Histiocytic necrotizing lymphadenitis with autoimmune encephalitis in a child: a case report.

Background: Histiocytic necrotizing lymphadenitis (HNL) is a rare benign self-limiting inflammatory disease that mainly affects young adults; however, the exact pathogenesis is unknown. A four-year-old child who was diagnosed with HNL combined with autoimmune encephalitis (AE) was admitted to Tongji Hospital of Huazhong University of Science and Technology. This study aimed to describe the clinical characteristics, laboratory tests, imaging findings, and treatment outcomes of this pediatric patient with HNL + AE. Case Description: A 4-year-old male child was admitted to our hospital after presenting with a neck mass persisting for over two months and a fever lasting five days. The initial symptom was fever accompanied by lymph node enlargement. The patient was diagnosed with HNL; however, the patient did not respond significantly to treatment, and he continued to have lymph node enlargement and intermittent fever. Some six months later, the patient developed neurological symptoms, including decreased voluntary activity, impaired speech, and reduced appetite. Subsequent serum testing yielded positive results for contactin-associated protein-2 (CASPR2), leading to a diagnosis of CASPR2 antibody-associated encephalitis. The final diagnosis was HNL + AE. The patient's condition improved after the corresponding treatment was administered. Subsequent follow-up examinations indicated no recurrence. Conclusions: This is the first documented case of HNL + AE in a pediatric patient exhibiting typical symptoms of fever, lymph node swelling, and pain, accompanied by acute neurologic symptoms, and an extended disease course. This report provides a reference for the diagnosis of HNL + AE in the future.