Utility of renal biopsy in differentiating idiopathic multicentric Castleman disease from IgG4-related disease

Idiopathic multicentric Castleman disease (iMCD) is a subtype of human herpesvirus type 8 (HHV-8)-related Castleman disease that causes multi-organ damage, including kidney damage due to polyclonal lymphoproliferation and interleukin (IL)-6-induced cytokine storm. However, its renal pathological findings are unclear. We report the case of a woman in her 80 s who was diagnosed with iMCD based on renal pathological findings. Five years ago, hypergammaglobulinemia was detected, and her renal function declined. Renal biopsy revealed plasma cells infiltrating the stroma. Immunostaining revealed numerous IgG4-positive plasma cells. The serum IgG4 level was high, and she was initially diagnosed with IgG4-related disease (IgG4-RD) and treated with steroids. However, the therapeutic effect was poor. On re-examination, computed tomography revealed lymphadenopathy around the aorta and spleen. Renal histopathology showed numerous IL-6-positive plasma cells. Anemia and C-reactive protein (CRP) positivity persisted despite steroid administration. HHV-8 was negative, and polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes syndrome was not suspected. Thus, iMCD was diagnosed. Based on previous reports, there is no significant difference in IgG4 levels between iMCD and IgG4-RD, and IgG4-positive plasma cell infiltrates were observed in iMCD-affected organs. Therefore, it may be difficult to distinguish iMCD from IgG4-RD. In this case, high-serum IL-6 and CRP were observed, which are usually not seen in IgG4-RD but are common findings in iMCD, leading to the diagnosis. Patients with deep lymphadenopathy may be diagnosed with iMCD based on renal pathological findings. Renal biopsy is recommended for patients with suspected iMCD and decreased renal function.

Epidemiology of Castleman Disease

Castleman disease is a rare entity, including unicentric Castleman disease (UCD), human herpesvirus-8 plus Castleman disease (HHV-8+MCD), and idiopathic multicentric Castleman disease (iMCD). UCD is the most common at 16 per million person years and occurs at every age. HHV-8+MCD incidence varies widely, mostly affecting human immunodeficiency virus-positive men. iMCD is likely a more heterogeneous disease with an estimated incidence of 5 per million person years. Improved definitions should improve understanding of the epidemiology of Castleman disease and its subtypes.

Immunodeficiencies with hypergammaglobulinemia: a review

Primary immunodeficiencies (PID) can present with recurrent infections, autoimmunity, inflammation, or malignancy and each of these conditions can be associated with elevated immunoglobulin. A high level of immunoglobulin G (IgG) is an uncommon finding, especially in pediatrics, and does not rule out primary immunodeficiency. Deficiencies in varied aspects of immune response have been described with high IgG. Reported PID conditions with elevated IgG include defects in humoral, cellular, and innate immunity. Some of these immunodeficiencies can have fatal outcomes, some require hematopoetic stem cell transplantation, and some require systemic medications. The mechanisms driving elevated IgG are not well understood, but in some cases abnormal cytokine production has been proposed. The evaluation of a patient with high IgG is guided by the patient's history and a physical examination, with special attention to autoimmunity in pediatrics and malignancy and liver disease in adults. In the setting of autoimmunity, chronic gastrointestinal disease, or chronic infections, the measurement of specific antibodies to evaluate the function of the IgG should be considered. An increased appreciation of elevation in IgG reflecting immune dysregulation may lead to earlier PID diagnoses.