Reduction of P/Q-type calcium channels in the postmortem cerebellum of paraneoplastic cerebellar degeneration with Lambert-Eaton myasthenic syndrome

Neuronal autoantigens--pathogenesis, associated disorders and antibody testing

The discovery of disorders that are associated with antibodies to neuronal cell-surface proteins has led to a paradigm shift in our understanding of CNS autoimmunity. These disorders can occur in patients with or without cancer-often children or young adults who develop psychosis, catatonic or autistic features, memory problems, abnormal movements, or seizures that were previously considered idiopathic. The autoantigens in such cases have crucial roles in synaptic transmission, plasticity and peripheral nerve excitability. Patients can be comatose or encephalopathic for months and yet fully recover with supportive care and immunotherapy. By contrast, disorders in which the antibodies target intracellular antigens, and in which T-cell-mediated irreversible neuronal degeneration occurs, show a considerably poorer response to treatment. In this article, we review the various targets of neuronal antibodies, focusing predominantly on autoantigens located on the cell surface or synapses-namely, N-methyl-D-aspartate receptors, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, γ-aminobutyric acid receptors, leucine-rich glioma-inactivated protein 1, contactin-associated protein-like 2, and metabotropic glutamate receptors. We also provide an algorithm to identify and assess antibodies that bind to cell-surface and synaptic antigens.

Central nervous system neuronal surface antibody associated syndromes: review and guidelines for recognition

The concept of antibody mediated CNS disorders is relatively recent. The classical CNS paraneoplastic neurological syndromes are thought to be T cell mediated, and the onconeural antibodies merely biomarkers for the presence of the tumour. Thus it was thought that antibodies rarely, if ever, cause CNS disease. Over the past 10 years, identification of autoimmune forms of encephalitis with antibodies against neuronal surface antigens, particularly the voltage gated potassium channel complex proteins or the glutamate N-methyl-D-aspartate receptor, have shown that CNS disorders, often without associated tumours, can be antibody mediated and benefit from immunomodulatory therapies. The clinical spectrum of these diseases is not yet fully explored, there may be others yet to be discovered and some types of more common disorders (eg, epilepsy or psychosis) may prove to have an autoimmune basis. Here, the known conditions associated with neuronal surface antibodies are briefly reviewed, some general aspects of these syndromes are considered and guidelines that could help in the recognition of further disorders are suggested.

Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular autoimmune disease that has served as a model for autoimmunity and tumour immunology. In LEMS, the characteristic muscle weakness is thought to be caused by pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Half of patients with LEMS have an associated tumour, small-cell lung carcinoma (SCLC), which also expresses functional VGCC. Knowledge of this association led to the discovery of a wide range of paraneoplastic and non-tumour-related neurological disorders of the peripheral and central nervous systems. Detailed clinical studies have improved our diagnostic skills and knowledge of the pathophysiological mechanisms and association of LEMS with SCLC, and have helped with the development of a protocol for early tumour detection.

Neuromuscular complications

Although direct neoplastic involvement of muscle tis-sue is surprisingly rare, considering the large amount of body mass that is represented by muscle tissue, the most important and unresolved muscle effect is muscle cachexia.Other associations, such as inflammatory, paraneo-plastic, toxic, and several extremely rare associations,have been described. Drug-induced toxicity and radiation recall syndrome need to be taken into consideration when muscle symptoms appear in patients with cancer.

Paraneoplastic cerebellar degeneration

One of the most dramatic and devastating examples of a remote effect of cancer is paraneoplastic cerebellar degeneration (PCD). There is convincing evidence that this disorder is caused by autoimmunity directed against cerebellar targets. Typically, the neurological presentation antedates the diagnosis of malignancy, and the cancer, when found, tends to be localized and responsive to treatment. Diagnosis depends on clinical suspicion, serology for paraneoplastic antibodies, and a focused search for cancer. Neuronal autoantibody tests facilitate the diagnosis and help direct the search for malignancy. Unfortunately, even with prompt diagnosis, current treatment strategies meet with limited success. Optimum management includes early diagnosis, treatment of cancer to remission, immunosuppression, symptomatic therapies, and compassionate support.

