**Question:** Which of the following is a histological feature of Whipple's disease?

A. Enlarged macrophages with numerous inclusion bodies (PAS-positive, diastase-resistant)
B. Reduced bone marrow cellularity
C. Increased serum cholesterol levels
D. Hypertrophy of the spleen

**Core Concept:**
Whipple's disease is a rare, chronic, systemic disorder characterized by the inflammation of the small intestine and multiple organ involvement. It is caused by the bacterium Tropheryma whipplei. The disease was first described by Italian surgeon Giuseppe Giovanni Battista Negri in 1907, hence the term "Negri bodies" is sometimes used in reference to the characteristic histopathological findings.

**Why the Correct Answer is Right:**
In Whipple's disease, macrophages in the affected areas of the small intestine undergo marked hypertrophy and exhibit numerous, eosinophilic, PAS-positive (periodic acid-Schiff positive) inclusion bodies called "Trophozoites" or "Negri bodies." These bodies are diastase-resistant, meaning they can withstand the digestive enzymes in the pancreatic juice, which is why PAS staining is used.

**Why Each Wrong Option is Incorrect:**
A. Enlarged macrophages with inclusion bodies are present, but their properties (PAS-positive, diastase-resistant) differentiate the correct answer from this option.
B. Although bone marrow involvement is seen in Whipple's disease, reduced bone marrow cellularity is not a specific feature of the disease; it could be due to various other causes.
C. Increased serum cholesterol levels are not a consistent feature of Whipple's disease, as the primary pathology is in the small intestine.
D. Hypertrophy of the spleen is not specific to Whipple's disease; splenomegaly can occur in various medical conditions.

**Clinical Pearl:**
Whipple's disease is named after Dr. Alphonse Whipple, who described the disease in 1907. The disease is characterized by the presence of Tropheryma whipplei, a Gram-positive, aerobic, rod-shaped bacterium, found in the gastrointestinal tract. The disease is primarily diagnosed by histopathological examination of tissue samples, showing the characteristic inclusion bodies (Negri bodies) in macrophages.

**Why the Correct Answer is Right:**
In Whipple's disease, macrophages in the affected areas of the small intestine undergo marked hypertrophy and exhibit numerous, eosinophilic, PAS-positive, diastase-resistant inclusion bodies called "Trophozoites" or "Negri bodies." These bodies are PAS-positive due to the presence of glycogen in macrophages, and diastase-resistant due to the bacterium's resistance to pancreatic amylase enzyme.

**Why Each Wrong Option is Incorrect:**
A. Enlarged macrophages with inclusion bodies are present, but their properties (PAS-positive, diastase-resistant) differentiate the correct answer from this