An Unusual Cause of Acute Hyponatraemia

We present the case of an 81 year old man, admitted with ataxia and hyponatraemia. Biochemical analysis was suggestive of Syndrome of Inappropriate ADH (SiADH) which was initially attributed to a recent respiratory infection or treatment with omeprazole. Neurological symptoms worsened despite normalisation of sodium levels and further examination revealed generalised areflexia; subsequent investigation by the Regional Neurology team led to a diagnosis of Guillan Barre syndrome, and symptoms improved following treatment with Intravenous Immunoglobulin and prolonged in-patient rehabilitation. Guillan Barre syndrome is a recognised cause of SiADH and this case highlights the importance of considering this diagnosis along with full neurological examination when patients with hyponatraemia present with neurological symptoms.