Medicine>>>>>Nephrology
Question 1#

A 76-year-old man presents to the emergency room. He had influenza and now presents with diffuse muscle pain and weakness. His past medical history is remarkable for osteoarthritis for which he takes ibuprofen, and hypercholesterolemia for which he takes lovastatin. Physical examination reveals blood pressure of 130/90 with no orthostatic change. The only other finding is diffuse muscle tenderness. Laboratory data include 

• BUN: 30 mg/dL
• Creatinine: 6 mg/dL
• K: 6.0 mEq/L
• Uric acid: 18 mg/dL
• Ca: 6.5 mg/dL
• PO4 : 7.5 mg/dL
• UA: large blood, 2+ protein. Microscopic study shows muddy brown casts and 0 to 2 rbc/hpf (red blood cells/high power field). 

Which of the following is the most likely diagnosis?

A. Nonsteroidal anti-inflammatory drug-induced acute kidney injury (AKI)
B. Volume depletion
C. Rhabdomyolysis-induced acute kidney injury
D. Urinary tract obstruction
E. Hypertensive nephrosclerosis

Correct Answer is C

Comment:

Rhabdomyolysis-induced AKI is characterized by hyperkalemia, hyperphosphatemia, and hyperuricemia, all caused by release of intracellular muscle products. The high phosphorus level causes hypocalcemia. The BUN/creatinine ratio, normally 10/1, is reduced because of release of muscle creatine, which is converted to creatinine. The load of creatinine to be excreted by the failing kidney therefore exceeds the urea load, which is little changed. The presence of “blood” on the dipstick determination is caused by myoglobinuria. The dipstick registers red blood cells, hemoglobin (eg, from intravascular hemolysis), and myoglobin as “blood.” Trauma, medications (especially statins), infectious processes (influenza, sepsis), and extreme muscular exertion (seizures, exertional heat stroke) are common causes.

All nonsteroidal agents may cause decreased renal function. Usually this is attributed to decreased blood flow—less commonly, to drug-induced interstitial nephritis. The laboratory abnormalities in this case do not suggest decreased blood flow or interstitial nephritis. However, stopping the ibuprofen would be prudent. The absence of orthostatic hypotension makes the diagnosis of volume depletion very unlikely. Nothing on history, physical examination, or electrolyte abnormalities suggests obstruction. However, in a 76-year-old man, a renal sonogram to rule out occult obstruction would be reasonable. Hypertensive nephrosclerosis causes chronic rather than acute renal insufficiency and would not account for the electrolyte abnormalities.