Viral Pharyngitis: This is often the most common cause of enlarged lymph nodes in the neck, accompanied by neck soreness. It is usually self-limiting and caused by viral infections such as mononucleosis or the common cold.

Bacterial Pharyngitis: Caused by bacteria like Streptococcus pyogenes, this condition can lead to swollen lymph nodes and neck pain. It requires antibiotic treatment.
Tuberculosis (TB): Although less common in some regions, TB can cause lymphadenopathy (enlarged lymph nodes) and is a significant consideration, especially in high-risk populations or areas with high TB prevalence.
Reactive Lymphadenitis: This is a non-specific response to infection or inflammation in the body, which can cause lymph nodes to become enlarged and tender.

Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can present with enlarged lymph nodes in the neck. Although less common, missing this diagnosis could have severe consequences.
Metastatic Cancer: Cancers from other parts of the body can metastasize to the lymph nodes in the neck, making this a critical diagnosis not to miss, especially in older adults or those with a history of cancer.
HIV Infection: Acute HIV infection can cause significant lymphadenopathy, and early diagnosis is crucial for treatment and management.

Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the lymph nodes, leading to their enlargement.
Castleman Disease: A rare disorder that involves an overgrowth of cells in the lymph nodes, which can cause them to become enlarged.
Kikuchi-Fujimoto Disease: A rare, self-limiting condition that causes lymph node enlargement, typically in the neck, and is more common in young women.

Each of these diagnoses has distinct implications for treatment and patient outcomes, emphasizing the importance of a thorough diagnostic workup.