Evaluation Components in Polyostotic Fibrous Dysplasia
Each component of the evaluation in polyostotic fibrous dysplasia is asked to assess disease extent, detect complications (particularly fractures and malignant transformation), identify associated endocrinopathies that worsen outcomes, and guide surgical planning—all of which directly impact morbidity, mortality, and quality of life.
Clinical History and Physical Examination
The clinical evaluation targets specific prognostic factors:
Age at symptom onset and fracture history: Peak fracture incidence occurs between 6-10 years of age, then decreases 1. Patients with metabolic abnormalities sustain their first fracture earlier (6.9 vs 16.6 years) and have higher lifetime fracture rates (0.29 vs 0.08 fractures/year) 1.
Pain assessment: Sudden onset pain may indicate pathologic fracture or malignant transformation, which occurs in <1% of cases but carries significant mortality risk 2, 3.
Endocrine symptoms: Identifying precocious puberty, hyperthyroidism, growth hormone excess, or Cushing syndrome is critical, as these endocrinopathies occur in McCune-Albright syndrome and are associated with earlier fractures and increased fracture frequency 1.
Neurological symptoms: Cranial nerve compression, ptosis, or spinal cord symptoms indicate craniospinal involvement requiring urgent surgical evaluation 4, 5.
Laboratory Testing
Phosphorus metabolism assessment is the single most important metabolic evaluation because phosphaturia is associated with both earlier age of first fracture (5.1 vs 16.6 years) and greater lifetime fracture rate (0.35 vs 0.08 fractures/year) 1.
Essential laboratory components include:
- Serum phosphate and 24-hour urinary phosphate: To detect phosphaturia, which predicts worse fracture outcomes 1
- Endocrine panel: Thyroid function, growth hormone/IGF-1, cortisol, and sex hormones to identify treatable endocrinopathies 1
- Alkaline phosphatase: Marker of bone turnover and disease activity
- Calcium and vitamin D: To optimize bone health and prevent secondary complications 6
Imaging Evaluation
Plain Radiography (Initial Assessment)
Plain films establish the diagnosis and document baseline skeletal involvement, showing characteristic ground-glass appearance, cortical thinning, bone expansion, and deformities 2, 4.
CT Scanning (Anatomic Detail)
CT is essential for:
- Craniofacial involvement: Demonstrates ground-glass appearance with well-defined borders, medullary widening, and cortical thinning 4
- Surgical planning: Provides precise anatomic detail for procedures, particularly in spine and rib involvement 5
- Detecting cystic/necrotic areas: These appear as low-density regions within affected bone 4
MRI (Soft Tissue and Marrow Assessment)
MRI complements CT by:
- Showing bone marrow involvement more clearly: Lesions appear hypointense on T1-weighted and hyperintense on T2-weighted sequences 4
- Detecting nerve compression: Combined CT and MRI evaluation most effectively identifies cranial and spinal nerve compression 4
- Assessing soft tissue extension: Critical for surgical planning and detecting complications 2
Nuclear Medicine Studies (Metabolic Activity)
18F-FDG PET/CT is the key modality for detecting malignant transformation, which is the most life-threatening complication:
- Heterogeneous FDG uptake corresponds to different metabolic stages of disease 7
- High FDG uptake guides biopsy to the most metabolically active areas 7
- Distinguishes active disease from quiescent lesions 3
- Whole-body assessment identifies all sites of involvement 7
99mTc-MDP bone scans show disease extent but have lower specificity for malignant transformation 3.
Bone Biopsy
Biopsy is indicated when:
- High FDG uptake suggests malignant transformation (osteosarcoma, fibrosarcoma, chondrosarcoma) 2, 7
- Atypical imaging features are present 2
- Diagnosis is uncertain despite imaging 7
PET/CT guides biopsy to the most metabolically active portion of lesions 7.
Functional Assessment
Document:
- Mobility limitations: Wheelchair use, assistive device requirements 8
- Pain interference with activities: Walking distance, ability to perform daily tasks 8
- Skeletal deformities: Particularly shepherd's crook deformity of proximal femur, which requires specific surgical intervention 9
Common Pitfalls to Avoid
Missing phosphaturia: This is the single metabolic abnormality most strongly associated with worse fracture outcomes and must be actively sought 1.
Relying solely on plain radiographs: Combined CT and MRI are necessary to fully assess craniospinal involvement and nerve compression 4.
Not obtaining PET/CT when malignant transformation is suspected: Increased pain, rapid growth, or atypical imaging features warrant metabolic imaging 2, 7, 3.
Delaying endocrine evaluation: Untreated endocrinopathies worsen fracture risk and should be identified early 1.
Inadequate long-term follow-up: Disease behavior changes over time, with peak fracture risk in childhood but potential for late complications including malignant transformation 1, 3.