Which clinical finding is more indicative of infectious mononucleosis compared to streptococcal pharyngitis?

The presence of posterior cervical lymphadenopathy is indeed more indicative of infectious mononucleosis than of streptococcal pharyngitis. In infectious mononucleosis, which is often caused by Epstein-Barr virus (EBV), the hallmark clinical features include extreme fatigue, fever, pharyngitis, and notable lymphadenopathy. Particularly, the posterior cervical lymph nodes are frequently enlarged and tender in cases of mononucleosis, a manifestation that is less commonly seen in streptococcal pharyngitis.

In contrast, streptococcal pharyngitis typically presents with anterior cervical lymphadenopathy. Therefore, the distinction between the two conditions can often be made based on the location of lymph node involvement. Other symptoms like fever and rash may occur in both conditions but are not exclusive to either one, making lymphadenopathy a key differentiating factor.

Thus, identifying posterior cervical lymph node involvement strongly points towards infectious mononucleosis and serves as a clinical indicator in differentiating it from other types of pharyngitis, including that caused by streptococcal infections.