The PHPT is a relatively common endocrine disorder, which is usually presented by incidental detection of hypercalcemia (
1, 3). Although osteitis fibrosa is the characteristic presenting abnormality, in recent years, this skeletal disorder has become rare as the first presenting feature. However, osteopenia is still a common and important feature of PHP, and histopathologic studies and measurements of BMD have demonstrated stimulated bone resorption and a high-turnover bone loss, which is more dominant in cortical bones than in cancellous bones ( 3).
The PHPT is characterized by decalcification of the bone and is especially prominent in the subperiosteal region, leading to a granular appearance of the calvarium due to the loss of central (diploic) trabeculae and thinning of the cortical tables in more advanced cases. This change in the normal trabecular pattern results in the classic homogeneous ground glass-like or salt-and-pepper appearance (
In jaws, demineralization and thinning of the cortical tables leads to decreased density and the consequent radiolucent appearance of the jaws that contrasts with the density of the teeth. This demineralization and thinning often occur in cortical boundaries such as the inferior border of the mandibular canal and the cortical outlines of the maxillary sinuses (
As mentioned earlier, the usual skeletal manifestation, when present, is diffuse osteopenia; osteosclerosis is rare in adults with PHPT (
5). On the other hand, in secondary hyperparathyroidism associated with renal osteodystrophy, diffuse osteosclerosis is not uncommon ( 5).
In children, PHPT has been frequently associated with intense osteosclerosis of the metaphyseal regions, particularly in rapidly growing bones. Localized osteosclerosis mixed with lytic deposits in the skull and in the vertebral bodies adjacent to the endplates, and also increased trabecular bone in the metaphyses of the long bones, has been reported in rare occasions in adults with PHPT; however, the exact mechanism of bone sclerosis in PHPT has not been clearly defined (
5). An experimental study has demonstrated the production of dense metaphyseal bone in rats given small doses of PTH over an extended period, which was confirmed quantitatively by BMD measurement. In addition to stimulating osteoclastic activity and bone resorption, PTH has been shown to stimulate osteoblastic activity and to increase bone-forming surfaces ( 5).
Very rare cases of focal hyperostotic lesions (or focal osteosclerosis) have been described in patients with PHPT, and its mechanism has remained unknown (
6). Although focal osteosclerosis was observed in the skull of some patients with PHPT on plain films in the days when diagnosis of PHPT was difficult, osteosclerosis in patients with PHPT has been unusual recently, since diagnosis of PHPT has become increasingly easy ( 4).
The diseases that can be found in differential diagnosis with sclerosis in hyperparathyroidism are osteopetrosis, renal osteodystrophy, Paget’s disease, and florid cemento-osseous dysplasia (FLCOD).
Osteopetrosis or "marble bone disease" is a congenital condition characterized by a diffuse, bilateral, and symmetric significant increase in the density of all bones. This increased density throughout the skeleton is homogeneous and diffuse (
1, 2, 7). However, only the mandible and skull bones showed sclerosis in our patient, and other bones in the skeleton had almost normal or evenly decreased density.
Bone changes in renal osteodystrophy result from secondary hyperparathyroidism due to chronic renal failure (
1). Affected patients often have increased levels of PTH secondary to a prolonged low serum level of calcium as a result of impaired calcium absorption and a high serum level of phosphor, resulting from a reduction in renal phosphorus excretion. Skeletal changes include generalized loss of bone density, thinning of bony cortices, and occasionally, an increase in bone density ( 1). In our case, laboratory data revealed no renal disease.
Paget’s disease is seen most frequently in Great Britain and Australia, whereas it is rare in Africa and Asia (
1, 7). The affected bones become enlarged and commonly deformed, resulting in bowing of the weight-bearing bones, such as the legs, curvature of the spine, and enlargement of the skull and the jaws (monkey-like) ( 7).
Malocclusion may occur due to the separation and movement of teeth. Serum levels of ALP are severely increased in most cases (
1). Our patient did not have enlargement and deformity of the bones, as seen in Paget’s disease. She had a mild increase in serum levels of ALP (up to three times the upper limit of normal), but it was not as severe as the increase in ALP seen in Paget’s disease.
Florid osseous dysplasia lesions are usually bilateral and present in both jaws. However, the mandible is the more common location when the lesions are present in only one jaw. The lesions occur above the inferior alveolar canal of the mandible. They usually have well-defined peripheries and sclerotic borders that can vary in width, and also a soft tissue capsule, which may not be apparent in mature lesions (
1, 2, 8). In our case, not only the area above the inferior alveolar canal, but also the area under this canal was involved. In addition, there was no lesion with a well-defined border or soft tissue capsule because the sclerosis had a more disseminated pattern. Furthermore, FLCOD only involves the jaw, but our patient had skull involvement, too.
In this case, the development of sclerosis in the jaws and skull radiographs has been demonstrated in a patient with PHPT. Although the association is rare, a causal relationship between parathyroid hormone excess and osteosclerosis has been suggested due to clinical and radiographic findings.