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  #1  
Old 09-07-2012
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Default Which arthritis?

A 40 yr old man presents to ER with excruciating knee joint pain of sudden onset. Synovial fluid aspirate show crystals. When examined with a polarizing filter, they appear blue when aligned perpendicular to the slow axis of the red compensator.
What is the most likely diagnosis:
A. Gout
B. Pseudogout
C. Septic arthritis
D. Osteoarthritis
E. Rheumatoid Arthritis
F. SLE

Please answer with an explanation.
Thanks

Last edited by Novobiocin; 09-07-2012 at 08:03 AM.
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  #2  
Old 09-07-2012
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ans A .........
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Old 09-07-2012
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Quote:
Originally Posted by Novobiocin View Post
A 40 yr old man presents to ER with excruciating knee joint pain of sudden onset. Synovial fluid aspirate show crystals. When examined with a polarizing filter, they appear blue when aligned perpendicular to the slow axis of the red compensator.
What is the most likely diagnosis:
A. Gout
B. Pseudogout
C. Septic arthritis
D. Osteoarthritis
E. Rheumatoid Arthritis
F. SLE

Please answer with an explanation.
Thanks
A.) Gout: with parallel light: yellow
perpendicular light: blue
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  #4  
Old 09-07-2012
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Answer B


Quote:
Uniaxial birefringent materials are classified as positively (or negatively) birefringent when, for light (having parallel and perpendicular components) directed to the optic axis, the refractive index of light polarized parallel to the optic axis is greater (or smaller, respectively) than light polarized perpendicularly to the optic axis.[6] In other words, the polarization of the slow (or fast) wave is parallel to the optical axis when the birefringence of the crystal is positive (or negative, respectively).
I couldnt understand the above diagram and theory ,I pasted because maybe somebody could.The bottom quote explains the answer
Quote:
Needle aspiration of fluid from a gouty joint will reveal negatively birefringent monosodium urate crystals. Calcium pyrophosphate crystals, in contrast, show weak positive birefringence. In practice, urate crystals appear yellow and calcium pyrophosphate crystals appear blue when their long axes are aligned parallel to that of a red compensator filter,or a crystal of known birefringence is added to the sample for comparison.
The refraction perhaps (not sure) has something to do with VIBGYOR Violet, Indigo,Blue,Green, Yellow,Orange and Red

Source http://en.wikipedia.org/wiki/Birefringence
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Old 09-07-2012
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A is the answer......had to memorize this many a times during my step 1 prep
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  #6  
Old 09-07-2012
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B
just memorize that BLUE WHEN PERPENDICULAR = PSEUDOGOUT

YELLOW when perpendicular = GOUT

They are essentially the opposite
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Quote:
Originally Posted by XpaezX View Post
B
just memorize that BLUE WHEN PERPENDICULAR = PSEUDOGOUT

YELLOW when perpendicular = GOUT

They are essentially the opposite
Gotcha!

You fell right into the trap
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Old 09-07-2012
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well this qs is confusing me coz

knee is affected so its pseudogout , gout would affect toe

but gout has crystals blue when perpendicular ....... so if we go by this it should be A
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Old 09-07-2012
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Quote:
Originally Posted by Hitman View Post
well this qs is confusing me coz

knee is affected so its pseudogout , gout would affect toe

but gout has crystals blue when perpendicular ....... so if we go by this it should be A
That's the whole point of this exercise. :sorry:
You have to know 100% which finding/investigation is pathognomic/diagnostic for a a particular condition.
Trust your knowledge.
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  #10  
Old 09-07-2012
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So the correct answer is A ?
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Quote:
Originally Posted by step_enhancer View Post
So the correct answer is A ?
Yes.
This question is not from any Q Bank. I wrote it myself to highlight the fact that in the real exam they might not spoonfeed us by giving typical scenarios like "toe" for gout (It can affect knee too) and negative birefringence in gout (yellow with parallel light) but blue with perpendicular light means the same thing (negative birefringence) if you know the concept well.
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  #12  
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@novobiocin........well done sir.....nice work.....!!!
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Quote:
Originally Posted by Novobiocin View Post
Yes.
This question is not from any Q Bank. I wrote it myself to highlight the fact that in the real exam they might not spoonfeed us by giving typical scenarios like "toe" for gout (It can affect knee too) and negative birefringence in gout (yellow with parallel light) but blue with perpendicular light means the same thing (negative birefringence) if you know the concept well.
Awesome ........Thanks

Totally agree with you .
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