USMLE Step 2 CK Practice Test 2025 – Complete Exam Prep

The presence of pinkish, scaling lesions on the chest and back that exhibit a "spaghetti-and-meatballs" appearance in a KOH (potassium hydroxide) preparation is characteristic of Tinea Versicolor, also known as Pityriasis Versicolor. This fungal infection is caused by Malassezia yeast, which is a part of the normal skin flora.

In Tinea Versicolor, the KOH prep reveals hyphal elements and yeast forms that resemble spaghetti (hyphae) and meatballs (yeast cells) microscopically. This specific appearance helps distinguish Tinea Versicolor from other dermatological conditions. The scaling lesions are often hypopigmented or hyperpigmented because the fungus interferes with the normal production of melanin in the skin, leading to areas of altered pigmentation.

In contrast, other conditions like Tinea Corporis (ringworm) would typically present with annular, well-defined lesions and would not produce the same characteristic KOH prep findings. Psoriasis is usually identified by silvery scales and a different histological profile, and a Viral Exanthem often presents as a diffuse rash without the characteristic scaling seen in Tinea Versicolor.