Viral Pharyngitis: This is often the most common cause of low-grade fever and lymphadenopathy, particularly in the context of a sore throat or recent upper respiratory infection. Justification: Viral infections are prevalent, and the combination of symptoms such as sore throat, low-grade fever, and lymphadenopathy (especially cervical) is typical for viral pharyngitis.

Infectious Mononucleosis (Mono): Caused by Epstein-Barr virus (EBV), it presents with fever, sore throat, and lymphadenopathy, particularly in the cervical region. Justification: The clinical presentation, especially in young adults, can strongly suggest mono, which is a common condition in this demographic.
Tuberculosis (TB): Can cause low-grade fever and lymphadenopathy, especially in the context of exposure or in endemic areas. Justification: TB is a significant public health concern and can present with systemic symptoms like low-grade fever and localized lymphadenopathy.
Toxoplasmosis: An infection caused by Toxoplasma gondii, which can lead to lymphadenopathy and sometimes a low-grade fever. Justification: This diagnosis is more likely in individuals who are immunocompromised or have been exposed to the parasite, often through undercooked meat or cat feces.

Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with lymphadenopathy and systemic symptoms like low-grade fever. Justification: Although less common, missing a diagnosis of lymphoma could have severe consequences, making it crucial to consider, especially in the absence of an obvious infectious cause.
HIV Infection: Acute HIV infection can present with fever, lymphadenopathy, and a rash, among other symptoms. Justification: The initial presentation of HIV can be nonspecific, and missing this diagnosis could lead to delayed treatment and significant morbidity.
Cat-Scratch Disease: Caused by Bartonella henselae, transmitted through cat scratches, leading to lymphadenopathy and sometimes low-grade fever. Justification: This condition is often overlooked but can cause significant morbidity if not treated appropriately.

Castleman Disease: A rare disorder that involves an overgrowth of cells in the body's lymph nodes, which can cause lymphadenopathy and systemic symptoms. Justification: This is a rare condition, but considering it in the differential is important for comprehensive evaluation, especially if common causes are ruled out.
Kikuchi-Fujimoto Disease: A rare, self-limiting condition that causes lymphadenopathy and fever, more common in young women. Justification: Although rare, it's an important consideration in the differential diagnosis of lymphadenopathy, particularly when other causes are not evident.
Sarcoidosis: An autoimmune disease that can cause lymphadenopathy and systemic symptoms, including fever. Justification: Sarcoidosis is a diagnosis of exclusion and should be considered when other causes of lymphadenopathy and fever are ruled out, especially in the context of other systemic symptoms or findings suggestive of the disease.