An Atypical Case of Vasculitis: When ‘Occult’ 18FDG-PET Scan Findings Create a Classification Dilemma

We describe a 66-year old patient with a recurrent ulcer on her right ankle. Biopsy revealed medium-vessel vasculitis consistent with cutaneous polyarteritis nodosa. There were no signs or symptoms suggestive of systemic vasculitis, but a 18FDG-PET scan showed areas of increased uptake around the large arteries and the pelvic and shoulder girdles. These findings suggested polymyalgia rheumatica in the setting of large-vessel vasculitis. This case thus supports the statement from the Chapel-Hill consensus conference that classification of systemic vasculitis by vessel size is based on the vessels predominantly involved, but vessels of other sizes may also be affected. LEARNING POINTS: The classification of vasculitis needs further refinement as some patients may not easily fit into just one category. Conditions that include aspects of different vasculitis also exist and cannot be classified using the Chapel Hill nomenclature. The role of PET scan in the assessment of PAN needs further evaluation.