Calcium Pyrophosphate Deposition Disease Workup
- Author: Constantine K Saadeh, MD; Chief Editor: Herbert S Diamond, MD more...
Approach Considerations
Revised diagnostic criteria for calcium pyrophosphate deposition disease (CPDD) are from Primer on Rheumatic Diseases (1997) and are used with permission from the Arthritis Foundation. The criteria are as follows[7] :
- Criterion I - Demonstration of calcium pyrophosphate crystal deposition in tissue or synovial fluid by definitive means (eg, characteristic radiographs, diffraction analysis, or chemical analysis)
- Criterion IIa - Identification of monoclinic or triclinic crystals showing no or weakly positive birefringence by compensated polarized light microscopy
- Criterion IIb - Presence of typical radiographic calcifications
- Criterion IIIa - Acute arthritis, especially of knees or other large joints
- Criterion IIIb - Chronic arthritis, especially of knee, hip, wrist, carpus, elbow, shoulder, or MCP joint, particularly if accompanied by acute exacerbation
In criterion IIIb, chronic arthritis shows the following features, which are helpful in differentiating it from osteoarthritis:
- Uncommon sites - Wrist, MCP joint, elbow, shoulder
- Radiographic appearance - Radiocarpal or patellofemoral joint-space narrowing, especially if isolated (eg, patella wrapped around the femur)
- Subchondral cyst formation
- Severity of degeneration - Progressive, with subchondral bony collapse and fragmentation with formation of intra-articular, radiodense bodies
- Osteophyte formation - Variable and inconsistent
- Tendon calcifications - Especially triceps, Achilles, obturators
Categories
Criteria-based categories include the following:
- Definite disease - Criterion I or IIa plus IIb must be fulfilled
- Probable disease - Criterion IIa or IIb must be fulfilled
- Possible disease - Criterion IIIa or IIIb should alert the clinician to the possibility of underlying calcium pyrophosphate deposition
Arthrocentesis
Arthrocentesis is the most important procedure to perform, especially in patients with acute pseudogout. The acquired fluid can be examined using compensated polarized microscopy, and fluid cultures can be performed.
Histologic Findings
Histologic changes associated with CPDD correspond to calcium deposits and to inflammation due to cartilage fragments. These changes are nonspecific, but calcium deposits inside the chondrocartilage are perhaps the most typical finding in patients with this condition. The pathognomonic finding with compensated polarized microscopy is the presence of weakly positively birefringent crystals, typically intracellular, that are usually rhomboid in shape.
Associated conditions
A number of conditions have been associated with CPDD. When CPDD is diagnosed, especially in a patient younger than 60 years, a metabolic workup should be performed, including measurements of serum calcium, magnesium phosphorus, alkaline phosphatase, iron, total iron-binding capacity, transferrin saturation and ferritin, and thyroid-stimulating hormone. Associated conditions include the following:
- True associations - Familial (autosomal dominant), prior trauma or prior surgery, hyperparathyroidism, hemochromatosis, hypophosphatasia, hypomagnesemia, aging
- Probable associations - Hypothyroidism, gout, familial hypercalciuria
- Possible associations - Acromegaly, diabetes mellitus, ochronosis, Wilson disease
Lab Studies
General laboratory studies usually are not helpful in calcium pyrophosphate deposition disease (CPDD). The white blood cell (WBC) count and erythrocyte sedimentation rate (ESR) may be elevated.
Evaluating for an underlying metabolic disease (eg, hemochromatosis, hyperparathyroidism, hypothyroidism) is reasonable, especially in younger patients.
Laboratory tests can include the following:
- Serum calcium, phosphorus, and magnesium and alkaline phosphatase levels
- Iron levels
- Total iron-binding capacity
- Transferrin saturation and ferritin
- Thyroid-stimulating hormone and free thyroxine levels
Pseudogout
Occasionally, pseudogout may present as a pseudoseptic syndrome with acute arthritis, fever, and leukocytosis with a left shift.
