Which cells are pathognomonic for Hodgkin's disease?

Reed-Sternberg cells are the hallmark cells associated with Hodgkin's lymphoma, which is a type of cancer that originates in the lymphatic system. The presence of these atypical cells is essential for the diagnosis of Hodgkin's disease and is considered pathognomonic, meaning that their detection is strongly indicative of this particular condition.

Reed-Sternberg cells are derived from B lymphocytes and are characterized by their large size, abundant cytoplasm, and typically bilobed or multinucleated appearance. These cells are not present in other types of lymphoma or hematological malignancies, which is what makes them a unique marker for Hodgkin's disease.

In contrast, the other options refer to cell types found in different contexts. Niemann-Pick cells are associated with a genetic disorder affecting lipid metabolism, reactive lymphocytes are typically seen in response to infections or inflammation, and flame cells are indicative of multiple myeloma. Therefore, Reed-Sternberg cells are specifically tied to Hodgkin's disease, distinguishing them as the correct answer to this question.