This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and electrolytes, Subject name: Medicine
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) causes 
Select and explain. 
A. Euvolemic hyponatremia, B. Hypovolemic hyponatremia, C. Hypervolemic hyponatremia, D. Hypernatremia
A: Euvolemic hyponatremia
Answer: A: Euvolemic hyponatremia 
Explanation: The syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of euvolemic hyponatremia. Glucocoicoid deficiency, Hypothyroidism, Stress, Drugs are other causes of euvolemic hyponatremia. Common causes of SIAD include pulmonary disease (e.g., pneumonia, tuberculosis, pleural effusion) and central nervous system (CNS) diseases (e.g., tumour, subarachnoid haemorrhage, meningitis). SIAD also occurs with malignancies, most commonly with small-cell lung carcinoma (75% of malignancy-associated SIAD) SIAD is also a frequent complication of ceain drugs, most commonly the selective serotonin reuptake inhibitors (SSRIs). Ref: Harrison 19e pg: 300