In simple words: Paget's disease of bone in the upper arm causes the bone to become bigger, weaker, and misshapen, making it easier to break. It's a long-term condition where the body doesn't replace old bone with new bone properly.

Osteitis deformans, also known as Paget’s disease of bone, affects the upper arm. It is a chronic metabolic bone disease characterized by abnormal bone remodeling, leading to enlarged, weakened, and deformed bones. The specific upper arm (right or left) is not specified in this code.

Example 1: A 65-year-old patient presents with pain and swelling in their upper arm. Imaging reveals bone enlargement and deformity characteristic of Paget's disease. The affected arm is not specified as right or left., A patient experiences a fracture in their upper arm after a minor fall. Subsequent examination and imaging suggest the underlying cause is Paget's disease of bone, but documentation doesn't specify the laterality of the affected arm., During a routine checkup, a patient's X-ray reveals bone changes indicative of Paget's disease in one of their upper arms. The patient is asymptomatic. No further details regarding right or left arm are recorded.

Documentation should include evidence of abnormal bone remodeling in the upper arm through imaging studies (X-ray, CT, MRI, bone scan), physical examination findings (bone enlargement, tenderness, deformity), and possibly laboratory tests (elevated alkaline phosphatase). Medical history and the absence of other conditions mimicking Paget's disease should also be documented. The lack of laterality specification should be explicitly noted.