**Question:** A child is brought to you because of perianal itching, which has been disturbing the child's sleep. Examination reveals scaly skin in the perianal region. You instructs the parents to place transparent tape on the perianal region the next morning, and then return to you. Next day the tape is transported to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. Most likely cause?

A. Malassezia furfur infection
B. Tinea cruris
C. Tinea anogenitalis
D. Pediculosis pubis

**Core Concept:** Diagnosis of dermatological conditions by tape-stripping technique

**Why the Correct Answer is Right:**

The correct answer is D. Pediculosis pubis, also known as crabs or scabies, is a parasitic infestation caused by the human body louse, Pediculus humanus corporis. In this case, the tape-stripping technique is applied to identify the eggs (scuticocontractus) which are flattened along one side, as they are laid by the female louse to ensure proper feeding and development of the larvae.

**Why Each Wrong Option is Incorrect:**

A. Malassezia furfur infection (A) is a fungal infection caused by Malassezia species, commonly seen in patients with impaired skin barrier function, like those with atopic dermatitis or psoriasis. The eggs are typically round and non-flattened.

B. Tinea cruris (B) is a fungal infection caused by Trichophyton species. It affects the groin area and presents with redness, itching, and scaling. Tinea cruris does not involve eggs, making it an incorrect choice.

C. Tinea anogenitalis (C) is a fungal infection caused by Trichophyton species affecting the genital area. Similar to Tinea cruris, Tinea anogenitalis does not involve eggs, making it an incorrect choice.

**Clinical Pearl:**

The tape-stripping technique is a useful diagnostic tool in dermatology, particularly for identifying parasitic infections. By examining the tape, clinicians can identify the characteristic eggs of the parasites and differentiate them from other skin conditions.

**Core Concept:** Tape-stripping technique in dermatology

In tape-stripping, a small piece of adhesive tape is applied to the skin and then removed, and the adherent stratum corneum is examined under a microscope. This technique is particularly useful for identifying skin parasites, such as pediculosis (head lice or body lice), scabies, and certain skin infections (e.g., pediculosis capitis). By examining the tape, clinicians can identify the eggs (nits) of the parasites, allowing for a definitive diagnosis.