Differential Diagnosis

The patient's laboratory results, including a DST (dexamethasone suppression test) of 289, ACTH (adrenocorticotropic hormone) <5, and am cortisol 0.6, suggest an abnormality in the hypothalamic-pituitary-adrenal (HPA) axis. Here's a differential diagnosis based on the provided categories:

• Single Most Likely Diagnosis
  • Primary Adrenal Insufficiency: The low morning cortisol level (am cortisol 0.6) and low ACTH (<5) suggest a primary issue with the adrenal glands, as the adrenal glands are not producing enough cortisol, and the pituitary gland is not producing enough ACTH to stimulate them. This could be due to Addison's disease or another cause of adrenal gland failure.
• Other Likely Diagnoses
  • Secondary Adrenal Insufficiency: Although less likely given the very low ACTH, this condition occurs when the pituitary gland does not produce enough ACTH, leading to decreased cortisol production by the adrenal glands. The DST result might not fully support this, but it's worth considering if there are other clinical indicators.
  • Adrenal Crisis: Given the very low cortisol level, the patient could be in or at risk for an adrenal crisis, a life-threatening condition that requires immediate treatment.
• Do Not Miss Diagnoses
  • Pituitary Apoplexy: A condition where the pituitary gland suddenly hemorrhages or becomes infarcted, leading to acute secondary adrenal insufficiency among other hormonal deficiencies. It's a medical emergency.
  • Sheehan Syndrome: Postpartum necrosis of the pituitary gland, leading to hypopituitarism, which could include adrenal insufficiency.
• Rare Diagnoses
  • Familial Glucocorticoid Deficiency: A rare genetic disorder affecting the adrenal glands' ability to produce cortisol.
  • Triple A Syndrome (Allgrove Syndrome): A rare autosomal recessive disorder characterized by adrenal insufficiency, alacrima (absence of tear secretion), and achalasia (swallowing difficulty).

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory results, and potentially additional testing for confirmation. The very low cortisol and ACTH levels, in particular, point towards a significant issue with the adrenal glands or the pituitary gland's ability to stimulate them.