Differential Diagnosis for SIADH
The Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is characterized by the excessive release of antidiuretic hormone (ADH) from the posterior pituitary gland or another source, leading to water retention and resulting in hyponatremia. The differential diagnosis for SIADH can be categorized as follows:
- Single Most Likely Diagnosis + Small Cell Lung Cancer: This is a common cause of SIADH due to the ectopic production of ADH by tumor cells. The presence of hyponatremia in a patient with small cell lung cancer should prompt consideration of SIADH.
- Other Likely Diagnoses + Pulmonary Infections: Conditions such as pneumonia, tuberculosis, and abscesses can lead to SIADH, possibly due to the inflammatory response affecting ADH regulation. + Central Nervous System Disorders: Conditions affecting the CNS, such as stroke, hemorrhage, and traumatic brain injury, can disrupt normal ADH secretion, leading to SIADH. + Drugs: Various medications, including certain antidepressants (SSRIs), antipsychotics, and antiemetics, are known to cause SIADH as a side effect.
- Do Not Miss Diagnoses + Myxedema (Hypothyroidism): Although less common, hypothyroidism can cause SIADH-like symptoms due to decreased cardiac output and increased ADH secretion. Missing this diagnosis could lead to inappropriate treatment and worsening of the patient's condition. + Adrenal Insufficiency: This condition can mimic SIADH due to the decreased production of cortisol, which affects water and electrolyte balance. Failure to diagnose adrenal insufficiency can be life-threatening.
- Rare Diagnoses + Lymphoma: Certain types of lymphoma can cause SIADH, either through direct production of ADH or through the effects of cytokines on ADH regulation. + Thyroid Disorders (Other Than Myxedema): Rarely, other thyroid disorders, such as thyroiditis or hyperthyroidism, can lead to SIADH, possibly through mechanisms involving ADH regulation and fluid balance. + Guillain-Barré Syndrome: This autoimmune disorder can affect the autonomic nervous system, potentially leading to SIADH. It is a rare but important consideration in the differential diagnosis.