Your arthrocentesis results are back:
Gram stain – negative
Culture – no growth
Cell count – 46,170 WBC with 100% neutrophils
Now it’s time to look under the microscope, by clicking below:
What do you see under the polarized microscope?
Positively birefringent crystals
Positive birefringence means that crystals appear blue when aligned parallel with the slow axis of the red compensator. Positively birefringent rhomboid crystals are associated with pseudogout or calcium pyrophosphate deposition disease. The crystals we are seeing under the microscope for Mr. S are different. Try again!
Negatively birefringent crystals
Correct! The needle-shaped yellow crystals we see under the microscope are negatively birefringent. Think about with which condition this finding is classically associated.
RF < 20
Anti-CCP = 0
Serum uric acid = 9.0
Click below to view the Xray, think about how you would describe and then reveal the radiologist’s read!
Left knee X-Ray
There is a ill-defined juxta-articular erosion of the lateral distal femur. Cortical irregularity of the medial proximal tibia may also represent an erosion. No soft tissue calcification identified.
Click here to reveal the final diagnosis and teaching points!