The clinical course of such lesions often extends for years, with deceptive and unexplained fluctuations. The important diagnostic procedure is contrast-enhanced MRI (Fig. 30-23). With dermoid cysts of the upper cervical region, as in the case reported by Adams and Wegner, complete and prolonged remissions from quadriparesis may occur.
Tumors of the foramen magnum, as mentioned, should be differentiated from spinal or brainstem- cerebellar multiple sclerosis, Chiari malformation with syrinx, and bony compression. Persistent occipital neuralgia with a foramen magnum syndrome is particularly suggestive of a tumor at that site. The early occipitonuchal pain must be differentiated from mundane cervical osteoarthritis. Treatment is surgical excision (Hakuba et al) followed by focused radiation if the resection is incomplete and the tumor is known to be radiosensitive.
In the past 50 years a group of neurologic disorders has been delineated that occur in patients with systemic neoplasia even though the nervous system is not the site of metastases or direct invasion or compression by the tumor. These so-called paraneoplastic disorders are not specific or confined to cancer, but the conditions are linked far more frequently than could be accounted for by chance. They assume special importance because in many cases the neurologic syndrome becomes apparent before the underlying tumor is found. The great variety of clinical presentations of paraneoplastic neurological disease can be appreciated from early series reported by Graus and colleagues of 200 patients: sensory neuropathy, 54 percent; cerebellar ataxia, 10 percent; limbic encephalitis, 9 percent; and others, including multiple sites, in 11 percent. Some of the paraneoplastic disorders that involve nerve and muscle—namely, polyneuropathy, polymyositis, and the myasthenic-myopathic syndrome of Lambert-Eaton—are described in later chapters on these subjects. Here we present the paraneoplastic processes that involve the spinal cord, cerebellum, brainstem, and cerebral hemispheres.
Comprehensive accounts of the paraneoplastic disorders may be found in the writings of Darnell and Posner, and Dalmau and Rosenfeld. Many are associated with immunoglobulin G (IgG) autoantibodies, but it should be remarked that although certain antibodies are associated with specific syndromes, they are not invariably linked to particular cancers and vice versa. Furthermore, the same syndromes and antibodies occur sometimes without an evident tumor, and in some cases multiple autoantibodies are present. This was emphasized in the survey by
Pittock and colleagues at the Mayo Clinic, who found that one-third of sera from patients with paraneoplastic neurologic disorders had more than one antibody. They have suggested that this reflects the numerous immunogenic onconeural proteins that are expressed by tumors. Consequently, the relationships between particular antibodies and a clinical syndromes listed in Table 30-6 should be taken as approximate, or nonexclusive. The presence of an autoantibody does not necessarily implicate a role in neuronal dysfunction and certain autoantibodies may be present in the serum of healthy individuals (see Dahm et al). Nonetheless, certain syndromes seem to occur disproportionately often with particular antibodies. Small cell cancer of the lung (see Gozzard et al), adenocarcinoma of the breast and ovary, thymoma (see Evoli and Lancaster), and Hodgkin disease are the tumors most often associated with these disorders, but the paraneoplastic neurologic syndromes occur in only a very small proportion of patients with these tumors.