Introduction Castleman disease, a rare lymphoproliferative disorder, is classified as unicentric (one lymph node) or multicentric (multiple regions). The latter include POEMS-associated, HHV-8-associated, and idiopathic type . POEMS syndrome features polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes. Approximately about 15 % of POEMS patients may have Castleman disease. Case Presentation A 28-year-old male from North Kerala, India, presented with pleuritic chest pain, worsening dyspnea, abdominal distention, intermittent fever, weight loss, and loss of appetite over months. He had a history of treated symmetrical polyarthritis. Examination revealed palpable bilateral lymph nodes, low normal BP, tachycardia, tachypnea, left tracheal deviation, stony dullness on lung percussion, and absent breath sounds bilaterally. Abdomen showed mild distention, palpable liver 2 cm below the costal margin, and dullness over Traube’s space. Neurological and musculoskeletal exams were unremarkable except for reduced CMAP amplitude in bilateral peroneal nerves on nerve conduction studies. Laboratory findings included positive ANA and Anti-TPO antibodies, suggesting autoimmune etiology. Liver function showed albumin-globulin reversal indicating chronic inflammation. Negative HHV-8 ruled out multicentric Castleman disease. Serum Immunoelectrophoresis showed normal pattern, but elevated kappa lambda light chain ratio (1.86). Elevated ferritin (572 ng/mL) and LDH (752 U/L) indicated cellular damage or inflammation. Pleural fluid analysis revealed exudative nature (4844 cells/cubic cm, pleural protein 4.1 g/dL, LDH 312 U/L). AFB and CBNAAT tests negative ruled out tuberculosis. ADA levels normal, cultures negative for bacterial infection. Cytology negative for malignancy; serology negative for HIV and other viruses. Imaging showed bilateral pleural effusion, lower lobe collapse, moderate pericardial effusion, and mild interstitial thickening. Excision biopsy of the right axillary lymph node showed features consistent with Castleman disease, specifically the hyaline vascular variant. Histopathological findings included distorted lymph node architecture, increased lymphoid follicles, atretic follicles, and sclerotic blood vessels penetrating the germinal centers (lollipop lesions). Mantle zones displayed concentric rings of small lymphocytes (onion skin arrangement). Discussion The diagnosis of POEMS syndrome in our patient is supported by the mandatory criteria of polyneuropathy and monoclonal gammopathy, confirmed by an abnormal light chain ratio. Additionally, Castleman disease fulfills a major criterion, while minor criteria such as pleural effusion, hepatomegaly, and thyroid endocrinopathy further contribute to the diagnosis.The patient was started on pulse corticosteroid therapy and low dose immunosuppressants that brought the patient into remission. This case highlights the importance of a comprehensive diagnostic approach and multidisciplinary management in addressing Castleman disease, hyaline vascular variant, with potential concurrent POEMS syndrome