What is the significance of the tests ordered in making the diagnosis of CPPD?
First ever validated classification criteria for symptomatic CPPD disease was developed in 2023 by American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR).  In contrast to previous unvalidated criteria proposed by Ryan and McCarty, research laboratory techniques that are not widely available (e.g. x-ray diffraction, Fourier transform infrared  [FTIR]) are excluded from the items of the new 2023 ACR/EULAR criteria. 

2023 ACR/EULAR classification criteria: 
1. Entry criterion: Ever had at least one episode of joint pain, swelling, or tenderness.+ 
2. Absolute exclusion criteria: All symptoms are more likely explained by an alternate condition (such as rheumatoid arthritis, gout, psoriatic arthritis, osteoarthritis, etc.) 
3. Sufficient criteria: 1. Crowned dens syndrome* or 2. Synovial fluid analysis demonstrating CPP crystals in a joint with swelling, tenderness or pain.**
An individual is classified as CPPD if the entry criterion is met, exclusion criteria are not met, and at least one sufficient criterion is fulfilled. If none of the sufficient criteria are present, an individual is classified as CPPD disease if the sum of the criteria below is >56 points. (see table 2)

In the 2023 ACR/EULAR classification criteria, several diagnostic tools should be included as followings
1. Joint effusion analysis 
   -Under polarizing light microscope, CPP crystal appears rhomboid-shaped with triclinic structures and positive birefringent. When the long axis of the crystal was parallel to the Z axis (parallel to the axis of the compensator), the color of the crystal was blue. When the long axis of the crystal was parallel to the X axis (perpendicular to the axis of the compensator), the color of the crystal was yellow. (see Reference)
2. Image modalites 
    -Xray
    -Ultrasound (US)
    -Computed tomography (CT)
    -Dual-energy computed tomography (DECT)

What are the typical features seen in this patient that are helpful in making the diagnosis of CPPD disease?

1. CPPD disease is clearly a disease of aging and is rare in patients younger than 60 years of age. Previous trauma to the joint is also a strong risk factor for CPPD. It presented with acute or chronic form as follow.

• (A). Acute CPP crystal arthritis (or pseudogout) is the most widely recognized form of CPPD disease. Patients typically present with the acute onset of monoarticular (n=1) or oligoarticular (n=2-4) arthritis. The knee is the most commonly involved joint (over 50 percent), followed by the wrist; Other joints typically affected in acute CPP crystal arthritis include wrists, shoulders, ankles, feet, and elbows. Acute podagra in the first metatarsophalangeal joint is rare. Systemic symptoms including fevers, chills, and constitutional symptoms often occur with acute CPP crystal arthritis. In contrast to the brief attacks of acute gouty arthritis that typically last for several days to 1 week, acute attacks of CPPD disease may last for weeks to months. An upper extremity site of inflammation (wrist, elbow, shoulder) for a first attack should raise suspicion for acute CPP crystal arthritis.
• (B). Chronic CPP crystal arthritis comprises several clinical phenotypes, including osteoarthritis-like arthritis and rheumatoid arthritis-like (often called pseudo-rheumatoid arthritis). Most affected patients have a polyarticular (n>4) form of arthritis. Osteoarthritis-like arthritis is usually distinguishable from typical osteoarthritis by flares of inflammatory signs and symptoms and by unusually severe articular damage. The involvement of joints such as the glenohumeral joint, the wrist, and the metacarpophalangeal joints, which are not often affected by typical osteoarthritis, should lead one to suspect the presence of CPPD disease.Rheumatoid arthritis-like chronic CPP crystal arthritis presented with persistent inflammatory arthritis that affects large and small joints. Flares in this phenotypic variant of CPPD disease often involve joints sequentially, and involvement is less symmetric than that seen with rheumatoid arthritis. Articular inflammation may last up to several months, and inflammation in affected joints tends to wax and wane independently of one another, in distinction to RA, where synchronous flare and remission are more typical. (see NEJM, uptodate).

What are the next steps in management of this patient? 
Acute CPP crystal arthritis is managed with strategies that are aimed at reducing inflammation and that are borrowed from therapies used for acute gouty arthritis. Effective therapy included colchicine, NSAID, systemic glucocorticoids or intrarticular injection of glucocorticoids. Chronic CPP crystal arthritis is much more difficult to manage than acute CPP crystal arthritis. Few controlled trials of any therapies exist, and all the current therapeutic strategies are also aimed at reducing inflammation (see Proposed treatment algorithm).

ACGME Core Competency
Patient Care (Case Correlation to ACGME Core Competency Requirements)
1.Understand the most important test for diagnosis of CPPD disease.
2.Recognize the clinical manifestations of CPPD disease.
3.Obtain an appropriate history to determine if a patient presented with joint swelling.
4.Determine what is the initial step encountering similar patient and when to refer to rheumatology.

Medical Knowledge (Case Correlation to ACGME Core Competency Requirements)
1.Understand the evaluation of joint pain and swelling.
2.Understand the imaging abnormality of joint including xray and ultrasound.
2.Interpret the results of synovial fluid analysis.
3.Determine how to treat patient with CPPD disease.

Practice-Based Learning and Improvement (Case Correlation to ACGME Core Competency Requirements)
1.Set goals for studying about CPPD disease epidemiology, risk factor, clinical manifestations, diagnosis and treatment options.
2.Demonstrate the ability to perform arthrocentesis.

Practice-Based Learning and Improvement (Case Correlation to ACGME Core Competency Requirements)
1.Set goals for studying about AOSD pathophysiology, clinical manifestations, and treatment options.
2.Demonstrate the ability to review and interpret literature relevant to the care of patients with AOSD.

Interpersonal and Communication Skills (Case Correlation to ACGME Core Competency Requirements)
1.Discuss the results of lab and radiographic finding with a patient.
2.Discuss the diagnosis of CPPD disease with a patient.
3.Discuss the need for appropriate follow up and monitoring with a patient
4.Comprehensively explain different treatment options based on disease manifestations.

Professionalism (Case Correlation to ACGME Core Competency Requirements)
1.Encourage patients and family to ask questions regarding their disease and empower them to be active participants in their care.
2.Provide adequate time and accessibility to address patient and family’s concerns.
3.Demonstrate an understanding of informed consent with regard to invasive procedure like arthrocentesis.

System-Based Practice (Case Correlation to ACGME Core Competency Requirements)
1.Create a team approach to manage patients with arthritis and fever of unknown cause, engaging physicians from multiple disciplines.
2.Identify barriers to access and delivery of care for patients with recurrent , refractory diseases.
3.Learn about resources available to improve delivery of care and patient support.