Cranial Nerves and Paraneoplastic Disorders

Cranial nerve (CN) and brainstem involvement is common in patients with paraneoplastic neurological syndromes. Paraneoplastic optic neuropathy (PON) is the most frequent cranial neuropathy and has been associated with small cell lung cancer (SCLC). Subacute sensorineural bilateral hearing loss is the most common cranial neuropathy in anti-Hu-related paraneoplastic neurologic syndrome. However, paraneoplastic CN involvement more frequently occurs in the context of a paraneoplastic brainstem encephalitis, probably due to damage of CN nuclei. Brainstem encephalitis may present as isolated syndrome or may be associated with a more widespread encephalomyelitis. Each part of the brainstem can be affected by the inflammatory process, but usually, depending on onconeuronal antibody specificity, different clinical features can be observed. The clinical characteristics of brainstem encephalitis are presented according to the type of antibody. Cancer immunotherapy, particularly immune checkpoint inhibitors, may also trigger cranial neuropathies that may be isolated or associated with other neurological manifestations.