Differential Diagnosis for Unilateral Pre-auricular Lymphadenopathy

Single Most Likely Diagnosis

• Cat scratch disease: This is often the most common cause of unilateral pre-auricular lymphadenopathy, especially in children and young adults who have been exposed to cats. The disease is caused by Bartonella henselae, transmitted through scratches or bites from infected cats.

Other Likely Diagnoses

• Infectious causes (e.g., streptococcal or staphylococcal infections): These can cause lymphadenopathy due to localized infections such as impetigo, folliculitis, or parotitis.
• Dental infections: Infections of the teeth or gums can drain to the pre-auricular lymph nodes, causing lymphadenopathy.
• Viral infections (e.g., herpes simplex, varicella-zoster): These can cause localized lymphadenopathy, especially if there is a rash or lesion in the vicinity of the ear.

Do Not Miss Diagnoses

• Lymphoma: Although less common, lymphoma can present with unilateral lymphadenopathy and must be considered to avoid delayed diagnosis.
• Tuberculosis: TB can cause lymphadenopathy, and pre-auricular nodes can be involved, especially in endemic areas or in individuals with risk factors.
• Malignancy of the parotid gland or surrounding tissues: Tumors in the parotid gland or nearby structures can metastasize to pre-auricular lymph nodes.

Rare Diagnoses

• Sarcoidosis: This systemic disease can cause lymphadenopathy, including in the pre-auricular region, although it is less common.
• Kikuchi disease: A rare form of lymphadenitis that can present with unilateral lymphadenopathy, often accompanied by fever and night sweats.
• Kimura disease: A chronic inflammatory disorder that can cause lymphadenopathy and eosinophilia, more commonly seen in Asian males.

Each of these diagnoses has a different set of implications for patient management and outcome, emphasizing the importance of a thorough diagnostic evaluation.