periorificial (mouth, anus) and acral erosive dermatitis. Diarrhea, alopecia.
  • Cause: Inherited (AR) or acquired (malnutrition, TPN without zinc).
• Congenital Syphilis:
  • Features: Bullae and erosions on palms/soles ("Snuffles" = rhinitis). Hepatosplenomegaly.

---

18.4 Scrotal Erythema

Scrotal skin is thin and highly vascular, making it susceptible to specific conditions.

---

18.5 Intertrigo (Erythema of Skin Folds)

Intertrigo refers to inflammation of apposing skin surfaces in body folds (submammary, abdominal pannus, axillae, groin, interdigital).

18.5.1 Common Causes

• Irritant Dermatitis (Maceration): Friction, moisture, heat. Erythema, fissuring, erosions.
• Candidiasis: Beefy red erythema with satellite pustules. Most common infectious cause.
• Erythrasma: Well-demarcated, brownish-red patches. Caused by Corynebacterium minutissimum. Coral-red Wood's lamp fluorescence.
• Tinea Cruris / Tinea Corporis: Annular plaques with raised, scaly borders. Active edge.
• Inverse Psoriasis: Shiny, well-demarcated red plaques. Lack of scale due to moisture.
• Seborrheic Dermatitis: Greasy scale on erythematous base.

18.5.2 "Do Not Miss" Causes of Intertrigo

[!WARNING] Red Flags

• Langerhans Cell Histiocytosis: Erosive, crusted papules in folds, especially in infants. Resistant to treatment.
• Hailey-Hailey Disease (Familial Benign Pemphigus): Recurrent erosive, crusted plaques in flexures. Genetic (AD, ATP2C1).
• Pemphigus Vegetans: Vegetating, hypertrophic plaques in folds. Acantholysis on biopsy.
• Necrolytic Migratory Erythema (Glucagonoma): Migratory, annular, erosive erythema with collarette scaling. Associated with pancreatic glucagonoma.
• Primary HIV Infection: Acute retroviral syndrome can present with flexural rash.
• Drug Eruption (AGEP/DRESS with intertrigo): Multiple fold involvement can be a sign of severe drug reaction.

---

18.6 Diagnostic Flowchart: Topographic Erythema

Loading diagram...

---

18.7 Summary Table: Erythema by Topography