An 82-year-old patient presents with nausea and weakness. She has a 3-year history of type 2 diabetes mellitus, as well as essential hypertension and congestive heart failure. Her medications include insulin glargine, hydrochlorothiazide, lisinopril, metoprolol, and digoxin. Medication doses have not recently been changed. Physical examination reveals clear lung fields, regular heart rhythm at 56 beats/minute, a soft systolic murmur that radiates to the axilla, and normal liver size. There is no peripheral edema or jugular venous distension. Chest x-ray shows cardiomegaly without pulmonary vascular congestion. Her CBC is normal. Multichannel chemistry profile shows potassium of 4.0 mEq/L and serum creatinine of 1.2 mg/dL (normal range 0.5-1.3). Digoxin level is 2.2 (therapeutic 0.8-1.5).
What condition is most likely to account for her symptoms?
A. Decreased glomerular filtration rateIn the usual patient, glomerular filtration rate drops by about 1 mL/minute every year after the age of 60. However, muscle mass and therefore creatinine production and excretion decline proportionately. Therefore, the serum creatinine can remain within the normal range despite considerable renal dysfunction. This can lead to the accumulation of drugs that are cleared by renal mechanisms. This problem can be avoided if an “estimation formula” (ie, the Cockcroft-Gault or the MDRD equation) is used; they provide an accurate estimation of GFR, similar to a 24-hour urine collection for creatinine clearance. Although polypharmacy is a common cause of gastrointestinal side effects in the elderly, this patient has been on a stable regimen; of her medications, only digoxin is likely to cause nausea or vomiting. Congestive heart failure can cause nausea by causing passive congestion of the liver, but this patient’s heart failure appears clinically well compensated. In particular, she does not have tender hepatomegaly or hepatojugular reflux. The combination of an ACE inhibitor and beta-blocker is often very effective in preserving myocardial function. Diabetic gastroparesis can cause nausea and vomiting but rarely occurs after such a short history of diabetes. Lung capacity (including forced vital capacity and lung elastic recoil) often deteriorates with the aging process and can cause dyspnea and fatigue even in the nonsmoker, but would not cause her gastrointestinal symptoms.