Low Sodium in Lymphoma: What it Means and What to Do

Low sodium (hyponatremia) in people with lymphoma can happen for a few different reasons, and the level of concern depends on how low the sodium is, how quickly it dropped, and what symptoms you have. In many cases, it is treatable and improves once the cause is addressed, but because severe or sudden drops can affect the brain, it’s wise to take it seriously and discuss it promptly with your oncology team.

Why lymphoma patients can develop low sodium

• Cancer-related SIADH: Some lymphomas, especially when they affect the brain or hypothalamus, can trigger the body to release too much antidiuretic hormone (ADH), causing water retention and dilution of sodium (this is called SIADH). SIADH has been reported as an initial sign in primary CNS lymphomas involving the hypothalamus. [PM10] This mechanism can lead to low sodium even when kidney function is normal. ^[1]

• Treatment-related effects: Certain chemotherapy drugs can contribute to SIADH or hyponatremia. Cyclophosphamide has documented risk of SIADH and hyponatremia, and the effect can be serious if not recognized early. ^{[2] [3]} Care teams often use hydration and monitoring protocols around high‑dose cyclophosphamide because of this known risk. ^[4] Some biologic or targeted agents used in T‑cell lymphomas have also reported hyponatremia among dose‑limiting toxicities in trials. [PM9]

• Other contributors: Nausea, vomiting, poor intake, excess free‑water drinking, and certain IV fluids can lower sodium, and these issues are common during cancer therapy. ^[5] CNS involvement can also cause inappropriate ADH secretion leading to hyponatremia, particularly with hypothalamic or brainstem disease. ^[1]

When to be concerned

• Mild, chronic hyponatremia (often sodium 130–134 mmol/L) may have subtle symptoms like fatigue or mild dizziness and is usually manageable with careful monitoring and addressing the cause. Your team may adjust fluids or medications and follow sodium trends. ^[5]

• Moderate to severe or rapidly falling sodium (typically <130 mmol/L, especially <125) can cause headache, confusion, nausea, vomiting, muscle cramps, seizures, or fainting. These symptoms warrant urgent medical attention because severe hyponatremia can lead to brain swelling if corrected incorrectly or left untreated. ^[6]

• Red flag symptoms: If you develop confusion, severe headache, repeated vomiting, seizures, or pass out, seek emergency care immediately; these can be signs of acute severe hyponatremia. ^[6]

Common symptoms to watch for

• Nausea, vomiting, loss of appetite, or dizziness, which can overlap with treatment side effects. If you feel dehydrated or dizzy, stand up slowly and discuss fluid guidance with your team. ^[7]
• Headache, trouble focusing, memory problems, confusion, muscle cramps, or balance changes. These can signal low sodium and should be reported promptly. ^[8]

How your team evaluates low sodium

• History and exam: They’ll ask about fluid intake, vomiting/diarrhea, medications, and any CNS symptoms. They’ll assess whether SIADH from disease or drugs, dehydration, or other causes are most likely. ^[5]
• Blood and urine tests: Serum sodium, osmolality, urine sodium/osmolality help distinguish SIADH (water retention with concentrated urine) from dehydration or other causes. Trends over time are important to guide safe correction. ^[5]
• Imaging when indicated: If symptoms suggest CNS involvement, brain imaging may be considered to evaluate hypothalamic or brain lesions that can cause SIADH. [PM10] ^[1]

Treatment depends on the cause and severity

• SIADH management: For stable cases, fluid restriction is often the first step; additional options include salt tablets, oral urea, or medications like vasopressin antagonists in selected cases. Addressing the underlying trigger such as adjusting chemotherapy or treating CNS disease is key. ^[5]
• Medication‑related hyponatremia: Your team may adapt drug dosing, timing, or hydration protocols around agents known to cause SIADH (for example, cyclophosphamide) and intensify lab monitoring during high‑risk periods. ^{[4] [2] [3]}
• Dehydration or losses: If vomiting or diarrhea is the driver, careful replacement with appropriate IV fluids and electrolytes is used, avoiding excess free water that can worsen sodium levels. ^[5]
• Severe or symptomatic hyponatremia: In emergencies, controlled correction with hypertonic saline may be used under close monitoring to avoid over‑rapid correction, which can harm the brain. This is managed in hospital with frequent checks. ^[6]

Practical tips for users with lymphoma

• Know your numbers: Ask for your recent sodium values and the plan if they trend down. Understanding whether your case is mild and stable or more acute helps tailor precautions. ^[5]
• Follow fluid guidance: If SIADH is suspected, stick to the fluid limits your team sets; drinking too much free water can worsen hyponatremia. If dehydrated from vomiting, ask what and how much to drink or when IV fluids are safer. ^{[7] [5]}
• Report symptoms early: Headache, confusion, repeated vomiting, or new seizures need urgent attention. Early care usually means safer, simpler fixes. ^[6]
• Medication awareness: If you’re scheduled for high‑dose cyclophosphamide or similar drugs, expect extra monitoring and ask about preventive steps, including hydration protocols and sodium checks. ^{[4] [2] [3]}

Bottom line

Low sodium in lymphoma can be due to the cancer itself (especially CNS involvement), the treatments, or common treatment side effects like vomiting and excess water intake. It’s often manageable, but sudden or severe drops are an urgent issue, so share symptoms quickly and follow your team’s fluid and monitoring plan. With timely evaluation and tailored treatment, most people improve safely. ^[1] [PM10] ^{[4] [2] [3] [5] [6]}