[Pathogenesis of paraneoplastic neurological syndromes]

Paraneoplastic neurological syndromes (PNS) are thought to be caused by autoimmune processes triggered by the cancer and directed against antigens common to both the cancer and the nervous system. There are several clinical phenotypes in combinations with the neurological syndromes, origin of cancer and the specific autoantibodies. PNS with antibodies against channel receptors on the cell surface tend to respond favorably to antibody-depletion therapies; this suggests that the antibodies detected in these PNS groups are closely related to their pathogenesis. PNS having the antibodies against intracellular proteins might be caused by cytotoxic T cell-mediated cell death. This is because the following findings; 1) the prominent mononuclear cells in CSF, 2) the infiltration of inflammatory cells, mainly CD8+ T lymphocytes, in the tumor and the nervous tissue. In addition, T cell receptor usage of infiltrated T lymphocytes in the affected CNS lesions has been shown to be oligoclonal. We observed that the disease model could not be produced using only anti-intracellular antibodies such as anti-Yo or anti-Hu antibodies, but that CTL activity could be induced in CD8+ T cells isolated from the peripheral mononuclear cells obtained from PNS patients with anti-Yo or anti-Hu antibodies. The anti-Yo- or anti-Hu-antibody-positive patients possess common human leukocyte antigen (HLA) class I motifs. This implies that in patients with anti-Yo or anti-Hu antibodies, the presentation of the certain antigen peptides on the cell surface could be used to stimulate CD8+ T lymphocytes that could attack their target tissues as effectors. Antigen-specific CTL-mediated cell death has been observed in cancer immunology and PNS appears to be a potential candidates for a future CTL-mediated neurological disease model.

[Neuropathy associated with paraneoplastic neurological syndrome]

Paraneoplastic neurological syndromes (PNSs) are the remote effects of cancer on the nervous system. The peripheral nervous system is an important targets of PNS. The neuropathies associated with PNS are reviewed in this article. Among the various paraneoplastic neuropathies, the main classical syndorome of PNS is subacute sensory neuronopathy that involves the cell bodies of sensory neurons in the dorsal root ganglia. Its clinical symptoms include sensory ataxia. Onconeuronal antibodies such as anti-Hu and anti-CV2/CRMP5 antibodies are frequently associated with this syndrome. In contrast to this classical form of PNS, non-classical syndromes are considered as heterogeneous neuropathies. The clinical features of non-classical syndromes are variable and no evident association between a clinical phenotype and onconeuronal antibodies has been established. Early detection and treatment of cancer is an essential for management of PNS. Neuropathies with paraproteinemia are also important clinical entities of PNS. IgM M-protein is most likely to cause neuropathy. Patients with IgM paraproteinemic neuropathy is usually characterized by predominan distal and sensory impairment, prolonged distal motor latencies in nerve conduction studies, and the presence of anti-MAG and SGPG antibodies.

[Paraneoplastic neurological syndrome--definition and history]

Paraneoplastic neurological syndrome (PNS) may affect any part of the nervous system and muscles. PNS is a rare disorder caused by the remote effects of cancer and is considered to be immune-mediated. Since the 1980s, several specific onco-neural antibodies and T-cell responses against onco-neural molecules have been reported, as shown in the historical review in this article. Immunoresponses to cancer are considered to cross-react with self-antigens in the nervous system or muscle. The presence of such onco-neural antibodies is a useful diagnostic marker for PNS and occult cancer. Despite sustained efforts to elucidate the effects of such antibodies on neuron, only a few onco-neural antibodies have been identified as primary effectors of neurological symptoms. However the absence of these antibodies does not exclude a PNS. In some instances, these antibodies can be detected in cancer patients without PNS. PNS diagnosis requires excluding many other complications of cancer and mimics of other neurological diseases as differential diagnoses. Recently, an international panel of experts provided useful diagnostic criteria for PNS. These criteria are based on well-characterized onco-neural antibodies and specific neurological syndromes. Probable cases of PNS are strongly advised to undergo early antitumor therapy and immunotherapy to prevent progressive neuronal death. As the symptoms of PNS often appear before the diagnosis of malignant cancer, repeated searches for occult cancer are recommended, if the tumor has not yet been found. Further studies are required to clarify the exact mechanisms underlying neuronal damage in PNS, which may lead to the development of more rational therapies and greater understanding of immunology in the nervous system.

