An adult presents with oval scaly hypopigmented macule over the chest and the back. The diagnosis is
**Core Concept**
The adult presentation with an oval scaly hypopigmented macule over the chest and back suggests a dermatological condition involving epidermal barrier disruption, immune system involvement, or fungal infection, which can be distinguished based on the patient's clinical features and epidemiological risk factors.
**Why the Correct Answer is Right**
The diagnosis is most likely **Pityriasis versicolor (Malassezia folliculitis)**, caused by the overgrowth of the yeast Malassezia, which thrives in the warm, humid environment of the skin folds. The scaly hypopigmented macules are a result of the yeast's interaction with the host's skin cells, leading to abnormal melanin production and skin barrier disruption. The condition is more common in individuals with oily skin, particularly in tropical regions.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Pityriasis alba** is a condition characterized by oval-shaped, scaly, hypopigmented patches on the face, but it is more common in children and typically does not involve the back.
* **Option B:** **Pityriasis rosea** presents with a herald patch followed by a secondary eruption of oval-shaped, scaly patches, often on the trunk and proximal limbs, but the patches are typically erythematous rather than hypopigmented.
* **Option C:** **Pityriasis lichenoides** is a chronic skin condition characterized by small, scaly, erythematous papules, often on the trunk and limbs, but it does not typically present with large, oval-shaped, hypopigmented macules.
**Clinical Pearl / High-Yield Fact**
To differentiate between Pityriasis versicolor and other dermatological conditions, remember the "A" in **A**spergillus (a type of fungus) doesn't cause **V**ersicolor (Pityriasis versicolor), which is actually caused by **M**alassezia (a type of yeast).
**Correct Answer: C. Pityriasis lichenoides**