In children, this syndrome is usually a manifestation of neuroblastoma, but it is more common and occurs in adults in relation to breast cancer and small cell lung cancer. The unique feature of the neuroblastoma is a response of this syndrome to corticosteroids and ACTH in most children and in some adults, and resolution of the neurologic signs when the neuroblastoma is removed. A subgroup of breast cancers produce an antineuronal antibody directed against a different RNA-binding antigen from the anti-Hu antibody; thus it has been termed “anti-Ri” (antineuronal antibody type 2 (ANNA 2)). This antibody is not found in the opsoclonus–ataxic syndrome of neuroblastoma and is present only rarely with small cell lung cancer. More commonly present in patients with small cell lung cancer are glycine receptor autoantibodies, though these antibodies are also found in patients without opsoclonus-myoclonus (see Armangué et al). There have also been a limited number of positive serologic tests in children with opsoclonus, apparently without an underlying tumor. A few such patients have had a mild pleocytosis in the CSF; the MRI is usually normal. More complex syndromes have been reported with the anti-Ri antibody, manifest by rigidity and intense stimulus-sensitive myoclonus in addition to the core features of opsoclonus and ataxia.
The neuropathologic findings have not been distinctive; mild cell loss has been described in the Purkinje cell layer, inferior olives, and brainstem, with mild inflammatory changes (Luque et al).
Besides in association with breast cancer, we have observed the opsoclonus–myoclonus syndrome in a middle-aged woman with bronchial carcinoma and in a man with gastric carcinoma. Similar cases occur with both cerebellar ataxia and an irregular tremor, which we have interpreted as myoclonic in character. These patients were found to have marked degeneration of the dentate nuclei. The prognosis in this syndrome is somewhat better than that for the other paraneoplastic diseases, but besides a trial of steroids, plasma exchange, or intravenous immunoglobulin, there is little that can be done but search for the tumor and resect it if possible.
In addition to subacute degeneration of spinal cord tracts that may be associated with paraneoplastic cerebellar degeneration (see earlier), there has been described a rapidly progressive form of more widespread degeneration of the spinal cord (Mancall and Rosales). The myelopathy is characterized by a rapidly ascending sensorimotor deficit that terminates fatally in a matter of weeks. There is a roughly symmetrical necrosis of both the gray and white matter of most of the cord. This necrotizing myelopathy is distinctly rare, being far less common than compression of the spinal cord from cancer and even less frequent than intramedullary spinal cord metastases. Flanagan and colleagues have summarized a large series of their cases and described a variety of presentations including longitudinally extensive involvement on imaging studies that simulate the pattern seen with anti-aquaporin antibodies of Devic disease as described in Chaps. 35 and 42. It can, therefore, be said that there is a paraneoplastic type of neuromyelitis optica. Most of their cases had a CSF pleocytosis, half had oligoclonal bands, and one of the known paraneoplastic autoantibodies was found in the majority.