SIADH Mimicking Drug-Induced Hyponatremia Secondary to Viral Pneumonia with Acute Ischemic Stroke: A Case Report

Abstract

Background: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a prevalent aetiology of hyponatraemia, frequently induced by drugs, pulmonary infections, or central nervous system disorders. It is challenging to differentiate between drug-induced hyponatraemia and SIADH caused by an infection, especially in the elderly with numerous other medical issues. Case Presentation: We present a case of a 68-year-old female with type 2 diabetes mellitus and hypertension, exhibiting high-grade fever, disorientation, and a dry cough. Laboratory investigations revealed hypotonic hyponatraemia, hypokalaemia and hypo-osmolality. The patient was on chlorthalidone and glimepiride, raising initial suspicion for drug-induced hyponatremia. Even after withdrawal of these medications and giving supportive care, sodium levels stayed low. Imaging showed pulmonary oedema, thickening of the interlobular septum, and lymphadenopathy in the mediastinum, which are all signs of viral pneumonia. On Day 6 acute ischaemic stroke was confirmed by an MRI. Careful fluid restriction, electrolyte supplementation, and carefully monitored low dose tolvaptan lead to normalization of serum sodium and neurological improvement Discussion: This case highlights the diagnostic complexity of hyponatraemia in elderly individuals undergoing polypharmacy. Persistent hyponatraemia, despite modifications in medication, requires assessment for infection-related SIADH. Severe and prolonged hyponatraemia heightens the risk of neurological complications, such as ischaemic stroke. Targeted therapy with vasopressin receptor antagonists, combined with multidisciplinary care, facilitated safe correction of sodium and clinical recovery. Conclusion: Drug-induced hyponatraemia can be clinically imitated by SIADH caused by viral pneumonia. To avoid complications and enhance results, early etiological re-evaluation, careful electrolyte monitoring, and tailored treatment—including safe tolvaptan use are crucial.