Case 1: Diagnostic Testing

Case 1 Index

Click to reveal some blood test!
Initial results
Choose the four most high yield diagnostic test to perform next!
PET scan
PET scans can be very helpful to locate inflammation and are most often used to look for areas of abnormal increased metabolic activity in patients with certain cancers. However, in this patient, our history and physical exam already showed us that he is inflamed with precise localization to several joints. Try again!
Correct! This the most important diagnostic test to perform as we want to rule out the most dangerous disease on our differential diagnosis – septic arthritis. A newly inflamed joint should always be aspirated, if possible. We want to see the cell count (especially white blood cells), send fluid for gram stain and culture, and perform a crystal exam. The most accessible joint to aspirate in this patient is, likely, one of his knees. Below is a quick reminder of how to interpret the synovial fluid cell count:
Plan films of affected joints
Correct! X-ray can be very helpful in determining whether there is chronic damage to the joint and the pattern of damage can clue us in to the etiology of joint swelling.
Rheumatoid factor and anti-cyclic citrullinated peptide antibody (anti-CCP)
Correct! When evaluating polyarticular joint swelling, it behooves us to consider rheumatoid arthritis. Classically, RA is thought of as a symmetric disease with a predilection to PIPs and MCPs, it but can affect many other joints (least likely being vertebral column, with the exception of atlantoaxial joint). Keep in mind that peak incidence of RA is in the 6th decade.
Uric acid level
Correct! We suspect this patient may have polyarticular gout and uric acid level above 7 will help support our diagnosis and guide treatment. Note that normal uric acid level would not rule out an acute gout flare and an arthrocentesis needs to be performed to exclude infection and confirm the presence of crystals.
Incorrect. Although joint involvement may occur in ANA+ disease, such as lupus, this patient’s presentation is not consistent with lupus and ANA is too non-specific of a marker to be helpful. 
Venous duplex ultrasound of lower extremities
Incorrect. While deep venous thrombosis is certainly on the differential diagnosis for a swollen extremity, this patient has multiple swollen joints, which cannot be explained by a DVT. Let’s try again!

Click here to move on!

Case 1 Index
Case 1 Introduction
Case 1 Review of Systems

Case 1 Physical Exam