¹⁸F FDG PET/CT in a Rare Case of Erdheim–Chester Disease with Extensive Cutaneous and Skeletal Involvement

A 41-year-old male presented with rapidly progressing extensive nodular skin lesions. Skin biopsy was suggestive of histiocytic disease with fibrosis and BRAF-V600E mutation. ¹⁸F fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F FDG PET/CT) was done to assess disease extent [Figure 1a] FDG PET/CT maximum intensity projection image demonstrates extensive patchy areas of FDG uptake in the skin and in the marrow and bones [Figure 1b and c]. Demonstrates multiple nodular soft-tissue thickening along cutaneous and subcutaneous planes in the bilateral mammary region, upper trunk, and in bilateral arms [Figure 1d and e]. Demonstrates lesions in predominantly in the marrow of bilateral distal tibia and in multiple small bones of bilateral feet [Figure 1f and g]. Demonstrates FDG avid subtle sclerotic lesion in the left iliac bone. Scan findings were suggestive of extensive skeletal, marrow, and skin involvement [Figure 1h and i]. Demonstrates skin biopsy showing circumscribed nodular proliferation of polygonal, epithelioid to spindle cells with moderate to abundant pale vacuolated cytoplasm without atypia and presence of Touton giant cells and eosinophils. The usual initial clinical presentation in Erdheim–Chester disease (ECD) is related to skeletal involvement,[1] however, despite such extensive involvement as demonstrated by PET/CT, the patient was asymptomatic for skeletal disease. The usual extraskeletal sites of involvement are the cardiovascular system and retroperitoneal organs.[23] Skin involvement in ECD is rather uncommon. To our knowledge, there are not many case reports on FDG PET/CT in ECD showing such extensive cutaneous involvement. To add, FDG PET/CT has a significant role in diagnosis, assessing the disease extent, and treatment response and also acts as a potential biomarker of BRAF mutation.[4]

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Figure 1 41 yr old male with biopsy proven histiocytic disease with fibrosis, referred for ¹⁸F-fluorodeoxyglucose positron emission tomography–computed tomography (¹⁸F-FDG PET/CT) to assess disease extent. (a) FDG PET/CT MIP image and transaxial and coronal images (b-g) demonstrates FDG avid cutaneous, marrow and sclerotic skeletal lesions highlighted by red arrows-suggestive of extensive skeletal, marrow and skin involvement. Skin biopsy (h) and (i) showing circumscribed nodular proliferation of polygonal, epithelioid to spindle cells and presence of touton giant cells and eosinophils

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