FDG Uptake in Extramammary Paget's Disease on PET-CT
Yes, extramammary Paget's disease (EMPD) can show FDG uptake on PET-CT scans, though the pattern is variable and depends on tumor thickness and disease extent.
Primary Site FDG Uptake Patterns
EMPD demonstrates mild to moderate FDG uptake at primary cutaneous sites, particularly when tumors are thicker than 2 cm. 1 In a staging study of 7 EMPD patients, 4 showed mild FDG uptake at primary sites, and all 4 of these tumors were histologically confirmed to be thicker than 2 cm 1. This indicates that tumor thickness is a key determinant of metabolic activity on PET-CT.
- Primary EMPD lesions manifest as neoplastic skin thickening with FDG uptake at the affected anatomic site (perianal, vulvar, scrotal, or penile regions) 2
- The degree of uptake correlates with tumor burden and invasive depth 1
Metastatic Disease Detection
PET-CT is valuable for detecting metastatic spread in EMPD, showing hypermetabolic foci in lymph nodes and distant organs. 1, 2
- Among EMPD patients with FDG-avid primary tumors, PET-CT identified multiple hypermetabolic foci including skeletal metastases and lymph node involvement 1
- Metastatic EMPD demonstrates hypermetabolic inguinal, retroperitoneal, and mediastinal lymph nodes, as well as liver and bone metastases 2
- The sensitivity for detecting nodal and distant metastases makes PET-CT useful for staging advanced EMPD 2
Clinical Interpretation Caveats
Not all EMPD cases will show FDG uptake, particularly thin or superficial lesions, creating potential for false-negative scans. 1
- Thinner EMPD lesions (<2 cm) may not demonstrate significant FDG uptake, limiting PET-CT sensitivity for early-stage disease 1
- False-positive FDG uptake can occur from benign cutaneous and subcutaneous conditions including inflammation, infection, and post-procedural changes 3, 4
- Cutaneous malignancies including lymphoma, melanoma, and skin metastases can also show substantial FDG uptake, requiring histopathologic confirmation for definitive diagnosis 4
Practical Staging Approach
For suspected EMPD, perform PET-CT for staging when tumors are clinically thick (>2 cm) or when metastatic disease is suspected based on clinical examination or symptoms. 1, 2
- PET-CT is most useful for detecting occult metastases in patients with locally advanced primary tumors 1, 2
- Negative PET-CT does not exclude EMPD, particularly in thin lesions, and tissue diagnosis remains mandatory 1
- Positive FDG uptake in cutaneous lesions requires correlation with CT morphology and histopathologic confirmation, as benign inflammatory conditions can mimic malignancy 3, 5, 4