A chronic disorder of the bone characterized by repeated episodes of increased bone resorption followed by excessive attempts at repair which results in weakened deformed bones of increased mass. The condition is also referred to as Paget's disease of the bone and is the second most common metabolic bone disease after osteoporosis.

The exact cause is unknown. It has been thought that an early viral infection with the mumps infection may cause a dormant skeletal infection that erupts years later as Paget's disease. The disease may occur in families.

The condition usually occurs in persons over forty years of age with mild symptoms, or it may occur without symptoms. The new, excessive abnormal bone formation results in a fragile, weak bone, which causes severe persistent pain with deformities of the external and internal structure. The pain intensifies with weight bearing and may impair movement. Head enlargement occurs over the frontal and occipital areas, with the person noting an increase in hat size. Headaches are present as the skull becomes involved. There may be impaired hearing and visual acuity; kyphosis; stiffness; and bowed leg bones. Frequent fractures occur at the location of the disease process. The sites may be warm and tender with periosteal tenderness. Spinal cord compression may result in spinal narrowing, or partial or complete paralysis. X-rays show dense expanded bones. The disorder is usually localized in one or more areas of the skeleton, with occasionally widely distributed skeletal deformities.

Tests conducted include: x-rays, computed tomography (CT) scan; biopsy; 24-hour urine analysis; and complete blood count (CBC).

Persons who are asymptomatic require no treatment. Prophylactic treatment is done to prevent deafness and a stroke. Treatment includes calcium supplements in a nasal spray or parenteral preparations. Salicylates and other nonsteroidal anti-inflammatory drugs (NSAIDs) may be used for pain control. Treatment may also include orthopedic surgery to replace a diseased hip or knee, or to decompress a narrowing of the spinal canal or nerve entrapment.

In severe forms of the condition, residuals may include slow and incomplete healing of fractures, a waddling or hobbling walk, and an increased susceptibility to pathologic fractures. There may be a collapse of the vertebra, osteosarcoma, and arthritis. Residuals may also include nerve palsies and hearing loss. It may be possible for the person to lead a normal life with self-administrated medications. However, if congestive heart failure (CHF) is present, the condition can be fatal.

• The disease must have become manifest to a degree of 10 percent or more within 1 year (for Hansen's disease (leprosy) and tuberculosis, within 3 years; multiple sclerosis, within 7 years) from the date of separation from service as specified in paragraph (a)(2) of this section. See 38 CFR 3.309 (a)  [chronic disease].

• The provisions for 10 and 20 percent evaluations for arthritis with multiple joint involvement without limitation of motion do not apply to these conditions as is reflected in Note (2) under DC 5003.

• May be entitled to special monthly compensation where the veteran has a single service-connected disability rated as 100% with additional service-connected disability or disabilities independently ratable at 60% or more, which are separate and distinct from the 100% service-connected disability and involves different anatomical segments or bodily systems. See  38 CFR 3.350(i)(1) – Special Monthly Compensation (SMC).

• Evaluate the diseases under diagnostic codes 5013 through 5024 as degenerative arthritis, based on limitation of motion of affected parts.