(See also Overview of Crystal-Induced Arthritides Overview of Crystal-Induced Arthritides Arthritis can result from intra-articular deposition of crystals: Monosodium urate Calcium pyrophosphate dihydrate Basic calcium phosphate (apatite) Rarely, others such as calcium oxalate crystals read more .)
CPPD crystal deposition (chondrocalcinosis, pyrophosphate arthropathy), whether symptomatic and asymptomatic, becomes more common with age.
Asymptomatic chondrocalcinosis is common in the knee, metacarpophalangeal joints, hip, wrist, annulus fibrosus of the intervertebral disks, symphysis pubis, and spine. Men and women are affected about equally. The incidental detection of chondrocalcinosis on plain x-rays or other imaging does not mean that the patient should be treated for CPP arthritis.
Etiology of Calcium Pyrophosphate Arthritis
The cause of CPP arthritis is unknown. CPP arthritis is frequently associated with other conditions, such as trauma (including surgery), hypomagnesemia Hypomagnesemia Hypomagnesemia is serum magnesium concentration 1.8 mg/dL ( 0.70 mmol/L). Causes include inadequate magnesium intake and absorption or increased excretion due to hypercalcemia or drugs such... read more , hyperparathyroidism Pathophysiology Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism, vitamin... read more , gout Gout Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more , hemochromatosis Hereditary Hemochromatosis Hereditary hemochromatosis is a genetic disorder characterized by excessive iron (Fe) accumulation that results in tissue damage. Manifestations can include systemic symptoms, liver disorders... read more , hypophosphatasia Congenital Hypophosphatasia Congenital hypophosphatasia is absence or low levels of serum alkaline phosphatase due to mutations in the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). Because serum alkaline... read more , Gitelman syndrome Bartter Syndrome and Gitelman Syndrome Bartter syndrome and Gitelman syndrome are autosomal recessive renal disorders characterized by fluid, electrolyte, urinary, and hormonal abnormalities, including renal potassium, sodium, chloride... read more , X-linked hypophosphatemic rickets Hypophosphatemic Rickets Hypophosphatemic rickets is a disorder characterized by hypophosphatemia, defective intestinal absorption of calcium, and rickets or osteomalacia unresponsive to vitamin D. It is usually hereditary... read more , familial hypocalciuric hypercalcemia Familial hypocalciuric hypercalcemia Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism, vitamin... read more , and old age. These associations suggest that calcium pyrophosphate dihydrate (CPPD) crystal deposits may be caused by degenerative or metabolic changes in the affected tissues.
Some cases are familial, usually transmitted in an autosomal dominant pattern, with complete penetration by age 40.
The ankyrin (ANK) protein is a central factor in producing excess extracellular pyrophosphate, which promotes CPPD crystal formation. ANK protein is a transporter of intracellular and microvesicle pyrophosphate to the extracellular location where CPPD crystals form.
Symptoms and Signs of Calcium Pyrophosphate Arthritis
Acute, subacute, or chronic arthritis can occur, usually in the knee, wrist, or other large peripheral joints; thus, calcium pyrophosphate crystal disease can mimic many other forms of arthritis. Acute flares are similar to gout but vary more in intensity, tend to be more protracted, and are often more difficult to treat. There may be no symptoms of CPP arthritis between flares or continuous low-grade symptoms in multiple joints, similar to rheumatoid arthritis or osteoarthritis. These patterns tend to persist for life.
Crowned dens syndrome (with a radiographically "crowned" appearance of the odontoid process of the second cervical vertebra) is a presentation of acute CPP axial arthritis in which there can be profound inflammatory neck pain and stiffness. It can be mistaken for polymyalgia rheumatica, giant cell arteritis, seronegative spondyloarthritis, cervical osteomyelitis, or meningitis.
Diagnosis of Calcium Pyrophosphate Arthritis
Synovial fluid analysis
Identification of crystals microscopically
CPP arthritis should be suspected in older patients with arthritis, particularly those with a history of recurrent inflammatory arthritis.
Diagnosis of CPP arthritis is established by identifying rhomboid- or rod-shaped crystals in synovial fluid Microscopic Examination of Crystals in Joints that are not birefringent or are weakly positively birefringent on polarized light microscopy. Joint fluid in acute flares has findings typical of inflammation; thus, coincident infectious arthritis and gout (other common causes of inflammatory joint fluid) must also be excluded. Infectious arthritis is ruled out based on Gram stain and culture findings. Gout is best ruled out by the absence of urate crystals in fluid from the inflamed joint. Notably a patient may have both gout and CPP arthritis. X-rays or ultrasonography are indicated if synovial fluid cannot be obtained for analysis; findings of multiple linear or punctate calcification in articular cartilage, especially fibrocartilage, support the diagnosis, but do not exclude gout or infection.
Prognosis for Calcium Pyrophosphate Arthritis
The prognosis for individual flares of acute CPP arthritis is usually excellent. However, chronic arthritis can occur, and severe destructive arthropathy resembling neurogenic arthropathy Neurogenic Arthropathy Neurogenic arthropathy is a rapidly destructive arthropathy due to impaired pain perception and position sense, which can result from various underlying disorders, most commonly diabetes and... read more (Charcot joints) occasionally occurs. Unlike gout, chronic CPP arthritis is challenging to manage because there is no therapy that effectively eliminates or reduces the burden of CPPD crystals. Patients, especially younger ones, who have frequent CPPD flares should be evaluated for underlying triggers and diseases Etiology Calcium pyrophosphate arthritis (CPP arthritis) involves intra-articular and/or extra-articular deposition of calcium pyrophosphate dihydrate (CPPD) crystals. Manifestations are protean and... read more .
Treatment of Calcium Pyrophosphate Arthritis
Oral corticosteroids (eg, prednisone, methylprednisolone)
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Interleukin-1 (IL-1) antagonists (eg, anakinra)
Treatment of acute CPP arthritis is similar to that for acute gout Treatment Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more . Symptoms of acute synovial effusion abate with synovial fluid drainage and instillation of a microcrystalline corticosteroid ester suspension into the joint space (eg, 40 mg prednisolone acetate or prednisolone tertiary butylacetate into a knee).
Indomethacin, naproxen, or another NSAID Nonopioid Analgesics Nonopioid and opioid analgesics are the main drugs used to treat pain. Antidepressants, antiseizure drugs, and other central nervous system (CNS)–active drugs may also be used for chronic or... read more given at anti-inflammatory doses often stops acute flares. Colchicine treatment of acute flares Treatment of acute flares Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more is identical to that of gout. Colchicine 0.6 mg orally once a day or 2 times a day may decrease the frequency of recurrent acute flares. Oral corticosteroids are effective at treating acute CPP arthritis flares and are particularly useful for patients in whom oral NSAIDs and colchicine are contraindicated. However, failure to resolve an acute flare may require a higher dose for a longer period of time. Interleukin-1 antagonists such as anakinra can also be effective.
Asymptomatic chondrocalcinosis becomes more common with age, particularly in the knee, hip, wrist, annulus fibrosus of the intervertebral disks, and symphysis pubis but does not require treatment.
CPP arthritis can affect the knee and large peripheral joints and mimic other forms of arthritis (eg, gout, rheumatoid arthritis, osteoarthritis).
Examine joint fluid for characteristic rhomboid- or rod-shaped crystals in synovial fluid that are not birefringent or are weakly positively birefringent, and exclude joint infection.
For acute symptoms, treat with an intra-articular corticosteroid, an oral NSAID, colchicine, or oral corticosteroids; anakinra can also be effective.
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