What are common causes of SIADH?

The correct answer is that common causes of SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion) include malignant tumors and head injuries. In SIADH, there is an inappropriate secretion of the antidiuretic hormone (ADH), leading to water retention and diluted serum sodium levels. Various malignancies, especially small cell lung cancer, can produce ectopic ADH, resulting in SIADH. Additionally, head injuries such as traumatic brain injury or subarachnoid hemorrhage can disrupt normal hypothalamic function, leading to the abnormal secretion of ADH.

The other options involve factors that are not direct causes of SIADH. While excessive fluid intake can exacerbate the condition, it is not considered a primary cause. Low dietary sodium is a consequence rather than a cause of SIADH, as the syndrome leads to hyponatremia due to water retention. Type 1 diabetes is unrelated to SIADH; it pertains to insulin deficiency and does not influence ADH secretion or function. Understanding the underlying causes of SIADH is crucial for appropriate management and treatment of the condition.