What a Clinician Must Know Regarding Diagnosis of Paraneoplastic Neurological Syndromes

Paraneoplastic neurological syndromes (PNS) are rare, immune-mediated effects of a systemic cancer. PNS may affect the central and/ or peripheral nervous system. Most often, the neurological symptoms precede the cancer diagnosis. The clinician must be aware of the various PNS, as early acknowledgement of such syndromes facilitates early cancer diagnosis and might improve the prognosis. Onconeural antibodies are important diagnostic markers for PNS and approximately 50 % of the patients with PNS have antibodies. The PNS diagnosis is confirmed if such antibodies are present in the serum and/or spinal fluid. Supplementary investigations include MRI, EEG, and spinal fluid analysis, and these are often of diagnostic help for the diagnosis of limbic encephalitis or other paraneoplastic manifestations of the central nervous system. Neurophysiological tests are usually required to verify paraneoplastic neuropathy or neuronopathy. CT scans are used for cancer screening, but total body PDG-PET scan may be more sensitive in detecting small tumours. PDG-PET can also exhibit pathologic features in cases of limbic encephalitis, where MRI has not shown hypersignal. Other targeted investigations, such as ultrasound and various serological markers for cancer, may also be required to detect an underlying malignancy.