Osteitis deformans, also known as Paget's disease, is a condition frequently observed in elderly patients, despite the fact that it's prevalence has decreased over the last 20 years. With unclear etiology, this pathological entity is characterized by abnormal behavior of osteoclasts and osteoblasts, leading to pathological bone formation. The disease may involve one or more sites and may progress to fractures, osteosarcoma and cardiovascular abnormalities.
This disease has an ongoing character, may involve one or more bones at first, but secondary dissemination does not occur.
Patients may be asymptomatic or may have complaints such as bone pain, that is dull, quasi-permanent and accentuated during the night and with weight burden. Uninvolved areas may also hurt, because of the redistribution of the mechanical forces.
Involved bones may present with deformities like bowing. With skull implication, symptoms like headaches, hearing loss, vertigo, tinnitus, changes in vision and cranial nerve palsies occur. If the cranium descends onto the cervical spine, patients experience paresthesias and bowel or bladder incontinence. Other cranial complications include hydrocephalus and subsequent brain compression symptoms: syncope, nausea, ataxia, dementia.
Facial bones may also undergo changes, leading to occlusion abnormalities and loss of teeth.
As axial bones are more frequently affected, patients usually describe lower back, cervical or hip pain. Fractures and arthritis are not uncommon, but if the pain is constantly increasing and the surrounding tissues become swollen, a radiography should be performed in order to exclude osteosarcoma.
Osteitis deformans is characterized by increased vascularization of the affected areas. This can lead to high-output heart failure in patients with decreased contractility reserve . Arteriosclerosis and mitral and aortic valve calcifications have been shown to be related to disease progression and further worsen cardiovascular status   .
Asymptomatic patients also have no clinical signs of the disease. Physical examination may, however, reveal deformed or bowing bones, kyphosis (that may cause spinal cord compression and injury), warm teguments over the affected area, increased skull circumference, facial deformity or narrowing of the airways. Brain compression results in ataxia or dementia, while cranial nerve VII compression leads to deafness and vertigo. Patients may also present fractures as the first sign of disease.
Blood workup should include serum and bone-specific alkaline phosphatase, procollagen I N -terminal peptide and serum total acid phosphatase, all of which may be increased . Even if serum alkaline phosphatase is normal, the disease cannot be excluded. Calcium and phosphate levels are usually normal in mobile patients but may be high if hyperparathyroidism coexists. Secondary hyperparathyroidism may appear due to increased calcium demand. Hyperuricemia has also been described .
Urine should be examined for specific markers like hydroxyproline, deoxypyridinoline, C-telopeptide (CTx) and N-telopeptide (NTx) . Alpha-CTx/beta-CTx ratio is high in active disease patients and is a suitable marker to monitor therapy .
Plain radiographs are used both for disease and complication diagnose and monitoring, but the gold standard in documenting the extent of the pathological process is represented by Tc99m-MDP scintigraphy, despite the fact that this method is less specific than classical radiology. Computer tomography and magnetic resonance imaging are useful when trying to evaluate malignant transformation, nerve compression, and hydrocephalus.
Bone biopsy reveals the typical mosaic pattern  that appears as a result of osteolysis, bone formation, and osteosclerosis. The architecture is disorganized and vascularization is abundant. In time, osteosclerosis becomes the most prominent feature.