Differential Diagnosis for Unilateral Non-Tender Cervical Lymph Node in a Thriving Child

Single Most Likely Diagnosis

• Reactive Lymphadenitis: This is the most common cause of cervical lymphadenopathy in children, often resulting from a viral upper respiratory tract infection. The lymph node's characteristics (unilateral, non-tender, discrete, mobile) and the child's thriving state support this diagnosis.

Other Likely Diagnoses

• Infectious Mononucleosis: Caused by Epstein-Barr virus, it can present with cervical lymphadenopathy, though it's often accompanied by systemic symptoms like fever and fatigue.
• Toxoplasmosis: A parasitic infection that can cause lymphadenopathy, usually without other significant symptoms in immunocompetent children.
• Cat Scratch Disease: Caused by Bartonella henselae, transmitted through cat scratches, leading to lymphadenopathy, often in the neck.

Do Not Miss Diagnoses

• Lymphoma: Although less common, lymphoma (Hodgkin or non-Hodgkin) is a critical diagnosis not to miss, as it requires prompt treatment. The presence of a large, persistent lymph node, even if non-tender, warrants further investigation.
• Tuberculosis: Especially in areas with high prevalence, TB can cause cervical lymphadenitis. It's crucial to consider this diagnosis due to its public health implications and the need for specific treatment.
• Metastatic Disease: Though rare in children, certain cancers like neuroblastoma, rhabdomyosarcoma, or thyroid cancer can metastasize to cervical lymph nodes.

Rare Diagnoses

• Kikuchi-Fujimoto Disease: A rare, self-limiting condition that causes lymphadenitis, more common in Asian populations.
• Kimura Disease: A chronic inflammatory disorder that can cause lymphadenopathy and eosinophilia, more prevalent in Asian males.
• Castleman Disease: A rare lymphoproliferative disorder that can present with lymphadenopathy, often with systemic symptoms.

Each of these diagnoses has distinct implications for management and prognosis, highlighting the importance of a thorough diagnostic workup based on clinical presentation and risk factors.