✅ Model Answer: • Condition: Tinea versicolor (pityriasis versicolor).
• Appearance: Hypopigmented or hyperpigmented macules with fine, adherent scaling. Lesions are well-demarcated, often confluent, and commonly located on the neck, chest, back, and proximal upper extremities. The scale is easily scraped off. Lesions do not tan, so they become more noticeable after sun exposure.

✅ Model Answer: • Etiologic agent: Malassezia furfur (also known as Malassezia globosa), a lipophilic yeast.
• Characteristics: It is part of the normal skin flora in sebaceous areas. Under conditions of warmth, humidity, and increased sebum production, the yeast shifts from a yeast form to a hyphal form (mycelial phase), causing the clinical manifestations.

✅ Model Answer: • Pathophysiology: Malassezia furfur produces azelaic acid, a dicarboxylic acid, as a byproduct of lipid metabolism.
• Azelaic acid inhibits tyrosinase, the enzyme responsible for melanin synthesis, leading to hypopigmentation.
• In some cases, the yeast can also cause a mild inflammatory response, leading to hyperpigmentation.
• The scale in the lesions is due to the accumulation of yeast cells and keratinocytes (hyphae + spores).

✅ Model Answer: • Risk factors:
- Adolescence and young adulthood (increased sebum production).
- Warm, humid climates (tropical/subtropical regions).
- Excessive sweating (hyperhidrosis).
- Oily skin (seborrheic dermatitis).
- Immunosuppression (malnutrition, HIV, corticosteroid use).
- Genetic predisposition (familial cases).
- Poor hygiene.

✅ Model Answer: • KOH prep finding: "Spaghetti and meatballs" appearance.
- Spaghetti: Short, curved hyphae (mycelial fragments).
- Meatballs: Clusters of budding yeast spores (blastospores).
• The KOH preparation of skin scrapings from the scaly lesions shows both hyphae and spores, confirming the diagnosis of tinea versicolor.

✅ Model Answer: • Wood lamp (Wood's light): Ultraviolet light (365 nm) used in dermatology.
• Findings: Lesions of tinea versicolor may show yellow-gold (yellow-green) fluorescence under Wood lamp.
• Significance: Helps differentiate tinea versicolor from other hypopigmented conditions (e.g., vitiligo, which does not fluoresce).
• Limitation: Not all lesions fluoresce (especially if scale is scant or if the patient has washed recently). It is a helpful adjunct but not diagnostic.

✅ Model Answer: • Differential diagnoses:
- Vitiligo: Complete depigmentation (milk-white), no scaling, no fluorescence, progressive.
- Pityriasis alba: Dry, hypopigmented patches with fine scale, typically on the face in children; caused by mild eczema.
- Tinea corporis (ringworm): Annular lesion with central clearing and active border; scaling is more prominent; KOH shows hyphae only (not spores).
- Seborrheic dermatitis: Greasy, yellowish scales on the scalp, face, and chest; not hypopigmented.
- Post-inflammatory hypopigmentation: History of prior inflammation (eczema, psoriasis); no scale.
- Leprosy (hypopigmented lesions): Associated with sensory loss, thickened nerves, endemic areas.

✅ Model Answer: • Management:
- Topical treatments (first-line):
- Selenium sulfide 2% shampoo: Apply to affected areas, leave for 10 minutes, then rinse. Repeat daily for 1-2 weeks (or 1x/week for maintenance).
- Ketoconazole 2% shampoo: Apply to affected areas, leave for 5 minutes, then rinse. Repeat daily for 3 days (or as a single application).
- Other topical antifungals: Clotrimazole, miconazole, terbinafine (cream/gel).
- Oral treatments (extensive or recurrent):
- Fluconazole: 300-400 mg single dose OR 150 mg weekly for 2-4 weeks.
- Itraconazole: 200 mg daily for 5-7 days OR 200 mg BID for 1 day.
- Ketoconazole: 400 mg single dose (less commonly used due to liver toxicity).
- Maintenance: Once-weekly topical application to prevent recurrence.

