Possible Diagnosis: Pityriasis Versicolor (Tinea Versicolor)
The most likely diagnosis is pityriasis versicolor (tinea versicolor), a superficial fungal infection caused by Malassezia furfur, which characteristically presents as hyperpigmented or hypopigmented flat, round patches on the trunk and neck that worsen with itching at night. 1
Clinical Features Supporting This Diagnosis
The description of small, round, flat lesions with darker pigmentation on a Black patient's chest and neck is classic for pityriasis versicolor, which commonly presents as hyperpigmented patches in darker-skinned individuals 1
The distribution pattern (chest, neck, back of neck) is typical for tinea versicolor, as this fungal infection predominantly affects the trunk and proximal extremities 1, 2
Mild pruritus that worsens at night is consistent with this diagnosis, though itching is typically mild to moderate in pityriasis versicolor 1
The 3-day timeline suggests an acute awareness of a chronic condition rather than a new infection, as tinea versicolor is often present for weeks before patients notice it 1
Why Selsun Blue Was Mentioned
The patient's use of Selsun Blue (selenium sulfide) is actually appropriate, as selenium sulfide 1-2.5% is a traditional and effective treatment for pityriasis versicolor 1, 2, 3
However, selenium sulfide requires proper application technique: it should be applied to the entire affected area for 5-15 minutes daily for 18 days, not just used as a regular shampoo 3
The patient may have been attempting self-treatment, which suggests they or a family member suspected a fungal condition 2
Diagnostic Confirmation Needed
Direct microscopic examination with KOH preparation showing "spaghetti and meatballs" appearance (hyphae and spores) confirms the diagnosis 2, 4
Wood's lamp examination may show yellow-gold fluorescence, though this is not always present 3
Clinical diagnosis alone is often sufficient when the characteristic appearance and distribution are present 1, 2
Alternative Diagnoses to Consider (Less Likely)
Post-inflammatory hyperpigmentation could present similarly but would require a preceding inflammatory condition and wouldn't typically itch 5, 6
Atopic dermatitis is unlikely given the flat (not raised) nature of lesions, lack of flexural involvement, and absence of dry skin or family history of atopy 5, 6
Secondary bacterial infection is not suggested by the absence of crusting, weeping, or erosions 7, 6
Treatment Recommendations
Continue selenium sulfide 2.5% (Selsun Blue), but apply correctly: lather on affected areas and leave for 10-15 minutes before rinsing, once daily for 2-3 weeks 2, 3, 8
Alternatively, ketoconazole 2% shampoo once weekly for 3 weeks has a 95% cure rate and may be more convenient 2
Treat the entire trunk and proximal extremities, not just visible lesions, as subclinical infection is common 1, 3
Warn the patient that pigmentation changes may persist for months after successful fungal eradication, which is normal 1
Important Caveats
Recurrence is extremely common (up to 60-80% of patients) even after successful treatment, so prophylactic monthly applications may be needed 1, 2
The darker pigmentation will not resolve immediately with antifungal treatment—it may take 6-12 months for skin color to normalize 1
If no improvement after 3-4 weeks of proper treatment, consider alternative diagnoses or refer to dermatology 2, 4