Pityriasis Alba

Common benign eruption of ill defined, hypopigmented, finely scaly patches, mainly on the face of children and adolescents. It affects about 1 to 5% of children, with peak onset between 3 and 16 years.

• It is regarded as a mild, low grade eczematous process with post-inflammatory loss of pigment. The pigment loss reflects reduced melanocyte activity and reduced melanosome transfer, not melanocyte destruction.
• Strong association with atopy: dry skin, atopic dermatitis, asthma and allergic rhinitis in 30 to 50% of patients. Contributing factors are dry skin, frequent hot bathing, soap use, and sun exposure, which tans the surrounding normal skin and makes the pale patches more obvious. This is the main reason it is most noticed in summer and in dark skin.
• The condition is self-limiting. Each patch persists for months, and the whole process usually settles by early adulthood, though repigmentation can take 1 to 2 years.

• Round or oval, ill defined, hypopigmented (not depigmented) patches, 0.5 to 5 cm, with fine powdery scale. A pink, slightly raised edge may be seen in early lesions before the pale stage.
• Face (cheeks, perioral area, chin) in 50 to 90% of cases, followed by the upper arms, neck and shoulders, and less often the trunk and legs. Several patches are usual, and lesions are often asymmetrical.
• Extensive pityriasis alba affects the trunk and limbs in older children and adolescents, and is more resistant.
• Usually asymptomatic, with mild itch in a minority.
• Differential diagnosis: vitiligo (complete chalk white depigmentation, no scale), pityriasis versicolor (fine scale, yellow fluorescence), tinea corporis (active scaly edge), post-inflammatory hypopigmentation from other dermatoses, nevus depigmentosus (present from birth, stable), indeterminate or tuberculoid leprosy (reduced sensation, endemic areas), hypopigmented mycosis fungoides, hypopigmented macules of tuberous sclerosis (ash leaf, present from infancy), seborrhoeic dermatitis, and lichen sclerosus.
• Complications: cosmetic distress and recurrent episodes. There are no systemic effects and no scarring.

• Clinical, from the age, face distribution, scale, atopic background and the ill defined edge.
• Wood lamp shows hypopigmentation that is not accentuated to the chalk white of vitiligo.
• Potassium hydroxide preparation of scale if pityriasis versicolor or tinea is possible.
• Test light touch and pinprick sensation over patches in areas where leprosy occurs, and arrange slit skin smear and biopsy if sensation is reduced or a nerve is thickened.
• Biopsy only if the diagnosis is doubtful (it shows mild spongiosis, parakeratosis and reduced melanin).
• Examine for other features of atopy and tuberous sclerosis (three or more ash leaf macules in a child need further assessment).

• Reassure the family that the condition is harmless and resolves without scarring. Explain that treatment improves scale and speeds repigmentation but that colour return takes months.
• Skin care:
  • Use a soap free cleanser, lukewarm baths of short duration, and apply a bland emollient (white soft paraffin, or urea 5 to 10% cream) twice daily.
  • Apply broad spectrum sunscreen SPF 30 or more daily to the face and exposed skin, because tanning of the surrounding skin worsens the contrast and burned pale skin repigments poorly.
• Topical anti-inflammatory therapy for scaly or pink patches:
  • Hydrocortisone 1% cream twice daily for 1 to 2 weeks on the face. Avoid prolonged use because of thinning.
  • Mometasone furoate 0.1% cream once daily for 2 weeks on the body.
  • Tacrolimus 0.03% ointment (children aged 2 to 15 years) or 0.1% ointment (adults), or pimecrolimus 1% cream, applied twice daily for 4 to 12 weeks. These are preferred on the face for longer courses because they do not cause atrophy. Burning in the first days is common.
• Resistant extensive disease (specialist use, evidence limited): narrowband UVB phototherapy 2 to 3 times weekly for 3 to 6 months, or 308 nm excimer laser. Doses are set by skin type and minimal erythema dose.
• Calcipotriol 0.005% and topical antifungals have limited evidence, and antifungals are used only if Malassezia involvement is shown.
• Special groups:
  • Children: use the mildest effective steroid for short periods, emollients, and calcineurin inhibitors for the face.
  • Pregnancy: emollients, sunscreen and brief mild steroid. Avoid phototherapy with psoralens.
  • Dark skin: avoid irritant treatments that cause further pigment change.
• Follow up: review at 4 to 6 weeks, then every 3 to 6 months. Refer to dermatology if the diagnosis is uncertain, if patches are anaesthetic, if there is no improvement by 6 months, or for phototherapy.