disease is a condition of dysregulated and abnormally excessive bone
remodeling, characterized by increased bone destruction and bone formation. The
resulting new bone is dense, yet structurally fragile. The spine, skull, pelvis
and femur (see Figure 1) are the most common locations.
Many patients with Paget’s disease have no symptoms and are made aware that they have the disease when x-rays, taken for some other reason, reveal it.
During normal bone remodeling, there is a balance between bone resorption by osteoclasts and new bone formation by osteoblasts. In Paget’s disease, there is increased bone resorption by the osteoclasts. While the exact cause is unknown, there is speculation that Paget’s disease is linked to viral infection.
Paget’s disease encompasses three phases: lytic, mixed, and sclerotic. During the lytic phase, osteoclastic resorption predominates, while during the sclerotic phase, osteoblastic bone formation predominates. In the mixed phase, there is both bone resorption and formation occurring. All three phases of Paget’s disease may occur simultaneously in different parts of the same bone.
Bone overgrowth may cause pain, arthritis, and deformities (the latter giving rise to the name osteitis deformans).
Bone overgrowth may cause compression on nearby nerves leading to a loss of sensation or motor function. Compression of the 8th cranial nerve can cause sensorineural hearing loss; indeed, in one review a majority of people with Paget’s disease had some degree of hearing loss (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515478/).
The bone is also susceptible to fracture.
Very rarely, a region of bone affected by Paget's disease can undergo malignant transformation and become a sarcoma.
Because osteoclasts are overactive in Paget’s disease, there may be elevated calcium levels in the blood (hypercalcemia). Hypercalcemia symptoms have been summarized by the phrase "stones, bones, groans, and moans,” respectively referring to nephrolithiasis (kidney stones), bone symptoms (as mentioned above), gastrointestinal symptoms of constipation and nausea (among others), and psychiatric symptoms.
Paget’s disease is also associated with increased cardiac output and left ventricular hypertrophy if the degree of Paget disease is extensive. Increased vascularity of affected tissue is thought to be the cause. High-output congestive heart failure may therefore occur.
Additional Points to Consider
- Paget’s disease is named after Sir James Paget (Figure 2), who also described what is now called “Paget's disease of the breast,” a form of breast cancer involving the nipple. Paget is additionally credited for forming the first journal club.
- The composer, Ludwig Van Beethoven, might have become deaf because of Paget’s disease, as argued in the paper Paget's Disease and Beethoven's Deafness by SV Naiken in Clinical Orthopaedics and Related Research (1972) 89:103-105.
- Standardized test writers are not happy if you merely knew that a patient’s head getting larger (i.e., “my hat no longer fits”) might be due to acromegaly/excess of growth hormone. They want you to know that Paget’s disease in the skull can be a cause as well.