What is the differential diagnosis and treatment for Pityriasis (skin condition) alba versus Pityriasis versicolor in a young patient presenting with skin patches?

Pityriasis Alba vs Pityriasis Versicolor: Differential Diagnosis and Treatment

Key Distinguishing Features

Pityriasis alba is strongly associated with atopic diathesis and represents a milder form of atopic dermatitis, while pityriasis versicolor is a superficial fungal infection caused by Malassezia yeasts that requires antifungal treatment. 1

Clinical Presentation Differences

Pityriasis Alba:

• Hypopigmented patches with fine scale, typically on face, upper arms, and trunk 1
• Associated with atopic dermatitis history, dry skin, and eczematous conditions 1
• More common in children and adolescents with atopic diathesis 1
• No fungal organisms on microscopy 1

Pityriasis Versicolor:

• Hypopigmented, hyperpigmented, or erythematous scaly macules and patches predominantly on trunk, neck, and upper arms 2, 3
• Caused by Malassezia yeasts (lipophilic yeast) converting from blastospore to mycelial form 2, 4
• More common in young adults (peak age 21-30 years), males (69-71%), and those with oily skin, hyperhidrosis, or living in hot/humid climates 5, 3
• Hypopigmented lesions occur in 85.8% of cases 3
• KOH preparation shows characteristic "spaghetti and meatballs" appearance (hyphae and spores) in 69.9% of clinically suspected cases 3

Diagnostic Approach

For Pityriasis Alba:

• Clinical diagnosis based on appearance and association with atopic features 1
• Wood's light examination may accentuate hypopigmentation but shows no fluorescence 6
• KOH preparation is negative for fungal elements 1

For Pityriasis Versicolor:

• KOH preparation of skin scrapings is the primary diagnostic test, showing hyphae and yeast forms 3
• Wood's light examination may show yellow-gold fluorescence 7
• Culture is less useful (only 23% positive even when KOH positive) and not necessary for diagnosis 3
• Consider predisposing factors: outdoor occupation (57.5%), positive family history (33.6%), excessive sweating (31.8%), oily skin (21.1%), occlusive clothing (19.4%) 3

Treatment Recommendations

Pityriasis Alba Treatment

Topical emollients and mild-to-moderate potency corticosteroids are first-line, with treatment duration limited to avoid skin atrophy. 6

• Potent topical steroids for trial period of no more than 2 months due to risk of skin atrophy 6
• Topical calcineurin inhibitors (pimecrolimus or tacrolimus) as alternatives with better short-term safety profile 6
• Emollients to address underlying dry skin and atopic features 6
• Repigmentation occurs gradually over months; UV exposure may accelerate but is not primary treatment 7

Pityriasis Versicolor Treatment

Topical antifungals are first-line for localized disease, with oral ketoconazole reserved for extensive or recurrent cases, requiring at least 20 days of treatment. 8, 5

Topical Options:

• Ketoconazole 2% cream applied once daily for 2 weeks to affected and surrounding areas 8
• Ketoconazole shampoo, zinc pyrithione shampoo, selenium sulfide, or ciclopiroxamine for widespread involvement 2
• Propylene glycol as alternative topical agent 2

Systemic Treatment for Extensive Disease:

• Oral ketoconazole 200 mg daily for at least 20 days (10-day courses show higher relapse rates) 5
• Fluconazole or itraconazole for difficult cases, both effective and well-tolerated 2
• Males and those aged 21-30 years more commonly require systemic therapy due to extensive involvement 5, 3

Post-Treatment Considerations:

• Hypopigmentation persists for weeks to months after fungal eradication 7
• UV therapy may accelerate repigmentation by inducing melanosome maturation, though depigmented lesions are difficult to improve 7
• Prophylactic treatment is mandatory to prevent recurrence (60% report recurrent episodes) 2, 3
• Daily bathing with salicylic acid and sulfur soap recommended as preventive measure 5

Critical Pitfalls to Avoid

• Do not treat pityriasis alba with antifungals—it is not a fungal infection but rather an atopic/inflammatory condition 1
• Do not use potent topical steroids beyond 2 months for pityriasis alba due to risk of skin atrophy 6
• Do not use 10-day courses of oral ketoconazole for pityriasis versicolor—minimum 20 days required to prevent early relapse 5
• Do not expect immediate repigmentation in either condition; hypopigmentation persists for months after treatment 7
• Do not overlook recurrence prevention in pityriasis versicolor—prophylactic regimens are essential given 60% recurrence rate 2, 3