Clinical Differences Between Pityriasis Alba and Pityriasis Versicolor in Children
Pityriasis alba presents as ill-defined, scaly hypopigmented patches primarily on the face (especially cheeks) in atopic children, while pityriasis versicolor shows well-demarcated hypopigmented or hyperpigmented macules with fine scale predominantly on the trunk, confirmed by positive KOH examination showing fungal elements. 1
Key Distinguishing Features
Location and Distribution
- Pityriasis alba most commonly affects the face, particularly the cheeks and forehead, though it can occur on the upper body 2, 1
- Pityriasis versicolor preferentially involves seborrheic areas, especially the upper trunk in adolescents, though facial involvement (particularly the forehead) occurs in 47.5% of pediatric cases 1, 3
Lesion Characteristics
- Pityriasis alba presents as ill-defined, poorly demarcated patches with incomplete pigment loss and fine scale 1
- Pityriasis versicolor shows well-demarcated macules that can be hypopigmented, hypochromic, or hyperpigmented with characteristic fine, pityriasiform scale 4, 3
Pigment Loss Pattern
- Pityriasis alba demonstrates incomplete hypopigmentation (not complete depigmentation) due to inappropriate melanosis rather than melanocyte destruction 2
- Pityriasis versicolor alba can show both hypopigmentation and true depigmentation, with the achromic/hypochromic variant predominating in children (72% of cases) 3
Diagnostic Confirmation
Clinical Examination
- Pityriasis alba diagnosis is clinical, with no specific diagnostic test required 2, 1
- Pityriasis versicolor requires mycological confirmation: KOH examination reveals characteristic hyphae and yeast forms of Malassezia species 1, 4
Adhesive Tape Test
- Pityriasis versicolor can be confirmed using adhesive tape patch testing, which provides high diagnostic specificity (negative in all controls with eczema or vitiligo) 3
- Pityriasis alba does not require or benefit from adhesive tape testing 2
Associated Conditions and Risk Factors
Pityriasis Alba
- Strongly associated with atopic diathesis and considered a milder form of atopic dermatitis 5, 1, 6
- Risk factors include xerosis, poor cutaneous hydration, and potentially mineral deficiencies 2
- More visible in darker skin types due to contrast, though occurs in all phototypes 2
Pityriasis Versicolor
- Caused by Malassezia yeast species (fungal infection) 4
- More common in warm, humid climates 3
- Not associated with atopy 4
Age Distribution
- Pityriasis alba primarily affects children and adolescents, with typical onset in childhood 6
- Pityriasis versicolor in children ranges from 5 months to 14 years (mean 11 years), though it is less common in younger children compared to adolescents 3
Clinical Course
- Pityriasis alba follows an extended, multistage course with spontaneous remissions and recurrences, often preceded by erythematous changes 6
- Pityriasis versicolor shows persistent hypopigmentation after treatment of the active infection, which can be difficult to improve even with UV therapy 4
Common Pitfall to Avoid
The most critical error is failing to perform KOH examination or adhesive tape testing when pityriasis versicolor is suspected, as this is the definitive way to distinguish it from pityriasis alba and other hypopigmentation disorders 1, 3. The presence of fungal elements on microscopy immediately confirms pityriasis versicolor and directs appropriate antifungal treatment rather than the emollient-based approach used for pityriasis alba 2, 4.