Guillain–Barré syndrome hyponatremia: is it SIADH or pseudohyponatremia?

Approximately 5% of hospitalized patients with Guillain–Barré syndrome (GBS) experience SIADH; but pseudohyponatremia has also been reported in patients treated with IVIG. We present a case of a 51-year-old male with GBS who developed acute hyponatremia the day after initiation of IVIG; his sodium levels began to improve within 24 h of completion of IVIG. Differentiating between pseudohyponatremia caused by the IVIG treatment and SIADH caused by GBS was the key to successfully treating this patient. This case exemplifies the importance of pursuing further studies to determine the exact cause of hyponatremia in GBS in order to prevent further neurologic damage to the patient.