Antibody to CCDC104 is associated with a paraneoplastic antibody to CDR2 (anti-Yo)

Patients with cancer may develop paraneoplastic neurological syndromes (PNS) in which onconeural antibodies are important diagnostic findings. As the functional role of onconeural antibodies is largely unknown, insight gained by identifying associated antibodies may help to clarify the pathogenesis of the PNS. In this study, we identified patients with Yo antibodies who also had antibodies to an uncharacterized protein called coiled-coil domain-containing protein 104 (CCDC104). We found a significant association between CCDC104 and Yo antibodies (4 of 38, 10.5%), but not other onconeural antibodies (0 of 158) (P = 0.007, Fisher's exact test). The prevalence of CCDC104 antibodies was approximately similar in patients with cancer (8 of 756, 1.1%) and in healthy blood donors (2 of 300, 0.7%). CCDC104 antibodies were not associated with PNS, as this was found in only two of the ten CCDC104-positive patients. The CCDC104 protein, whose function is unknown, is expressed in various human tissues, including the brain, and is localized mainly to the nucleus, but is also found in the cytoplasm. The association between Yo and CCDC104 antibodies may indicate functional similarities.

Expression of various glutamate receptors including N-methyl-D-aspartate receptor (NMDAR) in an ovarian teratoma removed from a young woman with anti-NMDAR encephalitis

A 21-year-old woman developed psychiatric symptoms, progressive unresponsiveness, generalized seizures, severe dyskinesia, marked fluctuation of blood pressure, and hypersalivation after a flu-like episode. Anti-glutamate receptor (GluR)ε2 and anti-N-methyl-D-aspartate receptor (NMDAR) antibodies were positive in both her serum and CSF. After she recovered five months later she underwent surgery to remove a right ovarian teratoma. Immunohistochemical examinations of her teratoma disclosed abundant expression of various GluRs including NR2B subunit of NMDAR, GluR1, and GluR2/3. These immunoreactivities of GluRs were seen not only in small areas of neural tissue identified as anti-glial fibrillary acidic protein (GFAP)-immunoreactive areas but also in other large areas of undifferentiated neuroepithelial tissue without GFAP immunoreactivity. Our findings strongly support the recent idea that neural elements in ovarian teratoma play an important role in the production of antibodies to NMDARs in anti-NMDAR encephalitis. Additionally, the study of control ovaries clearly showed NR2B-related immunoreactivity in the cytoplasm of oocytes, indicating that the normal ovary itself has expression of NMDARs. This finding might provide a clue to understand the pathogenesis of this disease in female patients without ovarian teratoma.

Antibodies to the GABA(B) receptor in limbic encephalitis with seizures: case series and characterisation of the antigen

BACKGROUND

Some encephalitides or seizure disorders once thought idiopathic now seem to be immune mediated. We aimed to describe the clinical features of one such disorder and to identify the autoantigen involved.

METHODS

15 patients who were suspected to have paraneoplastic or immune-mediated limbic encephalitis were clinically assessed. Confocal microscopy, immunoprecipitation, and mass spectrometry were used to characterise the autoantigen. An assay of HEK293 cells transfected with rodent GABA(B1) or GABA(B2) receptor subunits was used as a serological test. 91 patients with encephalitis suspected to be paraneoplastic or immune mediated and 13 individuals with syndromes associated with antibodies to glutamic acid decarboxylase 65 were used as controls.

FINDINGS

All patients presented with early or prominent seizures; other symptoms, MRI, and electroencephalography findings were consistent with predominant limbic dysfunction. All patients had antibodies (mainly IgG1) against a neuronal cell-surface antigen; in three patients antibodies were detected only in CSF. Immunoprecipitation and mass spectrometry showed that the antibodies recognise the B1 subunit of the GABA(B) receptor, an inhibitory receptor that has been associated with seizures and memory dysfunction when disrupted. Confocal microscopy showed colocalisation of the antibody with GABA(B) receptors. Seven of 15 patients had tumours, five of which were small-cell lung cancer, and seven patients had non-neuronal autoantibodies. Although nine of ten patients who received immunotherapy and cancer treatment (when a tumour was found) showed neurological improvement, none of the four patients who were not similarly treated improved (p=0.005). Low levels of GABA(B1) receptor antibodies were identified in two of 104 controls (p<0.0001).

