Unmasking the Enigma: A Case Report on Hyponatremia and Chimeric Antigen Receptor T Cell (CAR-T) Therapy in Mantle-Cell Lymphoma

Introduction: Chimeric Antigen Receptor T-cell (CAR-T) therapy is a new treatment for relapsed and refractory hematologic cancers. CAR-T cells are modified T-cells that express receptors targeting specific antigens on cancer cells, leading to their apoptosis and destruction. CAR-T therapy is associated with a unique adverse effects, such as cytokine release syndrome (CRS) and neurotoxicity. It can also cause electrolyte abnormalities, such as hyponatremia, hypophosphatemia, and hypokalemia. Here, we present a challenging case of hyponatremia following CAR-T therapy. Case Description: A 66-year-old male, known to have a history of Mantle cell lymphoma, diagnosed 8 months prior to presentation. Initially treated with R-CHOP, then underwent CAR-T therapy. Two months ago, he underwent Tecartus CAR-T therapy, which was complicated by grade 2 CRS. This was managed with tocilizumab, anakinra, and dexamethasone. He was noted with hyponatremia on outpatient labs, sodium levels at 119 meq/l. Upon presentation, he was completely asymptomatic. Exam showed orthostatic hypotension; treated with normal saline 0.9%, but sodium levels remained low. His serum osmolality was low(258mosm/kg), urine sodium was high(53meq/l), and urine osmolality was high(463mosm/l), suggesting syndrome of inappropriate antidiuretic hormone secretion. He was initiated on urea powder. Despite that, his sodium levels remained around 128meq/l. Considering the orthostatic vitals, bedside ultrasound findings revealed features consistent with a hypovolemic state, including an inferior vena cava diameter of 2.1cm and respiratory collapse exceeding 50%. Given these findings, he was given intravenous fluids which resulted in improvement in his levels, discharged with instructions to maintain a liberal intake of oral fluids. Follow-up labs showed sodium increase. Discussion: Hyponatremia, can complicate CAR-T treatment, and is frequently associated with CRS. The prompt identification and management of hyponatremia are crucial to ensure optimal outcomes for patients undergoing CAR-T therapy. CRS can be treated with immunosuppression. Treating hyponatremia in CAR-T-related cases poses challenges as one of the pathophysologies is volume depletion. Supportive measures with hydration, coupled with addressing potential underlying CRS, can aid in management.