What is the diagnosis and treatment for erythematous raised patches of skin without scaling or blistering?

Diagnosis and Management of Erythematous Raised Patches Without Scaling or Blistering

Primary Diagnosis

The most likely diagnosis for erythematous raised patches without scaling or blistering is urticaria (hives) or early-stage bullous pemphigoid in its non-bullous phase, particularly in elderly patients with pruritus. 1, 2

Diagnostic Approach

Initial Clinical Assessment

Examine for specific morphologic features:

• Measure lesion size and document distribution pattern (symmetric vs. asymmetric, flexural surfaces vs. extensor surfaces) 1
• Assess lesion duration: Individual urticarial lesions resolve within 24 hours, while erythema multiforme lesions remain fixed for minimum 7 days 3
• Palpate for texture: Wooden-hard feel of subcutaneous tissue extending beyond visible erythema suggests necrotizing fasciitis requiring immediate surgical consultation 1, 4
• Check for target configuration: Atypical target lesions with purpuric centers suggest erythema multiforme 1, 3

Critical Historical Elements

Obtain medication history from the past 1-6 months, specifically asking about diuretics, psycholeptic drugs (phenothiazines), and checkpoint inhibitors, as these trigger bullous pemphigoid 1, 2

Document recent tick exposure or travel to Lyme-endemic areas, as erythema migrans presents as expanding erythematous patches in unusual locations like the axilla 4, 5

Ask about herpes simplex virus history or recent Mycoplasma pneumoniae infection, as these are the most common triggers for erythema multiforme 3, 6, 7

Differential Diagnosis Algorithm

If Patient is Elderly (>70 years) with Severe Pruritus:

Consider non-bullous bullous pemphigoid first, even without frank bullae 1, 2

• Obtain direct immunofluorescence (DIF) from perilesional skin—this is the single most critical diagnostic test showing linear IgG and/or C3 deposits along the dermoepidermal junction 1, 2
• Order serum ELISA for anti-BP180 and anti-BP230 antibodies 1, 2
• Skin biopsy may show only mild superficial perivascular lymphocytic infiltration with papillary edema in early disease 2

If Lesions are Expanding Over Days:

Consider erythema migrans (Lyme disease), especially if lesion increases in size over 1-2 days and occurs in unusual locations like axilla 4, 5

• Dermatoscopy shows collarette-shaped white scales around central punctum with red purpuric dots increasing toward periphery 5
• Do not wait for serology—start treatment immediately with doxycycline 100 mg twice daily for 10-21 days 4, 5

If Lesions Have Targetoid Appearance:

Consider erythema multiforme, which presents with fixed target lesions on extensor surfaces of extremities spreading centripetally 3, 6, 7

• Rule out Stevens-Johnson syndrome by absence of widespread purpuric macules with extensive blistering and mucosal involvement 1, 3
• Test for Mycoplasma pneumoniae and HSV as these are the most common triggers 3, 6, 7

If Patient Has Systemic Toxicity or Pain Disproportionate to Findings:

Immediately consider necrotizing fasciitis 1, 4

• Features include: edema extending beyond erythema, altered mental status, failure to respond to antibiotics, crepitus, bullous lesions, or skin necrosis 1
• Obtain immediate surgical consultation—do not delay for imaging 1

Treatment Algorithm

For Urticaria (Most Common):

• Topical hydrocortisone applied 3-4 times daily for symptomatic relief 8
• Second-generation H1-antihistamines for systemic control 3, 6

For Non-Bullous Bullous Pemphigoid:

• High-potency topical corticosteroids for localized disease 1
• Systemic corticosteroids (prednisone 0.5-1 mg/kg/day) for extensive involvement 1
• Discontinue any triggering medications identified in the 1-6 month window 1, 2

For Erythema Migrans:

• Doxycycline 100 mg twice daily for 10-21 days (first-line) 4, 5
• Alternative: amoxicillin or cefuroxime if doxycycline contraindicated 4

For Erythema Multiforme:

• Treat underlying infection (acyclovir for HSV, antibiotics for Mycoplasma pneumoniae) 3, 6, 7
• Topical corticosteroids or antihistamines for symptomatic relief 3, 6
• For recurrent HSV-associated disease: prophylactic antiviral therapy 3, 6, 7

For Erythrodermic Psoriasis (if generalized):

• Oral cyclosporine 3-5 mg/kg/day for rapid control in systemically ill patients 1
• Mid-potency topical corticosteroids with emollients under occlusion for comfort 1

Critical Pitfalls to Avoid

Do not dismiss raised erythematous patches in the axilla as simple irritant dermatitis—this location is highly unusual for bacterial cellulitis and should prompt consideration of erythema migrans 4

Do not rely on serology for early Lyme disease diagnosis—antibodies are often negative initially, and treatment should begin based on clinical presentation 4, 5

Do not delay surgical consultation if necrotizing fasciitis is suspected—clinical judgment trumps imaging, and delay can be fatal 1, 4

Do not rely on histopathology alone for bullous pemphigoid—always obtain DIF from perilesional skin in elderly patients with refractory pruritus, as histology may be nonspecific in non-bullous forms 1, 2

Do not confuse erythema multiforme with Stevens-Johnson syndrome—SJS has widespread purpuric macules with extensive blistering and prominent mucosal involvement, while EM has discrete targetoid lesions primarily on extremities 1, 3