Dermatology MCQ - Inflammatory Dermatoses - Pityriasis alba

A 7-year-old boy with a history of mild atopic dermatitis presents with several ill-defined, hypopigmented, slightly scaly patches on his cheeks. The lesions are asymptomatic and became more noticeable after a family beach vacation, as they did not tan like the surrounding skin. What is the most likely diagnosis?

A. Tinea Versicolor
B. Vitiligo
C. Pityriasis Alba
D. Post-inflammatory Hypopigmentation
E. Morphea

Correct Answer: C. Pityriasis Alba

Explanation:

• The presentation is classic for Pityriasis Alba. Key diagnostic clues include the patient's age (child), personal history of atopy, location on the face (cheeks are most common), and the description of ill-defined, hypopigmented patches with fine scale. The history of the lesions becoming more prominent after sun exposure is highly characteristic, as the involved skin fails to tan. It is a benign, subclinical form of dermatitis.

• Why the other options are incorrect:

  • A. Tinea Versicolor: This fungal infection also causes hypopigmented, scaly patches. However, it is uncommon on the face alone in temperate climates and is more typically found on the neck, chest, and back. A KOH preparation would reveal short hyphae and spores ("spaghetti and meatballs" appearance), which would be negative in Pityriasis Alba.

  • B. Vitiligo: This condition presents with sharply demarcated, completely depigmented (milky white), not hypopigmented, macules. There is an absolute lack of pigment, scale is absent, and it is not associated with atopy or scaling.

  • D. Post-inflammatory Hypopigmentation: This is a possible consideration, as eczema can lead to this. However, Pityriasis Alba is a specific, primary clinical entity often categorized as a minor feature of atopic dermatitis. The term "Pityriasis Alba" is used for this classic facial presentation in children.

  • E. Morphea: This is a form of localized scleroderma. It presents with indurated, ivory-colored plaques, often with a lilac-colored border. The skin is hardened, which is not a feature of the soft, slightly scaly skin in Pityriasis Alba.

Key Points for Exams

• Epidemiology & Association: Extremely common in children, with a strong association with atopic dermatitis and dry skin (xerosis). It is more noticeable in individuals with darker skin phototypes.

• Pathophysiology: Thought to represent a post-inflammatory hypopigmentation following a subclinical, low-grade eczematous dermatitis.

• Clinical Course: The condition is benign and self-limiting. The hypopigmentation can persist for months to years but eventually resolves spontaneously. The scale is often transient and may not be present at the time of examination.

• Management:

  1. Emollients: The cornerstone of treatment to improve the underlying skin barrier and subclinical dryness/inflammation.

  2. Low-Potency Topical Corticosteroids: A short, intermittent course (e.g., hydrocortisone 1%) can be used to reduce any residual inflammation.

  3. Topical Calcineurin Inhibitors: Pimecrolimus cream or tacrolimus ointment are excellent alternatives, especially on the face, as they do not carry the risk of skin atrophy and are effective at reducing inflammation and repigmentation.

  4. Sun Protection: Crucial to minimize the contrast between lesional and sun-tanned skin and to protect the hypopigmented skin from sun damage.