Our bones are composed of cells called osteoclasts necessary to the bone-forming process. Osteoclasts break down bone, creating microscopic pits and osteoblasts, which form new bone to fill these holes.

This process of bone formation and absorption, called “bone remodeling”, continues throughout our life and when in balance, bone mass and structure remain normal and stable.

Osteoporosis and Paget’s disease are both bone remodeling disorders. However, osteoporosis creates diffused bone loss when absorption surpasses bone formation, while Paget’s disease refers to a localized “bone remodeling” disorder that can affect one or more bones in our body.

Paget’s disease was discovered 125 years ago by Sir James Paget. It occurs when osteoclasts at affected sites abnormally increase in size and number, which is thought to be caused by viral and genetic predisposing factors.

Characterized by abnormal increases in both osteoclastic bone absorption and subsequent osteoblastic bone formation, Paget’s is known for bone thickening, hardening and enlargement, making them prone to deformity and fracture.

In the United States, about 3 percent of the population, usually over the age of 55, develops Paget’s disease. Both men and women are equally affected.

Initially, most patients with Paget’s disease are asymptomatic (without symptoms). However, as the disease progresses, it follows an alternating pattern of remission and flare-ups, which over time, increase in frequency.

The main complaints of patients with Paget’s disease are bone deformity and pain, most commonly of the skull, spine and lower extremities. Skull involvement can cause increased skull size, in turn leading to hearing loss, while involvement of the lower extremities and spine can create bowing of the legs, spinal stenosis, degenerative arthritis of the spine or hip, and even fracture.

The most serious complication of Paget’s disease is the development of a sarcoma (cancer) in a Paget’s skin lesion. Fortunately, sarcoma is rare and only affects about 1 percent of patients.

Diagnosis can be made via bone scan followed by radiographic evaluation. Treatment includes bisphosphonates, such as alendronate (Fosamax) and risedronate (Actonel), which can incorporate into bone, thereby impeding osteoclastic bone reabsorption while decreasing bone turnover and maintaining remission.

A blood test called “serum alkaline phosphatase” is a marker of bone turnover and is used to both monitor disease activity and serve as a treatment guide.

Because osteoporosis and Paget’s disease are commonly seen in the elderly, it is not unusual to see patients with both Paget’s disease and osteoporosis. Although bisphosphonates can be used to treat both of these disorders, dose and directions are quite different.

For the treatment of Paget’s disease, Fosamax 40 mg every day for 6 months is recommended. Even though Paget’s disease cannot be cured, the correct treatment can decrease symptoms and lead to prolonged periods of remission.

— Dr. Yong H. Tsai is board-certified in rheumatology, allergy and clinical immunology and has been practicing in this area since 1993. His website is arthritis-allergy.net.