Final answer:
Epitrochlear lymphadenopathy is pathognomonic for cat-scratch disease, caused by the bacterium Bartonella henselae, which involves swelling of lymph nodes around the elbow.
Step-by-step explanation:
Epitrochlear lymphadenopathy is pathognomonic for certain conditions, acting as a distinguishing characteristic of a disease. Among the options provided, cat-scratch disease, caused by the bacterium Bartonella henselae, is particularly noteworthy for causing lymphadenopathy in the areas proximal to where the infection is introduced, including the epitrochlear nodes around the elbow. This contrasts with conditions such as infectious mononucleosis, which is usually associated with generalized lymphadenopathy but not specifically epitrochlear lymphadenopathy. Infectious mononucleosis is a common and mild infection caused by Epstein-Barr virus (HHV-4) or cytomegalovirus (HHV-5) and typically presents with symptoms like sore throat, fever, fatigue, and swollen lymph nodes.