Calcium hydroxyapatite deposition disease is a condition where there is deposition of calcium phosphate crystals, mainly hydroxyapatite in the soft tissues around the joint especially tendons.
Calcific tendinitis is the term given to it in the shoulder when the deposition involves supraspinatus tendon. However, the term calcific periarthritis denotes the condition better as the deposits may also be found in tissues other than tendons.
Other names in use for this condition are peritendinitis calcarea, hydroxyapatite rheumatism etc.
Calcium hydroxyapatite is the most abundant form of calcium in human bone and the deposition of hydroxyapatite and other basic calcium phosphate crystals occurs as a primary or idiopathic entity and as a secondary process in a number of conditions like an end-stage renal disease, collagen vascular diseases, Vit D intoxication, tumoral calcinosis. Dystrophic calcifications are also largely calcium hydroxyapatite.
Calcium hydroxyapatite deposition disease is a type of crystal deposition like gout and calcium pyrophosphate dehydrate deposition disease and there appears to be considerable overlap among these crystal deposition diseases.
Pathogenesis of Calcium Hydroxyapatite Deposition Disease
The pathogenesis is still not clear. Trauma, abnormal pressure, compression, decreased local vascularity, local hypoxia, and preexisting tissue degeneration have been suggested as possible initiating factors.
Three phases of the condition have been identified. Here the description is of the shoulder joint.
Silent phase
This is the initial phase in which calcium deposit is completely contained within the tendon which appears sharply defined circumscribed. Patients do not have any symptoms in this phase.
Mechanical Phase
The mechanical phase is characterized by enlargement of the deposits which may produce impingement like symptoms. Liquefaction of the deposits occurs leading to an increase in pressure and bursitis. The deposit is still within the tendon.
Recurrent bursitis may lead to rupture of the deposit, either under or inside the bursa. This stage is characterized by acute painful attacks.
Adhesive Periarthritis
It is a late stage, is characterized by general debility, pain, limitation of motion. Variable sized calcium deposits within a rotator cuff that shows considerable destructive changes.
Presentation of Calcium Hydroxyapatite Deposition Disease
Calcium hydroxyapatite Deposition Disease or Calcific periarthritis most commonly affects a middle-aged person.
Males are slightly more affected than females. The patients with these deposits could be asymptomatic or may present recurrent symptoms of pain and disability of varying severity. An acute presentation is also known.
Although the shoulder region by far the common site for Calcium hydroxyapatite deposition, these deposits occur in the number of other sites.
The periarticular deposition has been found nearly all joints as well as in a number of tendon insertions remote from joints. The shoulder is the most commonly involved joint followed by hip, elbow, wrist, and knee.
Tendinous Calcium hydroxyapatite deposits loosely occur close to the site of tendon insertion near the joint though distant deposits have been noted. For example in the gluteus maximus insertion, adductor magnus insertion, and pectoralis major insertion.
Lab Studies
The results of laboratory tests are usually normal.
Individual calcium hydroxyapatite molecules are small and they not visible with light microscopy except as aggregates which may appear glossy but non-birefrigerant in polarized light.
Transmission electron microscopy of electron diffraction studies may be used to specifically identify Calcium hydroxyapatite crystals but have limited access.
Imaging
On x-rays, calcium hydroxyapatite deposits are homogenous amorphous densities and lack trabeculations which allows them to be different from heterotropic ossification or accessory bones. Size could be variable. They are roughly ovoid in shape or linear or triangular with smooth and ill-defined margins.
CT or MRI may be needed for the differentiation of lesions from other conditions. Chondrocalcinosis may be noted
Occasionally, calcific periarthritis may produce erosions of bone immediately beneath the insertion of the involved tendon. The cause of the erosions is not known.
Intrarticular Calcium hydroxyapatite Deposition Disease [Milwaukee Shoulder]
This is also called apatite associated destructive arthritis. This is destructive arthropathy of the shoulder associated with chronic tears of the rotator cuff and joint effusions containing hydroxyapatite crystals activated collagenases, neutral proteases.
Most commonly affected patients are elderly women and usually involves dominant shoulder.
Though the cause is not exactly clear, it is thought that crystal deposition in the joint causes the release enzymes like collagenases, serine proteases, elastases, and interleukin-1. This leads to a decrease in joint function and degradation of joint anatomy.
The involved shoulder is usually swollen and may be painless or painful. Aspiration of the joint may yield large amounts of synovial fluid, frequently tinged with blood. The fluid contains hydroxyapatite crystals in aggregates, activated collagenases, neutral proteases, and particulate collagen.
Sometimes calcium pyrophosphate dihydrate crystals are also often found in the fluid supporting the theory that Milwaukee shoulder syndrome may represent a mixed disease.
X-rays reveal destroyed joint, glenohumeral joint destruction, narrowing and sclerosis with ossification cyst formation. Upward subluxation of the humeral head due to disruption of the rotator cuff may be evident.
Knee involvement is common in patients with Milwaukee shoulder syndrome [50%] where radiographic appearance at this site is very similar to that calcium pyrophosphate arthropathy and distinguishing could be difficult. The two may also coexist as a mixed crystal deposition disease.
Differential Diagnosis of Calcium Hydroxyapatite Deposition Disease
Other crystal deposition like pseudogout [calcium pyrophosphate dihydrate deposition disease] and gout may be similar in presentation and imaging to calcium hydroxyapatite deposition disease and may have periarticular depositions.
Metastatic calcification may occur in periarticular locations in a number of diseases with end-stage renal disease and renal osteodystrophy, hyperparathyroidism, hypervitaminosis D and tumoral calcinosis.
The underlying disease or large size of the calcification should allow differential from calcium hydroxyapatite deposition disease
Collagen vascular diseases such as scleroderma and dermatomyositis may show soft tissue calcifications.
Heterotropic ossifications secondary to trauma may occur in periarticular locations. Trabeculae may be present unlike calcium hydroxyapatite deposition disease
Tumor and tumor-like conditions like synovial osteochondromatois may be associated with calcifications within periarticular soft tissue masses. The presence of the significant soft tissue mass and possible articular erosion may help distinguish these entities.
Synovial sarcomas arise in periarticular locations and contain calcifications in one-third of cases. Bone erosions may be present.
Treatment of Calcium hydroxyapatite Deposition Disease
Treatment of calcium hydroxyapatite deposition disease is nonspecific.
Acute attacks of synovitis may be self-limiting, resolving in from days to several weeks.
Aspiration of effusions and the use of either nonsteroidal anti-inflammatory agents is the prescribed treatment.
Oral colchicines for 2 weeks or of intraarticular injection of steroids appear to shorten the duration and intensity of symptoms.
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