INTERPRETATION

GABA(B) receptor autoimmune encephalitis is a potentially treatable disorder characterised by seizures and, in some patients, associated with small-cell lung cancer and with other autoantibodies.

FUNDING

National Institutes of Health.

Paraneoplastic antibody during follow-up of a patient with anti-Ri-associated paraneoplastic neurological syndrome

BACKGROUND

The role of classical antineuronal antibody determinations to confirm the paraneoplastic aetiology of a neurological syndrome is well established. However, the value of antineuronal antibody estimation during follow-up of paraneoplastic neurological syndromes (PNS) is not known.

AIMS OF THE STUDY

Prospective analysis of antibody concentrations in follow-up serum samples from a patient with anti-Ri-associated PNS.

METHODS

Semiquantitative estimation of antibody concentrations with an ELISA using recombinant Ri antigen.

RESULTS

Semiquantitative estimation of circulating anti-Ri antibodies demonstrated a renewed increase in antibody levels preceding relapse of the cancer, as confirmed using F-fluorodeoxyglucose positron emission tomography (FDG-PET).

CONCLUSIONS

This is the first prospective report on serial anti-Ri antibody determinations. As a large increase in antineuronal antibody concentrations in follow-up serum samples preceded relapse of the cancer, paraneoplastic antineuronal antibodies may represent a marker for tumour activity in this case. These results warrant further multicentre studies to investigate the ability of serial quantification of classical antineuronal antibodies in monitoring PNS and in predicting relapse of cancers.

Autonomic ganglia, acetylcholine receptor antibodies, and autoimmune ganglionopathy

Nicotinic acetylcholine receptors (AChR) are ligand-gated cation channels that are present throughout the nervous system. The ganglionic (alpha3-type) neuronal AChR mediates fast synaptic transmission in sympathetic, parasympathetic and enteric autonomic ganglia. Autonomic ganglia are an important site of neural integration and regulation of autonomic reflexes. Impaired cholinergic ganglionic synaptic transmission is one important cause of autonomic failure. Ganglionic AChR antibodies are found in many patients with autoimmune autonomic ganglionopathy (AAG). These antibodies recognize the alpha3 subunit of the ganglionic AChR, and thus do not bind non-specifically to other nicotinic AChR. Patients with high levels of ganglionic AChR antibodies typically present with rapid onset of severe autonomic failure, with orthostatic hypotension, gastrointestinal dysmotility, anhidrosis, bladder dysfunction and sicca symptoms. Impaired pupillary light reflex is often seen. Like myasthenia gravis, AAG is an antibody-mediated neurological disorder. Antibodies from patients with AAG inhibit ganglionic AChR currents and impair transmission in autonomic ganglia. An animal model of AAG in the rabbit recapitulates the important clinical features of the human disease and provides additional evidence that AAG is an antibody-mediated disorder caused by impairment of synaptic transmission in autonomic ganglia.

Paraneoplastic chronic demyelinating neuropathy and Lambert-Eaton myasthenic syndrome associated with multiple anti-neural antibodies and small-cell lung cancer

Lambert-Eaton myasthenic syndrome (LEMS) developed in a patient with presumed chronic inflammatory demyelinating polyneuropathy (CIDP) and negative chest CT. Since antibodies against both Hu and voltage-gated calcium channel (VGCC) were detected, repeated chest CT was performed, which eventually showed a pulmonary mass lesion. Biopsy revealed small cell lung cancer (SCLC) indicating the importance of repeated chest CT in LEMS even when an existing autoimmune-like disease and negative CT may suggest an autoimmune origin. This is the first report of paraneoplastic CIDP and LEMS associated with anti-Hu, anti-VGCC and SCLC.

Neurological response to early removal of ovarian teratoma in anti-NMDAR encephalitis

We report an 18-year-old woman with anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, who developed psychiatric symptoms, progressive unresponsiveness, dyskinesias, hypoventilation, hypersalivation and seizures. Early removal of an ovarian teratoma followed by plasma exchange and corticosteroids resulted in a prompt neurological response and eventual full recovery. Serial analysis of antibodies to NR1/NR2B heteromers of the NMDAR showed an early decrease of serum titres, although the cerebrospinal fluid titres correlated better with clinical outcome. The patients' antibodies reacted with areas of the tumour that contained NMDAR-expressing tissue. Search for and removal of a teratoma should be promptly considered after the diagnosis of anti-NMDAR encephalitis.