CPPD Classification Calculator (2023 ACR/EULAR)

Entry Criterion Must be met before any other criteria apply

At least one episode of joint pain, swelling, or tenderness?

Occurring in a peripheral joint or, in the case of crowned dens syndrome, an axial joint such as C1/C2. This is required to proceed with any further classification.

Are ALL symptoms more likely explained by an alternative condition?

Examples include rheumatoid arthritis, gout, psoriatic arthritis, osteoarthritis, etc. If another condition fully explains all symptoms, CPPD classification does not apply. Patients may still be assessed if only some symptoms could be due to CPPD.

Crowned dens syndrome (CDS) confirmed, OR CPP crystals in synovial fluid?

Crowned dens syndrome requires both: (a) clinical features (acute/subacute severe upper neck pain, elevated inflammation markers, limited rotation, often fever - with polymyalgia rheumatica and meningitis excluded) AND (b) imaging features (CT showing linear calcific deposits in the transverse retro-odontoid ligament, or DECT with dual-energy index 0.016-0.036).

CPP crystals in synovial fluid from a joint with swelling, tenderness, or pain. Note: CPP crystals in cartilage in end-stage OA when all symptoms are explained by OA does not qualify.

Clinical

Age at Onset of Joint Symptoms

0 / 4 pts

Age when joint pain, swelling, or tenderness first began. CPPD is strongly associated with older age; onset after 60 is a key positive feature.

Age ≤60 years at onset

Age >60 years at onset

Time-Course and Symptoms of Inflammatory Arthritis

0 / 16 pts

A typical episode is defined as an episode with acute onset or acute worsening of joint pain with swelling and/or warmth that resolves regardless of treatment. Persistent inflammatory arthritis means ongoing joint swelling with pain and/or warmth in one or more joints. Select the highest-weighted item that applies.

More than one typical acute arthritis episode Recurrent episodes of acute onset/worsening of joint pain with swelling/warmth that resolve irrespective of treatment

+16

One typical acute arthritis episode Single episode with acute onset/worsening of joint pain with swelling/warmth that resolved irrespective of treatment

+12

Persistent inflammatory arthritis Ongoing joint swelling with pain and/or warmth in one or more joints (not episodic)

No persistent or typical inflammatory arthritis

Sites of Typical Episode(s) - Peripheral Joints

0 pts

Location of inflammatory episode(s) in peripheral joints. The knee and wrist are the most characteristic sites for CPPD. First MTP involvement is atypical for CPPD (it suggests gout) and is scored negatively. Select only the highest-weighted item that applies.

KneeKnee joint involvement during typical episode(s)

WristWrist joint involvement during typical episode(s)

Joint(s) other than wrist, knee, or 1st MTPShoulder, elbow, ankle, hip, or other peripheral joints

No typical episode(s)

1st Metatarsophalangeal Joint (1st MTP) Involvement of the big toe MTP joint - atypical for CPPD, more characteristic of gout

-6

Related Metabolic Diseases

0 / 6 pts

Specific metabolic conditions that predispose to CPP crystal deposition through various mechanisms. These include hereditary hemochromatosis, primary hyperparathyroidism, hypomagnesemia, Gitelman syndrome, hypophosphatasia, or a familial history of CPPD disease (first-degree relative).

Related metabolic disease presentAny of the above conditions confirmed

None / not present

Laboratory

Synovial Fluid Crystal Analysis

0 pts

From a symptomatic joint or bursa. Should be performed by a trained observer using compensated polarized light microscopy. CPP crystals have positive birefringence and may be weakly or non-birefringent - regular light microscopy may be more sensitive. If not performed, score as 0.

Not performed

CPP crystals absent on 1 occasion Single negative synovial fluid analysis from a symptomatic joint

-1

CPP crystals absent on ≥2 occasions Two or more negative analyses from symptomatic joint(s)

-7

Imaging

Imaging requirement: When sufficient criteria are not met, imaging of at least one symptomatic peripheral joint by CR (X-ray), ultrasound, CT, or DECT is required to be considered for classification. Items can only be scored if imaging has been performed.

OA of Hand / Wrist on Imaging

0 / 7 pts

Osteoarthritis at specific hand/wrist joints on imaging (K/L score ≥2). These particular joint patterns are characteristic of CPPD-associated OA. Score the highest-weighted finding.

≥2 of: STT joint OA without 1st CMC OA; 2nd MCP OA; 3rd MCP OA Scaphotrapeziotrapezoid joint OA (without 1st carpometacarpal OA), 2nd or 3rd metacarpophalangeal joint OA - at least 2 of these 3 patterns

Bilateral radiocarpal joint OA Osteoarthritis at the radiocarpal joints bilaterally

None of the above / no wrist or hand imaging performed

Imaging Evidence of CPPD in Symptomatic Joint(s)

0 pts

Linear or punctate calcification of fibrocartilage or hyaline cartilage in a symptomatic peripheral joint. Do not score calcification of the synovial membrane, joint capsule, or tendons. Advanced imaging (US, CT, DECT) is more sensitive than conventional X-ray.

Present on CR, US, CT, or DECT Imaging evidence of CPPD crystal deposition in a symptomatic peripheral joint on any modality

+16

None on CR (and US, CT, DECT not performed) Conventional X-ray was performed and negative; no advanced imaging available

None on US, CT, or DECT (and absent on CR or CR not performed) Advanced imaging (US/CT/DECT) performed and negative - strongest negative finding

-4

Number of Peripheral Joints with CPPD on Any Imaging

0 / 25 pts

Total count of peripheral joints (regardless of whether they are currently symptomatic) showing evidence of CPP crystal deposition on any imaging modality (CR, US, CT, or DECT). This is the single most influential domain - bilateral imaging significantly increases the potential score.

≥4 peripheral jointsFour or more joints with imaging evidence of CPP crystal deposition

+25

2-3 peripheral jointsTwo or three joints with imaging evidence of CPP crystal deposition

+23

1 peripheral jointA single joint with imaging evidence of CPP crystal deposition

+16

NoneNo peripheral joints with imaging evidence of CPPD

Scoring summary - Domain point values

Domain	Options	Score
A. Age at onset	≤60 / >60 years	0, +4
B. Time-course	None / persistent / 1 episode / >1 episode	0, +9, +12, +16
C. Sites	1st MTP / none / other / wrist / knee	-6, 0, +5, +8, +9
D. Metabolic diseases	None / present	0, +6
E. Synovial fluid	Not done / negative x1 / negative x≥2	0, -1, -7
F. OA hand/wrist	None / bilateral radiocarpal / STT+MCP pattern	0, +2, +7
G. Imaging in symptomatic joint	Positive / CR only negative / advanced negative	+16, 0, -4
H. Number of joints with CPPD	0 / 1 / 2-3 / ≥4	0, +16, +23, +25
Classification threshold		>56

CPPD Classification Calculator

Age at Onset of Joint Symptoms

Time-Course and Symptoms of Inflammatory Arthritis

Sites of Typical Episode(s) - Peripheral Joints

Related Metabolic Diseases

Synovial Fluid Crystal Analysis

OA of Hand / Wrist on Imaging

Imaging Evidence of CPPD in Symptomatic Joint(s)

Number of Peripheral Joints with CPPD on Any Imaging

Frequently Asked Questions

Domain Breakdown