Repeated USMLE Questions Step 1- 233

A 56- year old man presents to the clinic due to recurrent attacks of severe pain in his right big toe for the last few weeks. During the attacks, his toe becomes painful, red, warm and swollen. Significant improvement occurs after treatment with colchicine. Synovial fluid analysis is performed to confirm the diagnosis.

What is the most likely finding to confirm the diagnosis?

A- Calcium oxalate crystals

B- Calcium pyrophosphate dehydrate crystals

C- Cholesterol crystals

D- Cloudy, reddish fluid, with leucocytes’ count equal to the blood count

E- Negatively birefringent urate crystals

Answer






This is a case of gout supported by the patient complaint of recurrent inflammation of the big toe and improvement of symptoms after the use of colchicine. Acute gout is confirmed by the detection of negatively birefringent monosodium urate crystals in synovial fluid analysis. Calcium pyrophosphate dehydrate crystals are found in cases of pseudo-gout. Acute arthritis is characterized by cloudy, bloody synovial fluid with leucocytes count equal to the blood count (normally synovial fluid may contain up to 200 cells /UL white blood cells). Cholesterol crystals are seen in patients with hypercholesterolemia and rheumatoid arthritis while calcium oxalate crystals can be seen in patient with renal diseases on dialysis.

The correct answer is E

Repeated USMLE Questions Step 1- 222

A 23 year-old woman was involved in a motor car accident three days ago. She was hypotensive and diagnosed with internal bleeding. She received several units of blood. Today her urine output is very low for the last six hours.  Her urinalysis showed hematuria, proteinuria, muddy brown epithelial cells and granular casts. Her lab tests also show BUN: 26 mg/dL and serum creatinine: 2.6 mg/dL.

What is the most likely diagnosis of her renal pathology?

A-Acute glomerulonephritis

B-Interstitial nephritis

C-Acute tubular necrosis

D-Traumatic avulsion of the ureter

Answer






Acute tubular necrosis (ATN) is the most likely pathology in this case. It is caused by decrease in blood volume which leads to prerenal azotemia. The most common cause of renal failure associated with prerenal azotemia is acute tubular necrosis. It is characterized by rapid decline of renal function and acute elevation of blood urea and serum creatinine. The BUN/creatinine ratio is usually normal as in this case. The muddy brown epithelial cells and granular casts are also typical in ATN. Acute glomerulonephritis is characterized by the humpy lumpy appearance under light microscope and sub epithelial humps under electron microscope. It is type III hypersensitivity forming immune complexes (antigen-antibody complexes) which deposit below the podocyte foot processes of the basement membrane of the glomeruli. It occurs mainly after streptococcal infection. Interstitial nephritis is inflammation of the kidney tissue that surrounds the tubules. It is caused mainly as a side effect of some drugs or post-infection. It is characterized by eosinophilia and eosinophiluria. Traumatic avulsion of the ureter is mainly occurs as a complication of ureteroscopy. There is no mention to any surgery or trauma of any kind in this patient’s history.

The correct answer is C