Differential Diagnosis for 70 y/o Male with Post-Operative Symptoms

Single Most Likely Diagnosis

• Cerebral Salt Wasting (CSW) or Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): The patient's symptoms of hyponatremia, nausea, headache, and weight loss, particularly in the context of recent brain surgery, suggest a disorder of sodium and water balance. Both CSW and SIADH can occur post-operatively, especially after neurosurgical procedures, and can lead to hyponatremia.

Other Likely Diagnoses

• Postoperative Adrenal Insufficiency: The patient's symptoms of weight loss, anorexia, and hyponatremia could also suggest adrenal insufficiency, which might be secondary to the stress of surgery or potentially related to the meningioma or its treatment affecting the hypothalamic-pituitary-adrenal axis.
• Postoperative Hypopituitarism: Given the patient's recent neurosurgical procedure, hypopituitarism is a possibility, especially if the surgery affected the pituitary gland or its stalk. This condition could explain the hyponatremia, weight loss, and potentially the anosmia and taste perversion if the pituitary dysfunction affects hormone production related to these symptoms.
• Infection or Meningitis: Postoperative infection, including meningitis, could present with nausea, headache, and hyponatremia. Although less likely given the timeframe and specific symptoms, it remains a consideration.

Do Not Miss Diagnoses

• Pituitary Apoplexy: Although rare, pituitary apoplexy is a medical emergency that can occur post-operatively, especially if there was manipulation near the pituitary gland during surgery. It presents with sudden headache, visual disturbances, and potential acute hypopituitarism, which could explain some of the patient's symptoms.
• Cerebral Vasospasm: This is a potentially life-threatening complication that can occur after subarachnoid hemorrhage or neurosurgical procedures. While the patient's symptoms do not directly suggest vasospasm, the recent surgery and presence of headache warrant consideration of this diagnosis.

Rare Diagnoses

• Thyroid Storm or Crisis: Although less likely, thyroid dysfunction could explain some of the patient's symptoms, such as weight loss and potentially the hyponatremia. However, this would be unusual in the context provided without other specific symptoms of thyroid disease.
• Pseudohyponatremia: This condition, often associated with hyperlipidemia or hyperproteinemia, could artificially lower serum sodium measurements. However, given the clinical context, this seems less likely to be the primary issue.