A 10-yr-old boy presented with painful boggy swelling of scalp, multiple sinuses with purulent discharge, easily pluckable hair, and lymph nodes enlarged in occipital region. Which one of the following would be most help ful for diagnostic evaluation?
**Core Concept**
The presentation is suggestive of a scalp infection, specifically folliculitis or furuncles, which may have progressed to a more severe condition like carbuncles. The presence of painful boggy swelling, multiple sinuses, and purulent discharge points towards a bacterial infection involving the hair follicles.
**Why the Correct Answer is Right**
The most helpful diagnostic evaluation for this condition would be a Gram stain of the pus or discharge. This is because the Gram stain can quickly identify the type of bacteria responsible for the infection, which is crucial for guiding antibiotic therapy. The Gram stain differentiates between Gram-positive (blue-colored) and Gram-negative (red-colored) bacteria, which have different cell wall compositions. In this case, Staphylococcus aureus, a Gram-positive bacterium, is a common cause of scalp infections.
**Why Each Wrong Option is Incorrect**
**Option A:** Blood culture would be more relevant if there was suspicion of bacteremia or sepsis, which is not indicated in this case.
**Option B:** MRI or CT scan would be useful for assessing the extent of the infection or potential complications like abscesses, but would not provide a rapid diagnosis of the causative organism.
**Option C:** Skin biopsy would be more relevant for diagnosing conditions like acne, eczema, or other skin diseases, but would not be the first-line diagnostic test for a scalp infection.
**Clinical Pearl / High-Yield Fact**
In cases of scalp infections, always consider the possibility of Staphylococcus aureus as the causative organism, and obtain a Gram stain of the pus or discharge to guide antibiotic therapy.
**Correct Answer:** C.