What is Pityriasis Alba
Pityriasis alba is a common benign hypopigmentation disorder primarily affecting children and adolescents, characterized by ill-defined, hypopigmented patches with fine scaling, most commonly on the face and upper body, strongly associated with atopic dermatitis. 1, 2
Clinical Presentation
Pityriasis alba presents with distinctive features that evolve through stages:
- Hypopigmented patches measuring up to several centimeters in diameter, typically appearing on the face, upper arms, trunk, and neck 2, 3
- Fine scaling that becomes apparent on scraping the lesions 4
- Indistinct borders with white structureless spots visible on dermoscopic examination 4
- Normally pigmented hairs within the affected patches, which helps distinguish it from other hypopigmentation disorders 4
- Lesions may be preceded by erythematous changes before hypopigmentation develops 2
- Mild pruritus may accompany the patches 2
The condition is markedly more visible in darker skin phototypes, though it can occur in all skin types, making it particularly concerning for patients and families with skin of color 2, 3
Etiology and Pathogenesis
The exact cause remains unknown, but several factors are implicated:
- Strong association with atopic diathesis, with pityriasis alba considered a milder form of atopic dermatitis 1, 2
- Poor cutaneous hydration and xerosis appear to be common underlying mechanisms 3
- Sun exposure exacerbates the contrast between normal and lesional skin, making lesions more visible 3
- Potential triggering factors include beauty treatments and microorganisms 2
- The end result is inappropriate melanosis manifesting as hypopigmentation 3
Histologically, lesions show consistent spongiosis, follicular spongiosis, focal parakeratosis, and acanthosis with superficial perivascular lymphocytic infiltrate 5
Differential Diagnosis
Critical distinctions must be made from other hypopigmentation disorders, particularly in darker-skinned populations where these conditions carry significant social implications:
- Pityriasis versicolor: Shows fine scale on scraping and positive KOH preparation, unlike pityriasis alba 6
- Vitiligo: Presents as depigmented (not hypopigmented) patches without scaling, often symmetrical, with complete loss of pigmentation 7, 3
- Nevus depigmentosus and nevus anemicus: Congenital lesions that do not change over time 3
- Leprosy: Must be excluded in endemic areas due to serious implications 4
Wood's light examination can be used to accentuate hypopigmentation, though pityriasis alba shows no fluorescence 1
Management Approach
First-line treatment consists of topical emollients combined with mild-to-moderate potency corticosteroids, with treatment duration carefully limited to avoid skin atrophy. 1
Treatment Algorithm:
Initial therapy:
- Emollients to address underlying dry skin and atopic features 1, 3
- Mild-to-moderate potency topical corticosteroids for inflammatory component 1
- Patient education on proper skin care and hygiene 3
For persistent cases:
- Potent topical steroids may be used for a trial period of no more than 2 months due to atrophy risk 1
- Topical calcineurin inhibitors (tacrolimus or pimecrolimus) serve as alternatives with a better short-term safety profile and play a crucial role in pharmacotherapy 1, 2, 3
Important Caveats:
- The condition follows an extended, multistage course with spontaneous remissions and recurrences 2
- Sun protection counseling is essential, as UV exposure increases the visibility of lesions 3
- Reassurance is critical, as the condition is benign and self-limited 2
- Dermoscopy can serve as a valuable diagnostic tool, showing four consistent criteria: white structureless spots, scaling, indistinct borders, and normally pigmented hairs 4