Differential Diagnosis

The patient's symptoms of worsening swelling in her lower extremities, occasional dizziness, headache, and significantly low blood pressure (90/60 mm Hg) suggest an adverse effect from her recently started antihypertensive medication. Here's a categorized differential diagnosis:

• Single most likely diagnosis:

  • Lisinopril: This is an ACE inhibitor, which can cause a significant drop in blood pressure, especially after initiation or dose increase. The patient's symptoms of dizziness and low blood pressure are consistent with this effect. Additionally, ACE inhibitors can cause increased bradykinin levels, leading to increased vascular permeability and potentially worsening edema.

• Other Likely diagnoses:

  • Metoprolol: A beta-blocker that can also lower blood pressure. While it's less likely to cause such a pronounced drop as seen with ACE inhibitors, especially in the context of edema, it could contribute to hypotension, particularly if the patient is sensitive to its effects or if there's an interaction with other medications.
  • Amlodipine: A calcium channel blocker that can cause peripheral edema as a side effect. However, it's less likely to cause significant hypotension compared to ACE inhibitors, especially in the absence of other symptoms like reflex tachycardia.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):

  • Chlorthalidone-induced hypovolemia: Although less likely given the context of edema, chlorthalidone is a diuretic that can lead to hypovolemia and subsequent hypotension if not balanced with adequate fluid intake. This would be particularly concerning if the patient has been experiencing increased urine output without adequate fluid replacement.
  • Renal failure: Both ACE inhibitors (like Lisinopril) and diuretics (like Chlorthalidone) can affect renal function, especially in patients with pre-existing renal issues. A significant drop in blood pressure can also reduce renal perfusion, potentially exacerbating or revealing underlying renal dysfunction.

• Rare diagnoses:

  • Vasovagal reaction: Although rare and less directly related to the medications listed, a vasovagal reaction could potentially cause hypotension and some of the symptoms described. However, this would typically be associated with a more acute onset and possibly other symptoms like nausea or syncope.
  • Medication interaction: If the patient is taking other medications not listed here, there could be an interaction that's contributing to her symptoms. This would be rare and dependent on the specific medications involved but is always a consideration in patients on multiple drugs.