## **Core Concept**
The clinical presentation described for the 7-year-old boy—boggy swelling of the scalp with multiple discharging sinuses, cervical lymphadenopathy, and easily pluckable hair—strongly suggests **Keratitis or more likely a condition known as Favus**, which is a chronic and contagious fungal infection of the scalp caused by *Trichophyton schoenleinii*. This condition leads to the formation of a boggy mass (favus) and is characterized by the presence of multiple discharging sinuses.

## **Why the Correct Answer is Right**
The diagnosis of favus or a similar fungal infection of the scalp, given its chronic nature and specific symptoms like boggy swelling, discharging sinuses, and easily pluckable hair, is best confirmed through **microscopic examination and culture**. A diagnostic tool that directly helps in identifying the causative fungus is by examining **hair samples under a microscope for the presence of fungal spores** or by performing a **culture of the fungal pathogen**. The description best aligns with taking a **scalp scraping for KOH preparation and culture**, which helps in identifying the fungus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While imaging might provide some information on the extent of tissue involvement, it does not directly lead to the identification of the causative agent in infections like favus.
- **Option B:** Biopsy might provide some information but is not the first line or most direct method for diagnosing fungal infections of the scalp like favus.
- **Option C:** This option seems to be missing but presumably, if it suggested a treatment approach rather than a diagnostic one, it would be incorrect because the question specifically asks for a diagnostic step.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in this scenario is to remember that **favus and other fungal scalp infections are highly contagious and require prompt diagnosis and treatment** to prevent spread and complications. A simple, non-invasive diagnostic test like a **KOH preparation** can quickly help confirm the diagnosis by showing characteristic fungal elements.

## **Correct Answer:** . Scalp scraping for KOH preparation and culture