An 80-year-old woman is brought to the emergency department from a nursing home due to progressive lethargy. The patient has a history of Alzheimer disease and at baseline is conversant and able to indicate her needs. For the past several days, she has been somnolent and lying in bed most of the time. She has had no fever, vomiting, or diarrhea. Two weeks ago, the patient was treated with ciprofloxacin for a urinary tract infection. Her other medical problems include hypertension, type 2 diabetes mellitus, and coronary artery disease. Blood pressure is 100/60 mm Hg, pulse is 100/min, and respirations are 20/min. Mucous membranes are dry. Lungs are clear to auscultation, and heart sounds are normal. The abdomen is soft and nontender. The patient has no skin rash. Laboratory results are as follows: A month ago, her serum creatinine was 0.9 mg/dL. Which of the following is the most likely cause of this patient's current renal abnormality?

Question

An 80-year-old woman is brought to the emergency department from a nursing home due to progressive lethargy.  The patient has a history of Alzheimer disease and at baseline is conversant and able to indicate her needs.  For the past several days, she has been somnolent and lying in bed most of the time.  She has had no fever, vomiting, or diarrhea.  Two weeks ago, the patient was treated with ciprofloxacin for a urinary tract infection.  Her other medical problems include hypertension, type 2 diabetes mellitus, and coronary artery disease.  Blood pressure is 100/60 mm Hg, pulse is 100/min, and respirations are 20/min.  Mucous membranes are dry.  Lungs are clear to auscultation, and heart sounds are normal.  The abdomen is soft and nontender.  The patient has no skin rash.  Laboratory results are as follows:  A month ago, her serum creatinine was 0.9 mg/dL.  Which of the following is the most likely cause of this patient's current renal abnormality?

Quizplus · Accepted Answer

11ec25c8_d112_801a_bc81_61abcec3a713_MD0003_00 This patient with tachycardia, mild hypotension, and dry mucous membranes most likely has intravascular volume depletion leading to prerenal acute kidney injury (AKI). Elderly patients can be especially susceptible to volume depletion due to an impaired thirst response and often an inability to obtain food and water without assistance (eg, due to dementia). Hypovolemia leads to decreased renal blood flow and causes activation of the renin-angiotensin-aldosterone system. Increased resorption of salt and water occurs, leading to an increase in the passive resorption of urea and resulting in an elevated blood urea nitrogen/creatinine ratio >20:1. The term "injury" is somewhat inaccurate in the prerenal state as the kidneys do not experience actual injury unless decreased renal perfusion is prolonged (leading to acute tubular necrosis). Therefore, an unremarkable urinalysis (absence of significant protein, cells, or casts) is typical. renin-angiotensin-aldosterone system (Choice A) Age-related decline in renal function occurs due to loss of renal mass and thickening of the glomerular basement membrane. However, the process is gradual and cannot account for this patient's relatively abrupt decrease in renal function. (Choice B) Atherosclerotic renovascular disease leads to renal artery stenosis. Significant bilateral disease is required to result in serum creatinine elevation and typically presents with hypertension rather than hypotension. (Choice C) Drug hypersensitivity reaction can cause intrinsic AKI due to acute interstitial nephritis (AIN). Ciprofloxacin can cause AIN; however, absence of leukocyte casts on urinalysis and no skin rash make AIN unlikely. (Choice D) Increased central venous pressure occurs in volume overload due to heart failure, which can cause prerenal AKI due to impaired forward blood flow. However, dry mucous membranes make volume overload unlikely. (Choice F) Nodular glomerulosclerosis occurs in diabetic nephropathy; renal dysfunction typically develops gradually (rather than over 1 month), and significant proteinuria is expected. (Choice G) Obstructive uropathy (postrenal AKI) is generally uncommon in women as benign prostatic hyperplasia is the most common cause. (Choice H) Suppression of antidiuretic hormone occurs in the setting of low blood osmolality. However, antidiuretic hormone release will be stimulated in this patient due to nonosmotic stimulation from hypovolemia. nonosmotic stimulation (Choice I) Aminoglycosides (eg, gentamicin) can cause intrinsic AKI due to renal tubular toxicity; however, ciprofloxacin is not associated with direct renal tubular damage. Educational objective: The elderly can be especially susceptible to intravascular volume depletion leading to prerenal acute kidney injury. There is often a history of poor oral intake or excessive volume loss (eg, diarrhea). Laboratory results typically demonstrate a blood urea nitrogen/creatinine ratio >20:1 and an unremarkable urine sediment. References: Management of acute renal failure in the elderly patient: a clinician's guide. (http://www.ncbi.nlm.nih.gov/pubmed/18540687)

An 80-Year-Old Woman Is Brought to the Emergency Department from a Nursing