MRI and CSF studies are important to rule out neurologic complications due to direct spread of cancer. In most PNDs the MRI findings are nonspecific. CSF findings typically consist of mild to moderate pleocytosis (<200 mononuclear cells, predominantly lymphocytes), an increase in the protein concentration, and a variable presence of oligoclonal bands.

• Paraneoplastic encephalomyelitis and focal encephalitis describe an inflammatory process with multifocal involvement of the nervous system. Clinical manifestations depend on area involved, and syndromes may occur alone or in combination.
• Cortical encephalitis, which may present as “epilepsia partialis continua.”
• Limbic encephalitis, characterized by confusion, depression, agitation, anxiety, severe short-term memory deficits, partial complex seizures, and sometimes dementia (the MRI usually shows unilateral or bilateral medial temporal lobe abnormalities).
• Brainstem encephalitis presents with eye movement disorders (nystagmus, opsoclonus, supranuclear or nuclear paresis), cranial nerve paresis, dysarthria, dysphagia, and central autonomic dysfunction.
• Opsoclonus-myoclonus syndrome consists of involuntary, chaotic eye movements in all directions of gaze plus myoclonus; it is frequently associated with ataxia.
• Paraneoplastic cerebellar degeneration begins as dizziness, oscillopsia, blurry or double vision, nausea, and vomiting; a few days or weeks later, dysarthria, gait and limb ataxia, and variable dysphagia can appear.
• Myelitis, which may cause lower or upper motor neuron symptoms, myoclonus, muscle rigidity, and spasms.
• Autonomic dysfunction occurs as a result of involvement of the neuraxis at multiple levels, including hypothalamus, brainstem, and autonomic nerves. Cardiac arrhythmias, postural hypotension, and central hypoventilation are frequent causes of death.
• Encephalitis with antibodies to cell-surface or synaptic proteins can occur without tumor association and may occur predominantly in children or young adults. An example is N-methyl-D-aspartate (NMDA) receptor autoantibodies that present as a virus-like syndrome followed by a prominent psychiatric disturbance with involuntary movements; in young women, ovarian teratomas are frequently present. Despite dramatic severity at times, patients usually respond to treatment of the tumor (if found) and immunotherapy.
• Cancer-associated retinopathies involve cone and rod dysfunction with photosensitivity, progressive loss of vision and color perception, central or ring scotomas, night blindness, and attenuation of photopic and scotopic responses in the electroretinogram (ERG).
• Dorsal root ganglionopathy (sensory neuronopathy) is characterized by sensory deficits that may be symmetric or asymmetric, painful dysesthesias, radicular pain, and decreased or absent reflexes; all modalities of sensation can be involved.