Unraveling B Cell Lymphoma Presenting as AKI and Hypercalcemia in a Patient with BACH2 Variant and CVID

Introduction BACH2-related immunodeficiency and autoimmunity (BRIDA) increases the risk of developing B cell lymphoma. We present a case of a patient with a known history of common variable immunodeficiency (CVID) and BACH2 variant of uncertain significance, presenting with hypercalcemia and acute kidney injury (AKI), found to have T cell histiocyte-rich large B cell lymphoma of the spleen. Case Description 46-year-old male with CVID-like clinical picture with variant of uncertain significance in BACH2 (Combined Annotation Dependent Depletion [CADD] 25.2, allele frequency 2) and granulomatous-lymphocytic interstitial lung disease (GL-ILD), admitted for acute kidney injury with hypercalcemia. He is pancytopenic, hypercalcemic, with marked splenomegaly on CT. PET-CT showed retroperitoneal and iliac chain lymphadenopathy along with mixed changes of osseous/marrow lesions with new lesions in the thoracic spine and left mid femur. There is a notable improvement in GL-ILD on CT chest while the patient is on prednisone. Renal biopsy showed acute tubular injury with increased deposition of calcium phosphate, along with moderate interstitial fibrosis and tubular atrophy with mild fibrointimal thickening of arteries. No monoclonal protein detected in the serum, negative JC virus, BK virus, EBV, CMV, and HIV. Splenic biopsy showed B cell lymphoma with features of micronodular T cell/histiocyte-rich large B cell lymphoma of the spleen. Patient initiated on rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone treatment protocol. Discussion BACH2 is a regulator of T and B cell differentiation and maturation. The effect of BACH2 on T cells involves limiting the differentiation of regulatory T (Treg) cells, which aid in preventing autoimmunity. BACH2 mutations have been described in the literature in patients with CVID and autoimmunity, such as ulcerative colitis. Lymphoma can cause hypercalcemia, which can lead to acute kidney injury. This patient has a variant of uncertain significance in BACH2 with CADD 25.2, allele frequency 2. His clinical picture of CVID, acute kidney injury in the setting of hypercalcemia, and newfound B cell lymphoma of the spleen may be due to this variant of uncertain significance. Further studies need to be conducted to better understand this gene and its role in CVID and B cell lymphoma. Tabular data are included as downloadable supplement files.