Differential Diagnosis for Chronically Ventilator-Dependent 80-Year-Old Woman with Chronic Hyponatremia
- Single Most Likely Diagnosis
- Hypothyroidism: The significant increase in TSH (from 5 to 25) and decrease in free T4 (from 20 to 14) over a short period suggests inadequate thyroid hormone replacement, leading to hypothyroidism. This condition can cause hyponatremia due to decreased free water clearance and increased ADH secretion.
- Other Likely Diagnoses
- Adrenal Insufficiency: Although less likely, adrenal insufficiency can cause hyponatremia and could be considered, especially if there are other signs such as hypotension or hyperkalemia. However, the primary abnormality here seems to be related to thyroid function.
- SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion): This condition can occur in the context of chronic illness and ventilation, leading to hyponatremia. However, the recent change in thyroid function tests suggests that hypothyroidism is a more direct cause.
- Do Not Miss Diagnoses
- Myxedema Coma: Although rare and typically presenting with more severe symptoms, myxedema coma is a life-threatening condition that can occur in untreated or severely hypothyroid patients. It's crucial to consider this diagnosis, especially given the significant increase in TSH and the patient's age and ventilator dependence.
- Acute Adrenal Crisis: While less directly related to the thyroid function abnormalities, an acute adrenal crisis can present with hyponatremia among other symptoms and is life-threatening if not promptly treated.
- Rare Diagnoses
- Sheehan Syndrome: A rare condition involving postpartum necrosis of the pituitary gland, which could potentially lead to both hypothyroidism and adrenal insufficiency. However, given the patient's age and history of thyroidectomy, this is less likely.
- Central Hypothyroidism: Although the patient has a history of thyroidectomy and is on levothyroxine, central hypothyroidism due to a pituitary issue could be considered if the thyroid hormone replacement is thought to be adequate but the patient remains hypothyroid. This would typically require further evaluation, including assessment of other pituitary hormones.