School-Age Child with Hypopigmented Patches: Pityriasis Alba Versus Vitiligo Versus Tinea Versicolor
An 8-year-old girl presents with several ill-defined hypopigmented patches on the cheeks and upper arms that her mother noticed over the summer. The patches are mildly scaly and not itchy. She has a history of atopic dermatitis and uses emollients. She plays outdoor soccer and swims weekly. On exam, the patches are 1-3 cm, poorly demarcated, with fine scale; there is no complete depigmentation, and sensation is intact. A potassium hydroxide (KOH) prep from a scaly patch shows no fungal elements. Wood's lamp examination shows faint accentuation without sharp borders. The family is concerned about vitiligo because a cousin has it. The girl is self-conscious at school.
1. How do the clinical features and bedside tests favor pityriasis alba over vitiligo and tinea versicolor, and what is the role of the KOH and Wood's lamp findings?
Read the worked answer
The features favor pityriasis alba:
- Ill-defined, poorly demarcated patches with fine scale - typical of pityriasis alba; vitiligo is sharply demarcated and completely depigmented (chalk-white) without scale.
- History of atopic dermatitis - pityriasis alba is associated with atopy.
- Summer onset and outdoor activity - sun exposure unmasks the contrast between affected and tanned skin.
- No itch, intact sensation - argues against other neuropathic causes.
Bedside tests:
- KOH negative - argues against tinea versicolor (which would show short hyphae and spores) and against tinea corporis.
- Wood's lamp: vitiligo shows bright blue-white accentuation with sharp borders due to loss of melanin; pityriasis alba shows only faint accentuation without sharp borders, consistent with reduced (not absent) melanin. Tinea versicolor may show coppery or yellow-green fluorescence.
Conclusion: This is pityriasis alba, a self-limited post-inflammatory hypopigmentation seen with atopic dermatitis and sun exposure. Reassure the family, emphasize sun protection, and treat the underlying atopic dermatitis with emollients and topical anti-inflammatory therapy as needed.
2. The mother asks whether the patches will go away and whether bleaching creams or light therapy are needed. Provide counseling and a management plan.
Read the worked answer
Counseling:
- Pityriasis alba is self-limited and typically resolves over months to years, though it may recur with sun exposure. It does not progress to vitiligo.
- No bleaching creams - these are for hyperpigmentation and are inappropriate and potentially harmful here.
- Light therapy is not indicated for pityriasis alba.
Management plan:
- Sun protection: broad-spectrum sunscreen (SPF 30+) and protective clothing to reduce contrast between affected and tanned skin; this is the most visible intervention.
- Emollients daily and topical corticosteroid (low-potency, e.g., hydrocortisone 1% or desonide) to scaly or inflamed patches for short courses; avoid prolonged use on the face.
- Treat underlying atopic dermatitis to reduce recurrence.
- Reassurance and school support if self-conscious; the appearance improves with time.
- Follow-up in 2-3 months to confirm improvement and reassess if patches become sharply demarcated or completely depigmented (which would prompt evaluation for vitiligo).
Document the discussion, including that no fungal infection was found and that the condition is benign.