✅ Model Answer: • Sun exposure effect:
- The yeast produces azelaic acid, which inhibits tyrosinase → reduces melanin production in the affected areas.
- When the surrounding skin tans after sun exposure, the hypopigmented lesions become more noticeable because they do not tan.
- This is a key clinical feature and helps differentiate tinea versicolor from other hypopigmented conditions.
- The lesions may also become more pronounced during summer months.

✅ Model Answer: • Prognosis: Excellent with treatment; lesions respond well to topical or oral antifungals.
• Recurrence: Very high (up to 80% within 1 year) because the yeast is a normal skin commensal and cannot be permanently eradicated.
• Prevention: Maintenance therapy (once-weekly topical application of selenium sulfide or ketoconazole shampoo) can reduce recurrence.
• Repigmentation: Hypopigmentation may take weeks to months to resolve after treatment (requires melanocyte recovery).
• Patient education: Advise patients that recurrence is common and preventive measures are key.

✅ Model Answer: • Indications for oral therapy:
- Extensive disease (involving >50% of the trunk).
- Recurrent disease (frequent episodes).
- Topical treatment failure (poor response or non-compliance).
- Immunocompromised patients (more severe and persistent).
- Cosmetic preference (patient prefers oral over topical).
• Oral options: Fluconazole (300 mg weekly x 2-4 weeks), itraconazole (200 mg daily x 5-7 days).
• Monitoring: Liver function tests if prolonged therapy (itraconazole).

✅ Model Answer: • Tinea versicolor:
- Hypopigmented or hyperpigmented macules with fine scale.
- Lesions are on the trunk/neck (sebaceous areas).
- KOH shows "spaghetti and meatballs" (hyphae + spores).
- Wood lamp: yellow-gold fluorescence.
- Caused by Malassezia furfur.
- Responds to antifungal therapy.
• Vitiligo:
- Complete depigmentation (milk-white) with no scale.
- Lesions are well-demarcated, often symmetric.
- No fungal elements on KOH.
- Wood lamp: chalk-white fluorescence (enhanced contrast).
- Autoimmune etiology (melanocyte destruction).
- No response to antifungals; treated with topical steroids, calcineurin inhibitors, phototherapy.

✅ Model Answer: • "Your child has a common fungal infection called tinea versicolor. It is caused by a yeast that naturally lives on the skin, but it overgrows in warm, humid conditions."
• "The rash is not serious and is not contagious. It causes light-colored patches on the skin, especially on the neck, chest, and back."
• "We will treat it with an antifungal cream, shampoo, or oral medication. The scaling will clear up quickly, but the light patches may take weeks to months to repigment."
• "The patches may become more noticeable after sun exposure because they do not tan. This is normal."
• "To prevent recurrence, your child can use a medicated shampoo (selenium sulfide or ketoconazole) once a week, especially during hot and humid months."
• "Encourage your child to wear loose-fitting cotton clothes and avoid excessive sweating."

✅ Model Answer: • Selenium sulfide 2.5% (shampoo): A topical antifungal and keratolytic agent.
• Mechanism: It has anti-Malassezia activity and helps remove the scale (keratolytic effect).
• Application: Apply to affected areas, leave for 10 minutes, then rinse thoroughly. Repeat daily for 1-2 weeks.
• Maintenance: Once-weekly application can prevent recurrence (especially during warm months).
• Advantages: Inexpensive, over-the-counter, effective for mild-to-moderate disease.
• Side effects: Contact dermatitis, irritation (especially in sensitive skin).

✅ Model Answer: • Ketoconazole 2% (shampoo or cream): An imidazole antifungal.
• Mechanism: Inhibits ergosterol synthesis (cell membrane) of Malassezia.
• Topical use: Apply shampoo to affected areas, leave for 5 minutes, then rinse. Daily for 3 days.
• Single-dose application: One application may be sufficient in some cases.
• Oral ketoconazole: 400 mg single dose is effective but less commonly used due to liver toxicity concerns. Fluconazole is preferred for oral therapy.
• Advantages: Effective, well-tolerated, available OTC in many countries.