The diagnosis of acute pseudogout is made by performing compensated polarized microscopy after aspiration of fluid from the involved joint. The most commonly involved joint is the knee, followed by the wrist, the MCP joints, the elbows, and the MTP joints.
The crystals are rhomboid-shaped, weakly positively birefringent, and difficult to see. If intracellular, an acute attack of pseudogout is strongly suggested. Aspiration of the fluid from affected joints during an acute attack usually yields mildly to moderately inflammatory fluid, with 10,000-50,000 WBCs/µL, more than 90% of which are neutrophils. (See the images below.)
Calcium pyrophosphate deposition disease. Appearance of calcium pyrophosphate dihydrate crystals obtained from the knee of a patient with pseudogout. The crystals are rhomboid-shaped with weakly positive birefringence, as seen by compensated polarized microscopy. The black arrow indicates the direction of the compensator. 
Calcium pyrophosphate deposition disease. High-powered view of calcium pyrophosphate dihydrate crystals with compensated polarized microscopy. The black arrow indicates the direction of the compensator. Crystals parallel to the compensator are blue, while those perpendicular to the compensator are yellow. 
Calcium pyrophosphate deposition disease. High-powered view of calcium pyrophosphate dihydrate crystals with compensated polarized microscopy. The crystals parallel to the compensator were blue, while those perpendicular to the compensator were yellow. However, the crystals have been rotated 90%, resulting in a color change in both of them. The direction of the compensator was not changed and is indicated by the black arrow. Gout and pseudogout can coexist, even in the same joint; therefore, the presence of gout does not rule out the possibility of pseudogout and vice versa. Ultrasonography may be helpful in diagnosing pseudogout. (See the image below.)
Wrist chondrocalcinosis. Pseudorheumatoid arthritis
The ESR is usually elevated in pseudorheumatoid arthritis. The older age at onset for this condition, the lack of rheumatoid factor, and the presence of chondrocalcinosis help to differentiate it from true rheumatoid arthritis. However, rheumatoid arthritis can occur in older individuals. In addition, older individuals may have low-titer–positive rheumatoid factor. Thus, the diagnosis must be made with care.
Imaging Studies
Radiography
Radiologic studies are important in the diagnosis of CPDD, with radiography being the criterion diagnostic standard (see the images below). Imaging studies usually include the hands, wrists, pelvis, and knees. The pelvic radiograph should include an anteroposterior view that shows the symphysis pubis and hips.
Calcium pyrophosphate deposition disease. Radiograph of the knee showing chondrocalcinosis involving the meniscal cartilage, as well as evidence of osteoarthritis. 
Calcium pyrophosphate deposition disease. Radiograph of the wrist and hand showing chondrocalcinosis of the articular disc of the wrist and atypical osteoarthritis involving the metacarpophalangeal joints in a patient with underlying hemochromatosis. Chondrocalcinosis is usually found in the articular cartilage or meniscal cartilage of the knee, the triangular ligament of the wrist, the symphysis pubis, or the glenoid or acetabulum labra. Chondrocalcinosis has also been noticed in other areas of the wrist (aside from the fibrocartilage), such as the distal radioulnar joint and the midcarpal joint, as well as in the pisotriquetral joint. In addition, it has been reported in the spine as calcification of the ligamentum flavum.[8]
In some situations, hemochromatosis can produce specific radiographic findings, such as large, hooklike osteophytes, especially around the second to fifth MCP joints. However, these findings also can occur in patients with CPDD alone.
Hooklike osteophytes are a common radiologic finding in patients with a pseudo-osteoarthritis condition and are usually present along the second and third metacarpal heads.
Radiologically, erosions can be observed in pseudorheumatoid arthritis but are usually associated with chondrocalcinosis.
MRI and ultrasonography
Routine magnetic resonance imaging (MRI) has not been shown to be as sensitive as radiography in detecting the presence of CPPD deposits. However, 4T MRI holds better promise in detecting these crystals.
Ultrasonography has been significantly beneficial in the visualization of CPDD crystals.[9] (See the image below.)
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