A Case of Relapsing Hyponatremia Associated with Fungal Sinusitis

Introduction: Hyponatremia is one of the most common electrolyte abnormalities in clinical practice. Syndrome of inappropriate antidiuretic hormone (SIADH) accounts for the majority of hyponatremia cases. In some cases, it may be challenging to find an underlying etiology. Case Presentation: We present a 76-year-old male patient with complaints of altered consciousness, disorientation, and relapsing hyponatremia. The final evaluation of hyponatremia showed a diagnosis of SIADH. As the patient's hyponatremia was unresponsive to fluid restriction, tolvaptan was started at a 7.5 mg/day dose. Following detailed investigations to find an etiology of SIADH, sphenoidal sinusitis was detected, and sinus biopsy culture yielded Aspergillus flavus/oryzae. Voriconazole (IV 6 mg/kg loading followed by 4 mg/kg) commenced, and tolvaptan was discontinued during the follow-up. Conclusion: Fungal infections should be kept in mind after excluding other causes of central nervous system-related hyponatremia in immunocompetent individuals without alarming symptoms suggestive of malignancy.