Hyperparathyroidism

Hyperparathyroidism is a disease of increased bone resorption and bone formation. Subsequently, plain radiographic findings may include resorption and sclerosis of numerous sites in the skeletal system.

Historically, osteitis fibrosa cystica was used to describe the advanced skeletal disease in primary hyperparathyroidism. Bone findings were characterized by the osteoclastic resorption of bone, osteoblastic bone formation, and fibrous replacement of marrow, with radiographic findings of subperiosteal resorption, brown tumors, bone cysts, and sclerosis.

These days, the most common radiologic finding in primary hyperparathyroidism is osteopenia, which may be generalized or asymmetric. Fine trabeculations are initially lost, with resultant coarse and thickened trabeculae. The disease may progress with further destruction that results in a ground-glass appearance in the trabeculae. About 30-50% of the bone density must be lost to show changes on radiographs. Other methods for the quantification of bone density, such as QCT scanning and DXA, are more sensitive in the evaluation of osteopenia.

Additional findings include bone resorption, which may occur at many different anatomic sites. Bone resorption may be classified as subperiosteal, intracortical, trabecular, endosteal, subchondral, subligamentous, or subtendinous. Subperiosteal bone resorption is an early and virtually pathognomonic sign of hyperparathyroidism, and this finding is marked by marginal erosions with adjacent resorption of bone and sclerosis. An unusual lacelike appearance may be seen beneath the periosteum with an occasional spiculated external cortex. The underlying resorptive process may progress to complete cortical disappearance.

Although subperiosteal bone resorption can affect many sites, the most common site in hyperparathyroidism is the middle phalanges of the index and middle fingers, primarily on the radial aspect.

After resection of an adenoma, lesions may become sclerotic on radiographs. Once considered a finding that was characteristic of primary hyperparathyroidism, brown tumors are more common in secondary hyperparathyroidism because of the increasing population and life expectancy of patients undergoing dialysis.

Calcium pyrophosphate dihydrate crystal deposition disease (CPPD) is more common in association with primary hyperparathyroidism than with secondary hyperparathyroidism. Chondrocalcinosis may affect the menisci of the knee, the triangular cartilage of the wrist, and the symphysis pubis. CPPD arthropathy is less common in these patients than in patients with idiopathic disease.

Other radiographic findings in primary hyperparathyroidism include varying degrees of sclerosis, although generalized sclerosis is more common in secondary hyperparathyroidism. Soft-tissue and vascular calcification is more common in secondary disease, as is superior and inferior band sclerosis of the spine, which is called rugger-jersey spine. The laxity of ligaments and tendons primarily affects the sacroiliac and acromioclavicular joints, whereas rupture may be seen at several sites, including the quadriceps, triceps, and patellar tendons.

In the setting of elevated serum calcium levels and elevated PTH levels, the diagnosis of primary hyperparathyroidism is certain. However, radiographic findings of subperiosteal resorption are most specific for the disease and should prompt consideration of the primary hyperparathyroidism.