Idiopathic Multicentric Castleman Disease Mimicking Sepsis and Autoimmune Disease in a Caribbean Patient

Idiopathic multicentric Castleman disease (iMCD) is a rare cytokine-driven lymphoproliferative disorder characterised by systemic inflammation, generalised lymphadenopathy, and multiorgan involvement.Its clinical presentation may closely mimic sepsis, autoimmune disease, and other inflammatory disorders, creating a significant diagnostic challenge, particularly in resource-limited settings.We describe a 73-yearold Caribbean woman who presented with approximately one month of fever, progressive unintentional weight loss, profound fatigue, bilateral lower-limb oedema, and cutaneous hyperpigmentation.She was initially evaluated for sepsis and treated with broad-spectrum antibiotics for one week; however, microbiological investigations were negative, and there was no significant clinical improvement.Laboratory investigations demonstrated marked systemic inflammation, anaemia, thrombocytopenia, leukopenia, and hypoalbuminaemia.Computed tomography revealed generalised lymphadenopathy and splenomegaly, with additional thoracic findings including interstitial lung changes and small pleural and pericardial effusions.Autoimmune serology showed isolated ANA positivity, with dsDNA, ENA subtypes, rheumatoid factor, anti-CCP, and ANCA all negative -not meeting criteria for an alternative connective tissue disease.Excisional lymph node biopsy demonstrated atrophic germinal centres, expanded mantle zones, and polyclonal plasmacytosis, while testing for human herpesvirus-8 and immunoglobulin G4 was negative, confirming iMCD.A concurrent breast mass identified on imaging was biopsied and showed features in keeping with iMCD rather than malignancy.Treatment included corticosteroids, hydroxychloroquine, and azathioprine, with supportive therapy.During a severe inflammatory flare six weeks after admission, tocilizumab produced transient clinical and biochemical improvement, but she developed pruritus, angioedema, and shortness of breath during infusion; thus, ongoing biologic therapy was not continued.She has since been followed for approximately 19 months with a relapsing course managed through sequential steroid-sparing agents, with improved fatigue, weight gain, and improved quality of life despite residual cutaneous changes.This case highlights the importance of considering iMCD in patients with persistent systemic inflammation, generalised lymphadenopathy, cytopenias, and a negative infectious work-up and non-lupus-specific autoimmune profile, and illustrates the practical challenges of sustaining guideline-directed biologic therapy in a resource-limited Caribbean setting.