Prevalence and Aetiology of Syndrome of Inappropriate Antidiuretic Hormone in Hyponatraemia: A Cross-sectional Study

Introduction: Hyponatraemia is a frequently occurring electrolyte abnormality. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is one of the common causes of hyponatraemia. SIADH is a disorder of impaired water excretion caused by the inability to suppress the secretion of Antidiuretic Hormone (ADH). The importance of determining the cause of hyponatraemia as SIADH is not only to seek the aetiology of SIADH but also to treat appropriately. Aim: To determine the prevalence of SIADH in patients with hyponatraemia and its causes in these patients. Materials and Methods: A cross-sectional study was conducted in the Department of General Medicine at Jubilee Mission Medical College and Hospital, Thrissur, Kerala, India. The study duration was one year and six months, from December 2014 to June 2016. A total of 100 individuals over the age of 18, who were admitted with serum sodium levels under 135 mEq/L, were chosen. Data on the causes of hyponatraemia and SIADH, laboratory evaluations, and assessments based on SIADH criteria were gathered using a structured proforma. The primary outcome variables included the aetiology of SIADH and the causes of hyponatraemia. Frequency and percentages were used to represent the data. The data were analysed using MS Excel. Results: Among 100 patients, the maximum number of patients with hyponatraemia were in the 59-78 years age group. Fortytwo (42) had severe hyponatraemia (Na < 120 mmol/L). The most common cause of hyponatraemia was drug intake (diuretics + antihypertensives), which constituted 42 (42%) of the total 100 patients, followed by SIADH in 33 (33%) patients. Among the aetiologies of SIADH, cerebrovascular accident was the most common (9/100), followed by pneumonia and Selective Serotonin Reuptake Inhibitors (SSRIs) in five patients each. Among the non neurological symptoms, vomiting was the most common symptom in 28 (28%) patients, followed by lethargy in 15 (15%). Among the neurological symptoms associated with hyponatraemia, confusion was the predominant one seen in 10 (10%) patients, followed by drowsiness in 7 (7%). Conclusion: SIADH is an important cause of hyponatraemia with a high prevalence. The prevalence of SIADH in hyponatraemic patients was 33%. Among the aetiologies of SIADH, cerebrovascular accident was the most common.