What are the characteristic findings of Pityriasis (Pityriasis) Alba on physical exam?

Characteristic Findings of Pityriasis Alba on Physical Examination

Pityriasis alba presents as hypopigmented, slightly scaly patches with indistinct margins, most commonly occurring on the face of children, particularly those with darker skin tones or with a history of atopic dermatitis. 1

Key Physical Examination Findings

Primary Features

• Hypopigmented macules or patches: Variably hypopigmented areas that are more noticeable in darker skin types and after sun exposure 2, 3
• Fine scaling: Typically mild and may be more prominent in early stages 2
• Indistinct borders: Patches have poorly defined margins 2
• Distribution: Most commonly affects the face, particularly cheeks, but can also appear on the neck, upper arms, and shoulders 3
• Size: Usually 0.5-2 cm in diameter, but can vary 3
• Number: Multiple lesions are common, though solitary lesions occur in approximately 16% of cases 2

Secondary Characteristics

• Minimal to no inflammation: May have slight erythema in early stages 3
• Asymptomatic: Generally non-pruritic, though mild itching can occasionally occur 2
• No textural change: Unlike vitiligo, the skin texture remains normal except for the fine scaling 2
• Becomes more apparent with tanning: Sun exposure increases the contrast between normal and affected skin 3

Clinical Variants

• Common form: Facial lesions in children
• Extensive form: More generalized, symmetrical distribution with involvement of the trunk rather than the face; lesions tend to be less scaly but more persistent 4
• Pigmenting form: Rare variant with hyperpigmented borders 3

Histopathological Findings

Although not typically needed for diagnosis, histopathology shows:

• Markedly reduced pigment in the epidermis
• No significant difference in melanocyte count between lesional and normal skin
• Degenerative changes in melanocytes
• Reduced number of melanosomes within keratinocytes 2

Differential Diagnosis Features

When examining a patient with suspected pityriasis alba, it's important to distinguish it from:

• Vitiligo: Complete depigmentation with sharp borders
• Tinea versicolor: Fine scale with positive KOH examination
• Nevus depigmentosus: Present from birth, stable over time
• Nevus anemicus: Blanches with diascopy 3

Associated Findings

Pityriasis alba is recognized as an associated feature of atopic dermatitis, with approximately 18% of patients having a history of atopic dermatitis 2, 1. Other associated findings may include:

• Xerosis (dry skin)
• Keratosis pilaris
• Other atopic features 1, 3

Clinical Course

• Most lesions resolve spontaneously within 1 year, though some may persist longer
• Recurrence is common, especially with continued sun exposure without proper skin care
• Hypopigmentation may worsen temporarily after sun exposure before eventual resolution 3

Pityriasis alba is primarily a cosmetic concern rather than a medical one, with excellent prognosis for eventual resolution, though treatment may be sought to hasten repigmentation, particularly in patients with darker skin types where the contrast is more noticeable 5, 6.