Immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized contemporary oncology, presenting efficacy in various solid tumors and lymphomas. However, ICIs may potentially overstimulate the immune system, leading to immune-related adverse events (irAEs). IrAEs may affect multiple organs, such as the colon, stomach, small intestine, kidneys, skin, lungs, joints, liver, lymph nodes, bone marrow, brain, heart, and endocrine glands (e.g., pancreas, thyroid, or adrenal glands), exhibiting autoimmune inflammation. ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) is commonly used in oncology for staging and assessment of therapy responses, but it may also serve as a tool for detecting irAEs. This review aims to present various patterns of metabolic activation associated with irAEs due to ICI treatment, identifiable through ¹⁸F-FDG PET/CT. It describes the advantages of early detection of irAEs, but also presents the challenges in differentiating them from tumor progression. It also delves into aspects of molecular response assessment within the context of pseudoprogression and hyperprogression, along with typical imaging findings related to these phenomena. Lastly, it summarizes the role of functional PET imaging in oncological immunotherapy, speculating on its future significance and limitations.

Granulomatosis with polyangiitis (GPA) is a vasculitis affecting small and medium-sized blood vessels. It typically presents with upper respiratory tract, lung, and kidney involvement. However, the disease may involve multiple other organs, and not all cases present with these classic mani­festations. Periocular lesions are described in the GPA and, especially in the case of isolated, single-site disease, require extensive differentiation from other diseases, such as IgG4-related disease or myofibroblastic tumor. However, periocular lesions and coexisting symptoms suggesting changes in the central nervous system without other organ changes are undoubtedly a diagnostic challenge. Such situations are described in the literature mainly as case reports, not as a rule in connection with GPA. The impetus for writing this article and analyzing the literature was a case of GPA manifesting as infiltration of the skull base presenting as multiple cranial nerve palsies. A review of atypical cases of GPA in the literature suggests that skull-based involvement is an important yet easily overlooked presentation. Through this case-based review, we aim to raise awareness that GPA may present with isolated cranial nerve palsies.