VGCC antibody-positive paraneoplastic cerebellar degeneration presenting with positioning vertigo

A 70-year-old woman developed paraneoplastic cerebellar degeneration (PCD) due to P/Q-type and N-type voltage-gated calcium channel antibodies and small cell lung cancer, the main clinical manifestations of which were severe positioning vertigo and vomiting. Loss of the visual suppression of caloric nystagmus, spontaneous downbeat nystagmus, periodic alternating nystagmus, and positioning vertigo in our patient most probably corresponds to the cerebellar flocculus/paraflocculus lesion caused by PCD.

Selective loss of Purkinje cells in a patient with anti-gliadin-antibody-positive autoimmune cerebellar ataxia

The patient was an 84-year-old woman who had the onset of truncal ataxia at age 77 and a history of Basedow's disease. Her ataxic gait gradually deteriorated. She could not walk without support at age 81 and she was admitted to our hospital at age 83. Gaze-evoked nystagmus and dysarthria were observed. Mild ataxia was observed in all limbs. Her deep tendon reflex and sense of position were normal. IgA anti-gliadin antibody, IgG anti-gliadin antibody, anti-SS-A/Ro antibody, anti-SS-B/La antibody and anti-TPO antibody were positive. A conventional brain MRI did not show obvious cerebellar atrophy. However, MRI voxel based morphometry (VBM) and SPECT-eZIS revealed cortical cerebellar atrophy and reduced cerebellar blood flow. IVIg treatment was performed and was moderately effective. After her death at age 85, the patient was autopsied. Neuropathological findings were as follows: selective loss of Purkinje cells; no apparent degenerative change in the efferent pathways, such as the dentate nuclei or vestibular nuclei; no prominent inflammatory reaction. From these findings, we diagnosed this case as autoimmune cerebellar atrophy associated with gluten ataxia. All 3 autopsies previously reported on gluten ataxia have noted infiltration of inflammatory cells in the cerebellum.

In this case, we postulated that the infiltration of inflammatory cells was not found because the patient's condition was based on humoral immunity. The clinical conditions of gluten ataxia have not yet been properly elucidated, but are expected to be revealed as the number of autopsied cases increases.

Update on paraneoplastic neurological syndromes

PURPOSE OF REVIEW

To describe specificities and new advances in treatment of paraneoplastic neurological syndromes (PNS).

RECENT FINDINGS

PNS are defined as neurological syndromes of unknown cause that often antedate the diagnosis of an underlying cancer that is usually not clinically evident. The clinical signs of PNS are accurately described and 'classical' PNS have been established. Within the context of these syndromes, the concept of limbic encephalitis has evolved dramatically in the last 2 years due to the description of new auto-antibodies. The diagnosis and treatment of the associated cancer remains the key goal of the clinical management of PNS. However, the specific treatment of the neurological symptoms primarily depends on the immunological findings.

SUMMARY

There is increasing recognition of an extensive array of PNS and of several paraneoplastic antibodies as biological markers of these disorders. Basic immunological studies support the pathogenic role of some of these antibodies. Others are only markers of the disease.

Favorable response to rituximab in a patient with anti-VGCC-positive Lambert-Eaton myasthenic syndrome and cerebellar dysfunction

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease that is characterized by impaired transmission across the neuromuscular junction due to autoantibodies directed against the presynaptic voltage-gated calcium channels (VGCC-ab). Clinical symptoms are usually characterized by proximal muscle weakness and mild dysautonomia. In some patients there are signs of cerebellar dysfunction as well, usually associated with cancer. Here we report the long-term follow-up of a patient with VGCC-ab-positive LEMS and a severe cerebellar syndrome but without evidence of cancer over 5 years. While conventional immunosuppressive therapy (steroids, azathioprine) failed, he improved with plasma exchange and consecutive treatment with rituximab. Muscle Nerve 40: 305-308, 2009.

Lambert-Eaton myasthenic syndrome: search for alternative autoimmune targets and possible compensatory mechanisms based on presynaptic calcium homeostasis

