What is the differential diagnosis and recommended diagnostic tests for an 11-year-old female with itching, erythema, central clearing, annular lesions, hyperpigmentation, and morning facial swelling?

Differential Diagnosis and Diagnostic Workup

Primary Differential Diagnosis

This clinical presentation of annular lesions with central clearing, itching, hyperpigmentation, and morning facial swelling in an 11-year-old female most strongly suggests tinea corporis (ringworm) with possible secondary allergic or atopic dermatitis, though systemic lupus erythematosus with nephrotic syndrome must be urgently excluded given the facial swelling.

Key Differential Diagnoses to Consider

Most Likely Diagnoses

• Tinea corporis (widespread): Annular papulosquamous lesions with central clearing are pathognomonic for dermatophyte infection 1
• Atopic dermatitis with secondary infection: The 6-month duration, pruritus, and hyperpigmentation fit this pattern, though the annular morphology is atypical 1, 2
• Urticaria pigmentosa (cutaneous mastocytosis): Can present with hyperpigmented lesions and pruritus in children, though typically appears before age 2 1, 2

Critical to Exclude (Due to Facial Swelling)

• Systemic lupus erythematosus (SLE): Morning facial swelling suggests possible nephrotic syndrome or renal involvement; annular lesions can occur in subacute cutaneous lupus
• Nephrotic syndrome (any cause): Morning facial edema is a hallmark finding
• Dermatomyositis: Can present with facial edema, though typically has heliotrope rash

Other Considerations

• Granuloma annulare: Presents with annular lesions but typically non-pruritic 1
• Erythema annulare centrifugum: Annular erythema with central clearing but less commonly pruritic
• Pityriasis rosea: Can have annular lesions but typically self-limited over weeks, not months

Essential Diagnostic Tests

Immediate Priority Tests (Due to Facial Swelling)

Complete metabolic panel with renal function: Urgently assess for proteinuria, hypoalbuminemia, and elevated creatinine to evaluate for nephrotic syndrome or lupus nephritis 1

Urinalysis with microscopy: Check for proteinuria, hematuria, and cellular casts 1

Complete blood count with differential: Assess for anemia, thrombocytopenia, or eosinophilia 1, 3

Antinuclear antibody (ANA) and anti-double stranded DNA: Screen for systemic lupus erythematosus 3

Complement levels (C3, C4): Low levels suggest active lupus with renal involvement 3

Serum albumin and total protein: Evaluate for hypoalbuminemia causing edema 1

Dermatologic Diagnostic Tests

Skin scraping with KOH preparation and fungal culture: This is the definitive test for tinea corporis and should be performed from the active border of annular lesions 1

Darier's sign assessment: Rub the hyperpigmented lesions to check for urtication (wheal formation), which is positive in 89-94% of mastocytosis cases 1, 2

Serum tryptase level: Elevated in mastocytosis (>20 μg/L indicates increased mast cell burden) 1, 2

Skin biopsy with immunofluorescence: If fungal studies are negative and autoimmune disease is suspected, obtain from lesional skin with perilesional tissue for direct immunofluorescence 1

• Request hematoxylin & eosin staining, Giemsa staining, and immunostaining for tryptase and KIT if mastocytosis suspected 1
• Request immunofluorescence for IgG, IgA, IgM, and C3 deposition if lupus or other autoimmune bullous disease suspected 1

Additional Recommended Tests

Serum IgE level: May be elevated in atopic dermatitis or inversely related to eosinophil counts in certain conditions 1, 3

Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP): Assess for systemic inflammation 3

Thyroid function tests: Recommended for evaluation of hyperpigmentation in axilla and neck regions 4

Wood's lamp examination: Can help differentiate epidermal from dermal pigmentation and identify erythrasma (coral-red fluorescence) 4

Clinical Examination Priorities

Assess Darier's sign: Firmly stroke the hyperpigmented lesions with a tongue depressor; positive urtication within 2-5 minutes suggests mastocytosis 1, 2

Evaluate distribution pattern: Flexural involvement suggests atopic dermatitis, while trunk and extremities favor mastocytosis or tinea 1, 2

Examine for scale at lesion borders: Active scaling at the periphery of annular lesions strongly suggests tinea corporis 1

Document facial swelling characteristics: Note if periorbital (suggests nephrotic syndrome), malar distribution (suggests lupus), or generalized 1

Check for lymphadenopathy: Cervical or generalized lymphadenopathy may suggest systemic disease 1

Assess for systemic symptoms: Document fever, night sweats, weight loss, or flushing which may indicate mastocytosis or systemic disease 1, 2

Critical Pitfalls to Avoid

Do not dismiss morning facial swelling as allergic edema without excluding renal disease: This is a red flag for nephrotic syndrome or lupus nephritis requiring urgent evaluation 1

Do not assume atopic dermatitis without confirming negative fungal studies: Annular lesions with central clearing are more characteristic of tinea corporis 1

Do not overlook mastocytosis in a child with chronic pruritic hyperpigmented lesions: Always perform Darier's sign and consider serum tryptase 1, 2

Avoid skin biopsy before fungal studies: KOH preparation and culture are non-invasive and should be performed first 1

Do not ignore the 6-month duration: This chronicity argues against simple allergic reactions and demands thorough investigation 2