What is the diagnostic approach for Paget's (Osteitis Deformans) disease?

Diagnosis of Paget's Disease of Bone (Osteitis Deformans)

Paget's disease of bone is diagnosed through a combination of elevated serum alkaline phosphatase, characteristic radiographic findings on plain films, and radionuclide bone scanning to assess disease extent. 1, 2

Clinical Presentation

Most cases are discovered incidentally rather than through symptoms 1, 3:

• Asymptomatic detection occurs via incidental finding of elevated alkaline phosphatase on routine labs or abnormal radiographs in patients over 55 years 1, 3
• Symptomatic presentations include bone pain, bone enlargement with increased warmth over affected areas, pathologic fractures, secondary arthritis, and compression neuropathy 1, 3

Laboratory Evaluation

Serum total alkaline phosphatase (ALP) is the recommended first-line biochemical screening test, measured in combination with liver function tests 2:

• Elevated ALP reflects increased osteoblastic activity in active disease 4
• More specific bone formation markers can be used: PINP (intact N-terminal type 1 procollagen propeptide) or CTX (cross-linked C-telopeptide) 4
• Routine measurement should include alkaline phosphatase, calcium, 25-hydroxy-vitamin D, phosphate, and parathyroid hormone levels to exclude other metabolic bone diseases 5

Imaging Studies

Plain Radiographs (First-Line)

Plain radiographs of clinically or biochemically suspicious skeletal regions are the initial imaging modality of choice 4, 2:

• Characteristic findings include trabecular and cortical thickening, bone enlargement, and areas of sclerosis in late disease 6
• Lytic phase shows osteolysis, particularly osteoporosis circumscripta in the skull and subchondral involvement in long bones 6
• Mixed phase demonstrates repair superimposed on resorption with trabecular thickening 6
• Blastic phase shows predominant sclerosis 6

Radionuclide Bone Scan (Essential for Disease Mapping)

Radionuclide bone scans, in addition to targeted radiographs, are recommended to fully and accurately define the extent of metabolically active disease 2:

• Bone scintigraphy demonstrates marked increased uptake in all phases of Paget's disease 6
• This imaging is critical for identifying polyostotic involvement that may not be clinically apparent 2

Advanced Imaging (Selective Use)

• CT and MRI show changes similar to plain radiographs in uncomplicated disease with maintenance of yellow marrow 6
• These modalities are particularly useful when evaluating for complications such as sarcomatous transformation 6

Common Sites of Involvement

The disease most frequently affects 6:

• Skull (25%-65% of cases)
• Spine (30%-75%)
• Pelvis (30%-75%)
• Proximal long bones (25%-30%)

Key Diagnostic Pitfalls to Avoid

• Do not rely solely on symptoms: Most patients are asymptomatic, and the disease is typically discovered incidentally 1, 3
• Do not skip bone scanning: Plain radiographs alone may miss additional sites of involvement that could influence management 2
• Ensure vitamin D and calcium sufficiency: Check these levels as part of the initial workup, as deficiency must be corrected before bisphosphonate treatment to prevent hypocalcemia 3
• Rule out malignant transformation: Sarcomatous transformation occurs in approximately 1% of cases and appears as focal bone destruction extending through cortex with soft-tissue mass 6