The Lambert-Eaton myasthenic syndrome (LEMS) is a disease of neuromuscular transmission in which autoantibodies against the P/Q-type voltage-gated calcium channel (VGCC) at the presynaptic nerve terminal play a major role in decreasing quantal release of acetylcholine (ACh), resulting in skeletal muscle weakness and autonomic symptoms. It is associated with cancer, particularly small-cell lung carcinoma (SCLC), in 50-60% of LEMS patients; the nerve terminal and carcinoma cells apparently share a common antigen (VGCC), suggesting an immunological cross-reactivity that may lead to the neurological abnormality. Non-tumor LEMS has a strong association with HLA-DR3-B8. In approximately 15% of LEMS patients, no anti-P/Q-type VGCC antibodies are found, suggesting recognition of other targets(s). The VGCC-associated protein synaptotagmin could be one candidate, because it acts as an exocytotic calcium receptor, is implicated in fast ACh release; its N-terminus is exposed extracellularly during exocytosis and it is expressed in SCLC. Antibodies against synaptotagmin-1 were detected in both anti-VGCC-positive and -negative LEMS patients (20%), and it can be immunogenic, allowing induction of an animal model of LEMS. Another candidate target is the M1-type presynaptic muscarinic ACh receptor (M1 mAChR), also expressed extracellularly on motor nerve terminals; it modulates cholinergic transmission, linking to P/Q-type VGCC. In our series of 25 LEMS patients with and without SCLC, anti-M1 mAChR antibodies were prevalent in both anti-VGCC-positive and -negative LEMS patients. Autonomic symptoms seemed more frequent in the latter; serum from one of them passively transferred LEMS-type electrophysiological defects to mice. As a compensatory mechanism, researchers in Oxford suggested a shift in the dependence of ACh release from the P/Q-type to other types of VGCC. We have also focused on G protein-coupled mAChRs and neurotrophins, which may affect both P/Q-type VGCC and clathrin-independent "kiss-and-run" synaptic vesicle recycling (fast-mode of endocytosis) via protein kinase C activation. We hypothesize that these signaling cascades help to compensate for the immune-mediated defects in calcium entry in LEMS, compensation that may frequently be restricted by the coincident anti-M1 mAChR antibodies in this disease.

Cerebellar ataxia in non-paraneoplastic Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an immune-mediated disorder of the neuromuscular junction that rarely is associated with cerebellar ataxia (CA). We describe two patients with non-paraneoplastic LEMS associated with CA who showed high levels of anti-P/Q-type voltage-gated calcium channels antibodies in the serum and cerebrospinal fluid, and reduced CMAP with increment after brief maximum voluntary contraction in electrophysiological studies. We suggest that LEMS should be considered in the differential diagnosis of patients with CA.

Anti-Ca2+ channel antibody attenuates Ca2+ currents and mimics cerebellar ataxia in vivo

Voltage-gated Ca(2+) channels (VGCCs) are membrane proteins that determine the activity and survival of neurons, and mutations in the P/Q-type VGCCs are known to cause cerebellar ataxia. VGCC dysfunction may also underlie acquired peripheral and central nervous system diseases associated with small-cell lung cancer, including Lambert-Eaton myasthenic syndrome (LEMS) and paraneoplastic cerebellar ataxia (PCA). The pathogenic role of anti-VGCC antibody in LEMS is well established. Although anti-VGCC antibody is also found in a significant fraction of PCA patients, its contribution to PCA is unclear. Using a polyclonal peptide antibody against a major immunogenic region in P/Q-type VGCCs (the extracellular Domain-III S5-S6 loop), we demonstrated that such antibody was sufficient to inhibit VGCC function in neuronal and recombinant VGCCs, alter cerebellar synaptic transmission, and confer the phenotype of cerebellar ataxia. Our data support the hypothesis that anti-VGCC antibody may play a significant role in the pathogenesis of cerebellar dysfunction in PCA.

Paraneoplastic neurological syndromes and onconeural antibodies: clinical and immunological aspects

Paraneoplastic neurological syndromes (PNS) are infrequent disorders that are associated with cancer. The syndromes are highly heterogeneous and often affect several areas of the nervous system. Among the most well-known syndromes are paraneoplastic encephalomyelitis, cerebellar degeneration, sensory neuronopathy, and Lambert-Eaton myastenic syndrome. There are various associated tumors, in particular small cell lung cancer, cancer of the breast and ovary, and thymoma. The onset of neurological symptoms often precedes the cancer diagnosis, and the recognition of a paraneoplastic syndrome should lead to immediate search for cancer. The etiology of the paraneoplastic syndromes is believed to be autoimmune. Antibodies to onconeural antigens, expressed in the tumor of the affected individual and in normal neurons, are found in many of the patients. These antibodies are useful markers for paraneoplastic etiology. The pathogenesis of the PNS is uncertain, but cellular immune responses are thought to be the main effector mechanism. The cornerstone of therapy is the identification and treatment of the underlying malignancy. In some of the disorders, immunosuppressive therapy is of additional benefit. The prognosis of the different PNS varies depending on the level of affection and the degree of neuronal death.

Paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes (PNS) can be defined as remote effects of cancer that are not caused by the tumor and its metastasis, or by infection, ischemia or metabolic disruptions. PNS are rare, affecting less than 1/10,000 patients with cancer. Only the Lambert-Eaton myasthenic syndrome is relatively frequent, occurring in about 1% of patients with small cell lung cancer. PNS can affect any part of the central and peripheral nervous system, the neuromuscular junction, and muscle. They can be isolated or occur in association. In most patients, the neurological disorder develops before the cancer becomes clinically overt and the patient is referred to the neurologist who has the charge of identifying a neurological disorder as paraneoplastic. PNS are usually severely disabling. The most common PNS are Lambert-Eaton myasthenic syndrome (LEMS), subacute cerebellar ataxia, limbic encephalitis (LE), opsoclonus-myoclonus (OM), retinopathies (cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR), Stiff-Person syndrome (SPS), chronic gastrointestinal pseudoobstruction (CGP), sensory neuronopathy (SSN), encephalomyelitis (EM) and dermatomyositis. PNS are caused by autoimmune processes triggered by the cancer and directed against antigens common to both the cancer and the nervous system, designated as onconeural antigens. Due to their high specificity (> 90%), the best way to diagnose a neurological disorder as paraneoplastic is to identify one of the well-characterized anti-onconeural protein antibodies in the patient's serum. In addition, as these antibodies are associated with a restricted range of cancers, they can guide the search for the underlying tumor at a stage when it is frequently not clinically overt. This is a critical point as, to date, the best way to stabilize PNS is to treat the cancer as soon as possible. Unfortunately, about one-third of patients do not have detectable antibodies and 5% to 10% have an atypical antibody that is not well-characterized. As PNS are believed to be immune-mediated, suppression of the immune response represents another treatment approach.

Autoimmune and paraneoplastic channelopathies

Thirty years ago, antibodies against the muscle acetylcholine receptor (AChR) were recognized as the cause of myasthenia gravis. Since then, there has been great interest in identifying other neurological disorders associated with autoantibodies. Several other antibody-mediated neuromuscular disorders have been identified, each associated with an antibody against a ligand- or voltage-gated ion channel. The Lambert-Eaton syndrome is caused by antibodies against voltage-gated calcium channels and often occurs in patients with small cell lung cancer. Acquired neuromyotonia is caused by voltage-gated potassium channel antibodies, and autoimmune autonomic ganglionopathy is caused by antibodies against the neuronal AChR in autonomic ganglia. There is good evidence that antibodies in these disorders cause changes in synaptic function or neuronal excitability by directly inhibiting ion channel function. More recently, studies have identified ion channel antibodies in patients with certain CNS disorders, such as steroid-responsive encephalitis and paraneoplastic cerebellar ataxia. It remains unclear if antibodies can gain access to the CNS and directly cause ion channel dysfunction. Treatment of autoimmune channelopathies includes drugs that help restore normal neuronal function and treatments to remove pathogenic antibodies (plasma exchange) or modulate the immune response (steroids or immunosuppressants). These disabling neurological disorders may be dramatically responsive to immunomodulatory therapy. Future studies will likely lead to identification of other ion channel antibodies and other autoimmune channelopathies.

Management of paraneoplastic neurological syndromes: report of an EFNS Task Force

Paraneoplastic neurological syndromes (PNS) are remote effects of cancer on the nervous system. An overview of the management of classical PNS, i.e. paraneoplastic limbic encephalitis, subacute sensory neuronopathy, paraneoplastic cerebellar degeneration, paraneoplastic opsoclonus-myoclonus, Lambert-Eaton myasthenic syndrome and paraneoplastic peripheral nerve hyperexcitability is given. Myasthenia gravis and paraproteinemic neuropathies are not included in this report. No evidence-based recommendations were possible, but good practice points were agreed by consensus. Urgent investigation is indicated, especially in central nervous system (CNS) syndromes, to allow tumour therapy to be started early and prevent progressive neuronal death and irreversible disability. Onconeural antibodies are of great importance in the investigation of PNS and can be used to focus tumour search. PDG-PET is useful if the initial radiological tumour screen is negative. Early detection and treatment of the tumour is the approach that seems to offer the greatest chance for PNS stabilization. Immune therapy usually has no or modest effect on the CNS syndromes, whereas such therapy is beneficial for PNS affecting the neuromuscular junction. Symptomatic therapy should be offered to all patients with PNS.

