Castleman disease is a rare lymphoproliferative disorder with unicentric and multicentric forms. It can mimic tuberculosis, lymphoma, systemic lupus erythematosus and other inflammatory diseases, making diagnosis challenging. Excess interleukin-6 activity is central to many systemic manifestations, particularly in idiopathic multicentric Castleman disease. A 20-year-old male presented with a slowly enlarging left cervical swelling for two years, with rapid progression over three months, evening low-grade fever, night sweats, anorexia and 8-10 kg weight loss. Examination revealed a hard, non-tender left cervical mass. CRP and IL-6 were elevated, while autoimmune, HIV, HHV-8, viral and tuberculosis workup was negative. CT showed a left anterior cervical chain mass with hilar and inguinal lymph node involvement. Excision biopsy demonstrated hyaline vascular Castleman disease morphology. The clinicoradiological and histopathological findings supported multicentric Castleman disease, hyaline vascular type. Because siltuximab was not locally available, the patient was treated with tocilizumab 8 mg/kg intravenously every two weeks, along with tapering corticosteroids. After six doses, he achieved complete remission. This case highlights that Castleman disease should be considered in chronic cervical lymphadenopathy with constitutional symptoms after excluding infection, autoimmune disease and malignancy. Early excision biopsy, systemic staging and targeted anti-IL-6 therapy can lead to excellent clinical response in HHV-8-negative multicentric disease.