Paget’s disease of bone is a chronic disorder that disrupts the normal process of bone remodeling, leading to abnormally structured and weakened bone tissue. The condition primarily affects adults over the age of 50, involving an accelerated and disorganized cycle of bone breakdown and regrowth. This abnormal activity results in bones that are enlarged, porous, and prone to fracture and deformity. Diagnosis involves a combination of physical indications, measuring specific substances in the blood, and utilizing detailed medical imaging.
Early Signs and Reasons for Testing
Most individuals with Paget’s disease do not experience symptoms, and the condition is often discovered unintentionally during routine medical evaluations for other health concerns. This incidental discovery might occur when a patient receives a standard blood test or an X-ray for an unrelated issue, revealing signs of the disorder.
When symptoms are present, the most frequent complaint is bone pain, which can be a deep, aching sensation that worsens at night or with rest. The location of the pain depends on the bones affected, commonly including the pelvis, spine, skull, and long bones of the limbs.
Visible changes or complications often prompt a visit to a healthcare provider. Abnormal bone growth can lead to deformities, such as the bowing of a leg bone or enlargement of the skull. If the affected bone compresses nearby nerves, a patient may experience neurological issues, including hearing loss, headaches, or radiating pain, tingling, and numbness in a limb. These signs warrant specific diagnostic testing to confirm Paget’s disease.
Blood Markers Used for Detection
The initial biochemical evidence of Paget’s disease is typically found through a blood test measuring Serum Alkaline Phosphatase (ALP). ALP is an enzyme produced by various tissues, including the liver and bone. Its concentration rises significantly in Paget’s disease due to the disorder’s effect on bone metabolism, involving hyperactive bone-resorbing cells (osteoclasts) followed by overcompensation from bone-forming cells (osteoblasts).
This rapid production of new, disorganized bone tissue by the osteoblasts releases large amounts of ALP into the bloodstream. An elevated total ALP level provides strong evidence of increased bone turnover, characteristic of active Paget’s disease. Since the liver also contributes to total ALP, additional testing may be required to pinpoint the source of the high enzyme level.
To confirm that the elevated ALP is specifically bone-related, a clinician may order a test for bone-specific alkaline phosphatase (BALP), which isolates the enzyme originating from the osteoblasts. Another marker reflecting the high turnover rate is N-terminal propeptide of type I procollagen (P1NP), a substance released during new bone collagen formation. While a high ALP or BALP level suggests the disease, it must be paired with imaging to provide a definitive diagnosis and map the extent of the affected skeleton.
Visual Confirmation Through Imaging
Once blood tests indicate heightened bone turnover, medical imaging is necessary to confirm the diagnosis and visualize the structural changes caused by Paget’s disease. Standard X-rays play a role, clearly showing characteristic structural abnormalities in the affected bones. These images often reveal bone enlargement and a thickened outer layer, known as the cortex.
X-rays can display the different phases of the disease, showing areas of bone breakdown (lytic lesions) and excessive bone formation (sclerotic lesions). In the skull, chaotic bone growth may present as a mottled, dense pattern described as a “cotton wool” appearance. In the long bones, a distinct, advancing lytic edge can sometimes be seen, described as a “blade of grass” or “flame-shaped” lesion.
While X-rays show the structure of the disease in a specific location, a radionuclide bone scan is the preferred method for determining the full extent and metabolic activity of the disorder throughout the skeleton. This procedure involves injecting a small amount of a radioactive tracer into the bloodstream, which is absorbed by bones experiencing high turnover. Active sites of Paget’s disease “light up” brightly on the scan, making it a sensitive tool for identifying all metabolically affected bones, even those without significant structural changes visible on an X-ray. The combination of biochemical evidence and visual confirmation allows for a complete and definitive diagnosis.