Symptoms usually develop acutely or subacutely. The disease usually evolves over days, weeks, or at most a few months, and then stabilizes, with the patient neither improving nor worsening beyond that time. This differs from most degenerative diseases of the nervous system, which evolve over years and are inexorably progressive. In addition, the neurologic disorder is usually severe. Although subclinical peripheral neuropathies have been reported in a significant percentage of patients with cancer, most patients with peripheral or central nervous system paraneoplastic syndromes have disabling symptomatology.
Oligoclonal bands are common.
However, in many of the paraneoplastic syndromes, the pleocytosis present early in the evolution of the disease disappears after a few weeks to months. The IgG level usually remains elevated. Furthermore, certain disorders are characteristic of paraneoplastic syndromes. For example, approximately two thirds of patients suffering from LEMS have SCLC as the underlying cause. The diagnosis of a paraneoplastic syndrome is often inferential.