Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): This condition is commonly associated with meningitis, especially when caused by bacterial or viral infections. The inflammation can lead to the inappropriate secretion of ADH, resulting in water retention and hyponatremia.

Cerebral Salt Wasting (CSW): Although less common than SIADH, CSW can occur in the context of meningitis, particularly when there is significant cerebral inflammation. It leads to renal loss of sodium, resulting in hyponatremia.
Adrenal Insufficiency: Infections like meningitis can precipitate adrenal crisis, especially in individuals with pre-existing adrenal dysfunction. Adrenal insufficiency can cause hyponatremia due to the lack of aldosterone, leading to impaired sodium retention.

Pituitary Apoplexy: Although rare, pituitary apoplexy can present with sudden onset of headache, meningismus, and hyponatremia due to acute loss of pituitary function, including ADH deficiency or excess. Missing this diagnosis could be fatal due to the potential for rapid progression and the need for urgent intervention.
Subarachnoid Hemorrhage: This condition can mimic meningitis and is associated with hyponatremia, often due to SIADH or CSW. It's critical to distinguish between these conditions due to the vastly different management strategies.

Thyroid Dysfunction: Both hypothyroidism and hyperthyroidism can be associated with hyponatremia, though they are less common causes in the context of meningitis. However, in patients with a history of thyroid disease, this could be a contributing factor.
Nephrogenic Syndrome of Inappropriate Antidiuresis (NSIAD): A rare condition that can cause hyponatremia due to an inappropriate response to ADH at the renal level, potentially seen in the context of meningitis, though extremely uncommon.