Hyponatremia in a Patient with Amyotrophic Lateral Sclerosis: A Case Report

Case Diagnosis: The patient was diagnosed with ALS and subsequently developed hyponatremia, likely attributed to SIADH.

Case Description or Program Description: The patient was found to have hyponatremia during admission to rehabilitation hospital following a diagnosis of amyotrophic lateral sclerosis, confirmed with electrodiagnostic studies. The patient was prescribed Riluzole but was choosing not to take the medication for personal reasons. Lab results showed a decline in sodium levels from 136 mmol/L on admission to 126 mmol/L without symptoms of hyponatremia. Fluid restriction of 1.5 liters daily was initiated. Sodium then dropped further to 124 mmol/L. Urine studies were assessed and demonstrated a urine sodium of 34 mmol/L and osmolality of 804 mOsm/Kg. The patient remained asymptomatic despite the decline in serum sodium.

Nephrology proposed SIADH and recommended stricter fluid restriction of 1.2 liters daily and 1 gram sodium chloride tablets twice daily. Sodium improved to 127 mmol/L the following day. The patient was discharged with a sodium level of 129 mmol/L, instructions to continue sodium tablets and fluid restriction, and to repeat lab work every 48 hours.

Setting: Inpatient Rehabilitation Hospital & Outpatient Setting

Assessment/Results: Within a week of discharge, the patient’s sodium levels returned to within normal limits (135 mmol/L) and remained within normal limits thereafter. Further developments will be discussed.

Discussion (relevance): To our knowledge, this is one of the few reported cases of SIADH occurring in the context of ALS without the use of riluzole, which is known to cause hyponatremia. In the setting of a life-altering diagnosis such as ALS, utilizing a non-aggressive approach (i.e, fluid restriction and sodium chloride tablets) to address this issue could prevent further distress to patients and their families.

Conclusions: Hyponatremia can occur in the context of ALS, even without the use of riluzole. It is important to monitor patients who have ALS for electrolyte imbalances.