Question of the Week # 44

A 24 y/o athlete presents to your office with complaints of reddish discoloration of urine. He claims that he has been exercising and running vigorously for the past two days. He is very determined to lose the extra weight that he has put up in the recent months and has been fasting in the nights for the past one week. His past medical history is significant for two abdominal surgeries which included laparotomy and appendicectomy in the past for intermittent severe abdominal pain. The patient does not smoke but does occassional consumes alcohol in binges. He did involve in one such alcohol binge last night. Physical examination is benign except for decreased power and reflexes in bilateral lower extremities. There is no rash. His urine specimen was grossly red in color. Urine dipstick was negative for protein, blood, leucoesterase and nitrite. Urine microscopy did not reveal any RBCs, WBCs or Casts. Serum creatinine and complete blood count are with in normal limits. A Creatinine Phosphokinase ( CPK) level has been ordered but is not yet available. The most likely cause of this patient’s grossly red urine is :

A) Rhabdomyolysis
B) Paroxysmal Nocturnal Hemoglobinuria
C) Acute Intermittent Porphyria
D) Await CPK level for correct diagnosis
E) Glomerulonephritis

9 Responses

  1. c

  2. c

  3. a

    • ans
      ; c

  4. Ans.C

    Reddish discolration of urine with a negative dipstick for blood suggests that this red color is not from either a pigment globin ( hemoglobin or myoglobin) or a Red blood cell ( Hematuria). Such red colored urine with negative dipstick can be seen with drugs such as Rifampin, foods such as beets and substances like porpyrins in urine.

    This patient also has sensory as well as motor neuropathy in his lower extremities, a typical manifestation of Acute intermittent porpyria attacks. The presence of peripheral neuropathy in patients with history of recurrent abdominal pains should raise the suspicion of Acute Intermittent Porphyria ( AIP). This patient had several severe abdominal pain episodes which were misdaiagnosed as appendicitis and he even underwent a futile laparotomy. Patients are pain free between the attacks. Fasting and drugs like phenobarbital, alcohol can precipitate AIP attacks. Unlike other porphyrias, rash is not typically seen in AIP.

    A. is not the answer because dipstick would be positive for blood in rhabdomyolyisis.

    B. is not the answer because dipstick would be positive in hemoglobinuria.

    D. is not the answer since the diagnosis of reddish urine here is not in favor of myoglobinuria.

    E. a negative dipstick and negative microscopic urinalysis rules out gross hematuria as a cause of this red urine.

    F. Negative dipstick for blood, negative urine microscopy and absence of RBC casts rule out glomerulonephritis as a cause of this patient’s red urine.

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  5. C

  6. good onr

  7. The neg blood in the urine rules out rhabdo and pnh and GN.CPK is pending so it not significant since they want you to answer the question w/o the lab.But its not an emergency so u can wait for results.You can give fluids while you wait…thats obvious.
    The only one left is AIP. Its a little confusing with all the Sx. I wonder if the USMLE always tries to give red herrings to trick u. Its not real life but we have no choiuce

  8. C

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