What could be the cause and treatment of small circular skin lesions?

Differential Diagnosis and Management of Small Circular Skin Lesions

Small circular skin lesions on the skin require systematic evaluation based on morphology, with the most common causes being tinea corporis (fungal infection), erythema multiforme, granuloma annulare, and nummular eczema—each requiring distinct diagnostic approaches and treatments.

Initial Diagnostic Approach

The morphology of the circular lesions is critical for narrowing the differential diagnosis:

Target or "Iris" Lesions with Concentric Rings

• Erythema multiforme presents with characteristic target lesions consisting of a dark red center surrounded by a pink ring with well-defined circular appearance 1
• These lesions have dusky red and white concentric rings in a targetoid morphology 1
• Lesions remain fixed for a minimum of 7 days, distinguishing them from urticaria which resolves within 24 hours 1
• Most commonly triggered by HSV infection, appearing approximately 10 days after viral infection due to cytotoxic T lymphocyte-mediated keratinocyte apoptosis 1
• Treatment is primarily supportive with topical corticosteroids for symptomatic relief 2

Annular Scaly Lesions with Central Clearing

• Tinea corporis typically presents as pruritic, annular, erythematous patches that grow centrifugally 3
• Diagnosis confirmed by potassium hydroxide (KOH) examination of skin scrapings showing fungal elements 4, 3
• Treatment with topical antifungals (for localized lesions) or systemic antifungals (for extensive disease) is usually curative 4

Non-Scaly Annular Plaques with Indurated Borders

• Granuloma annulare presents as nonscaly, annular plaques with indurated borders, typically on extremities 4, 3
• Approximately 50% of cases resolve spontaneously within two years 4
• Observation is often appropriate given the self-limited nature; intralesional corticosteroids may be considered for symptomatic or cosmetically concerning lesions 4

Coin-Shaped Papulovesicular Lesions

• Nummular eczema appears as coin-shaped papulovesicular erythematous lesions 3
• Treatment focuses on reducing skin dryness with liberal emollient use and topical corticosteroids 3, 5
• Apply topical hydrocortisone to affected areas 3-4 times daily 2

Critical Red Flags Requiring Urgent Evaluation

Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN)

If lesions progress to show any of the following features, immediate hospital admission is mandatory:

• Flat atypical targets or purpuric macules with epidermal detachment 1, 6
• Positive Nikolsky sign (epidermis peels with minimal shearing force) 6
• Extensive skin tenderness with flaccid bullae 6
• Patients with >10% body surface area involvement require immediate transfer to burn center or ICU 6
• Document all medications taken in the 2 months prior to symptom onset, as drugs (allopurinol, carbamazepine, lamotrigine, sulfonamides) are common triggers 6

Additional Differential Considerations

Pityriasis Rosea

• Multiple small, fawn-colored lesions with raised, scaly borders distributed along skin cleavage lines 4, 3
• Generally self-limited; treatment is symptomatic 4

Urticaria

• Well-circumscribed, erythematous lesions with raised borders and blanched centers 3
• Lesions are evanescent and lack scale 4
• Individual lesions resolve within 24 hours, unlike fixed annular dermatoses 1

Less Common but Important Diagnoses

• Subacute cutaneous lupus erythematosus: annular form on sun-exposed surfaces 4, 3
• Secondary syphilis: consider in appropriate clinical context 3
• Lyme disease (erythema migrans): expanding annular erythematous patch; requires prompt antibiotic therapy 3

Practical Management Algorithm

1. Document lesion characteristics precisely: photograph lesions, mark borders to track progression, measure size 1, 7
2. Perform KOH examination if scaly annular lesions suggest tinea corporis 4, 3
3. Apply topical corticosteroids (hydrocortisone 2% 3-4 times daily) for symptomatic relief in inflammatory conditions 2
4. Keep affected areas clean and dry between applications 7
5. Instruct patients to seek immediate attention if lesions become increasingly painful, develop blistering, or are associated with fever 7
6. Consider biopsy for atypical presentations, non-healing lesions, or when diagnosis remains uncertain after initial evaluation 8

Common Pitfalls to Avoid

• Do not assume all circular lesions are fungal infections—failure to recognize erythema multiforme or early SJS/TEN can have serious consequences 1, 6
• Do not use topical corticosteroids on suspected fungal infections without confirming diagnosis, as this can worsen tinea corporis 4
• Do not dismiss fixed lesions as urticaria—true urticarial lesions are transient (<24 hours) 1
• Do not delay specialist referral for rapidly progressive lesions, extensive involvement, or diagnostic uncertainty 7, 6