Recurrent 'Occult' 18F-FDG Uptake in an Atypical Case of Anti-Myeloperoxidase Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.

A 72-year-old woman, with anti-myeloperoxidase antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), presented with two episodes of spinal pachymeningitis (at two different levels 9 years apart, cervical in 2011 and dorso-lumbar in 2020) associated with aortitis and only demonstrated by F-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT). This association between aortitis and pachymeningitis in AAV appears exceptional. Moreover, the relapse of aortitis and pachymeningitis in 2020 was not accompanied by an increase in ANCA. This case demonstrates the value of 18F-FDG PET/CT in the management of AAV, providing evidence of the recurrence and distribution of lesions in various organs, including those with unexpected involvement. LEARNING POINTS: Involvement of large vessels such as the aorta is rarely associated with anti-myeloperoxidase antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), but has been described in a few cases. Possible aortic involvement should always be kept in mind while managing a patient with AAV.Pachymeningitis is rarely associated with AAV, but in case of unexplained and unspecific neurological symptoms in patients with AAV, such involvement should be considered.18F-FDG PET/CT is a promising tool for the management of patients with AAV, allowing unexpected sites, undetected by usual examinations, to be highlighted. In contrast to giant-cell arteritis, this exam has not, until now, been included in the recommended/systematic work-up of AAV.