Differential Diagnosis
- Single most likely diagnosis:
- Tuberculous lymphadenitis: The presence of a non-tender anterior neck fluctuant mass, a positive PPD (4mm is considered positive in certain contexts, especially in children), and biopsy findings of giant cells are highly suggestive of tuberculous lymphadenitis. The history of exposure to potential sources of tuberculosis (e.g., grandparents who might have been exposed or have traveled) could support this diagnosis.
- Other Likely diagnoses:
- Cat-scratch disease: Although the child was at the grandparents' farm, playing with a cat could still be a possibility. The presence of a fluctuant mass and giant cells on biopsy could be consistent with cat-scratch disease, caused by Bartonella henselae.
- Mycobacterium avium complex (MAC) infection: This could be considered given the child's exposure to the farm environment, where they might have come into contact with contaminated water or soil. MAC infections can cause lymphadenitis with similar clinical and histopathological findings.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Lymphoma: Although less likely, lymphoma could present with lymphadenopathy and should be considered, especially if the child has systemic symptoms or if the lymph node biopsy shows atypical cells.
- Sarcoidosis: This is a rare condition in children but can cause lymphadenopathy with non-caseating granulomas (giant cells). It's essential to consider sarcoidosis due to its potential for multi-organ involvement.
- Rare diagnoses:
- Toxoplasmosis: This parasitic infection can cause lymphadenopathy, but it's less common and typically associated with other symptoms like fever and fatigue.
- Histoplasmosis: Exposure to bird or bat droppings could lead to histoplasmosis, which can cause lymphadenitis. However, this would be less likely without specific exposure history or systemic symptoms.
- Brucellosis (despite the negative titre): Although the Brucellosis titre is negative, it's essential to consider the possibility of a false-negative result, especially if the child was exposed to unpasteurized dairy products or had contact with infected animals. However, the clinical presentation and biopsy findings are not strongly suggestive of brucellosis.