What is the differential diagnosis of tinea?

Differential Diagnosis of Tinea

The differential diagnosis of tinea varies by anatomical location and clinical presentation, but broadly includes other dermatoses (eczema, psoriasis, seborrheic dermatitis, contact dermatitis, pityriasis rosea), other infectious etiologies (bacterial, viral, other fungal, parasitic), and inflammatory conditions—with laboratory confirmation essential to avoid misdiagnosis.

By Anatomical Site and Clinical Presentation

Tinea Capitis (Scalp)

The differential diagnosis depends on the clinical variant 1:

Non-inflammatory presentations may mimic:

• Seborrheic dermatitis - diffuse scaling without significant hair loss 1
• Psoriasis - well-demarcated plaques with silvery scale 1
• Alopecia areata - smooth patches of hair loss without scaling 2
• Atopic dermatitis - pruritic, poorly demarcated patches 1

Kerion (inflammatory, boggy mass) is commonly misdiagnosed as 1:

• Bacterial abscess - the most common misdiagnosis, though secondary bacterial infection can coexist 1
• Folliculitis - scattered pustules with low-grade inflammation 1
• Regional lymphadenopathy accompanies kerion and should not automatically suggest bacterial infection 1

Black dot pattern (broken hairs at scalp surface) may resemble:

• Trichotillomania - irregular patches from hair pulling 1
• Traction alopecia - hair loss along areas of tension 1

Favus variant (yellow crusted cup-shaped lesions) can be confused with:

• Impetigo - honey-colored crusts but lacks follicular involvement 1
• Severe seborrheic dermatitis - lacks the characteristic scutula formation 1

Tinea Corporis (Body)

Common mimics include 3, 4, 2:

• Eczema/atopic dermatitis - poorly defined borders, often bilateral and symmetric 2
• Psoriasis - thicker plaques with silvery scale, often on extensor surfaces 3
• Pityriasis rosea - herald patch followed by Christmas tree distribution 3
• Contact dermatitis - history of exposure, distribution matches contactant 3
• Granuloma annulare - lacks scale, firm papules in annular configuration 4
• Nummular eczema - coin-shaped lesions but typically more eczematous 3

Tinea Cruris (Groin)

Key differentials include 3, 4:

• Candidiasis - involves scrotum (tinea cruris typically spares), satellite lesions present 3
• Erythrasma - coral-red fluorescence under Wood's lamp, caused by Corynebacterium 3
• Inverse psoriasis - well-demarcated, lacks advancing scaly border 3
• Seborrheic dermatitis - more greasy scale, less defined borders 4
• Intertrigo - purely inflammatory, no fungal elements on KOH 3

Tinea Pedis (Feet)

Differential varies by presentation type 3, 2:

• Dyshidrotic eczema - vesicles on sides of feet/hands, intensely pruritic 3
• Contact dermatitis - from shoes or topical products 3
• Psoriasis - particularly palmoplantar type 3
• Juvenile plantar dermatosis - shiny, glazed appearance in children 3
• Pitted keratolysis - bacterial, characteristic odor and pitting 3

Onychomycosis (Nails)

Must distinguish from 2:

• Psoriatic nail dystrophy - oil drop sign, pitting, other psoriasis features 2
• Traumatic dystrophy - history of repeated low-level trauma, especially great toenails 2
• Lichen planus - pterygium formation, other mucocutaneous findings 2
• Bacterial paronychia - acute inflammation, purulence 2

Special Considerations in Immunocompromised Patients

In immunocompromised hosts, the differential diagnosis expands significantly 1:

Non-infectious mimics include:

• Drug eruptions - temporal relationship to medication initiation 1
• Cutaneous infiltration with underlying malignancy - particularly in hematologic malignancies 1
• Chemotherapy or radiation-induced reactions - distribution matches treatment field 1
• Sweet syndrome - tender erythematous plaques with neutrophilic infiltrate 1
• Erythema multiforme - target lesions, often mucosal involvement 1
• Leukocytoclastic vasculitis - palpable purpura, often lower extremities 1
• Graft-versus-host disease - in allogeneic transplant recipients 1

Infectious differentials are broader 1:

• Bacterial infections - including atypical organisms in neutropenic patients 1
• Other fungal infections - Candida, Aspergillus, endemic mycoses 1
• Viral infections - HSV, VZV, disseminated viral exanthems 1
• Parasitic infections - particularly in specific geographic exposures 1

Tinea Incognito

Tinea incognito represents an atypical presentation resulting from inappropriate topical corticosteroid use 5:

• Lacks the characteristic annular border and scale 5
• May present with increased erythema, pustules, or nodules 5
• Usually requires systemic antifungal treatment 5
• Should be suspected when "eczema" worsens or changes character with topical steroids 5

Critical Diagnostic Approach

Laboratory confirmation is essential because clinical diagnosis is unreliable 4, 2:

• KOH preparation showing hyphae/arthroconidia provides rapid confirmation 4, 2
• Fungal culture on Sabouraud agar is the gold standard for species identification 4
• Confirmation is mandatory for tinea capitis and onychomycosis before initiating systemic therapy 2
• Biopsy or aspiration should be performed early in immunocompromised patients with atypical presentations 1

Common Pitfalls

• Assuming all annular scaly lesions are tinea - many conditions produce ring-shaped lesions 3, 2
• Treating onychomycosis without confirmation - up to 50% of dystrophic nails are non-fungal 2
• Missing kerion and treating as bacterial abscess - delays appropriate antifungal therapy and risks scarring alopecia 1, 2
• Overlooking tinea incognito - prior steroid use masks typical features 5
• In immunocompromised patients, assuming localized lesions are benign - may represent disseminated life-threatening infection 1