What symptom would differentiate Adult T-Cell Leukemia from Multiple Myeloma?

Adult T-Cell Leukemia (ATL) is associated with the presence of specific skin manifestations, including rashes, as a result of the proliferation of malignant T lymphocytes. This rash can appear as erythroderma or generalized dermatitis, which is a hallmark sign of ATL, distinguishing it from other hematologic malignancies.

In contrast, Multiple Myeloma primarily presents with symptoms related to bone marrow infiltration, such as bone pain, fatigue, and complications from hypercalcemia, but does not typically involve skin rashes. Fatigue in Multiple Myeloma can be attributed to anemia and other systemic effects, and bone pain often results from osteolytic lesions.

The presence of hyperkalemia is not a characteristic feature of either condition, making it less useful for differentiation. Therefore, the distinctive symptom of a rash in Adult T-Cell Leukemia serves as an important clinical clue that helps differentiate it from Multiple Myeloma, which lacks this dermatological involvement.