Paraneoplastic syndromes affecting the nervous system

The paraneoplastic neurologic disorders (PND) are a diverse group of diseases characterized by the presence of neurologic dysfunction in the setting of a remote cancer. PND can affect almost any part of the nervous system, and are most commonly associated with lung cancer (small cell) and gynecologic tumors. Laboratory studies have demonstrated that an autoimmune response links the neurologic disorder and the cancer, and established a model whereby the cancer is believed to initiate the syndrome by expressing a protein antigen normally expressed in the nervous system, leading to anti-tumor immune response followed by autoimmune neurologic symptoms. We review the currently known PND and their pathogenesis.

Immunotherapy for paraneoplastic neurological disorders

Paraneoplastic disorders may affect any part of the central or peripheral nervous systems. Although relatively uncommon, these disorders are a significant cause of severe neurological disability among cancer patients. Most, if not all, neurological paraneoplastic disorders are believed to be autoimmune diseases in which an antitumour immune response also attacks neurons that express shared neuronal tumour antigens. Affected patients often have one or more circulating antineuronal antibodies, which serve as a diagnostic marker for the paraneoplastic condition, and in some cases are the direct mediators of neuronal injury. The exact immunopathogenesis and relative contributions of humoral or cellular immune effectors for most paraneoplastic syndromes are not well understood. Some patients have a gratifying neurological response to tumour treatment and/or immunotherapy, especially if the diagnosis is made early and treatment is initiated promptly. Unfortunately, many patients are left with severe and permanent neurological deficits despite aggressive treatment. This review summarises the current understanding of the clinical immunology of paraneoplastic disorders, and outlines immunotherapy options and outcomes.

Update on paraneoplastic syndromes

PURPOSE OF REVIEW

This review discusses the varied clinical spectrum of neurologic paraneoplastic disorders, describes recent advances in our understanding of autoimmunity in these disorders, and outlines a practical clinical approach to patient management.

RECENT FINDINGS

Paraneoplastic disorders may affect any part of the central or peripheral nervous system. Although relatively uncommon, these disorders are a significant cause of severe and permanent neurologic disability. Syndromes such as limbic encephalitis or opsoclonus-myoclonus should always raise suspicion of a paraneoplastic condition, but any paraneoplastic syndrome can also occur in patients without a neoplasm. Most neurologic paraneoplastic disorders are thought to be caused by an autoimmune reaction directed against 'onconeural' antigens expressed by neurons and tumor cells. Some syndromes such as Lambert-Eaton myasthenic syndrome and neuromyotonia are clearly mediated by autoantibodies. Much less is known about the immunopathogenesis of syndromes that affect the central nervous system, although a growing body of evidence implicates cellular immune effectors in causing neuronal injury. Many patients have circulating antineuronal antibodies, which can be useful in identifying a neurologic disorder as paraneoplastic and in finding the associated neoplasm. Early diagnosis of the neurologic disorder and prompt initiation of tumor treatment probably increase the likelihood of neurologic improvement.

SUMMARY

Neurologists must be able to recognize the clinical manifestations of neurologic paraneoplastic disorders, and to distinguish them from other causes of neurologic dysfunction in cancer patients. Early diagnosis of paraneoplastic syndromes maximizes the likelihood of a favorable oncologic and neurologic outcome.

Neurological channelopathies

Ion channels are membrane-bound proteins that perform key functions in virtually all human cells. Such channels are critically important for the normal function of the excitable tissues of the nervous system, such as muscle and brain. Until relatively recently it was considered that dysfunction of ion channels in the nervous system would be incompatible with life. However, an increasing number of human diseases associated with dysfunctional ion channels are now recognised. Such neurological channelopathies are frequently genetically determined but may also arise through autoimmune mechanisms. In this article clinical, genetic, immunological, and electrophysiological aspects of this expanding group of neurological disorders are reviewed. Clinical situations in which a neurological channelopathy should enter into the differential diagnosis are highlighted. Some practical guidance on how to investigate and treat this complex group of disorders is also included.

Advances in paraneoplastic neurological syndromes

PURPOSE OF REVIEW

To describe specificities and new advances in paraneoplastic neurologic syndromes (PNSs).

RECENT FINDINGS

Paraneoplastic neurologic syndromes are defined as neurologic syndromes of unknown cause that often antedate the diagnosis of an underlying, usually not clinically evident, cancer. In the last 2 decades, the discovery that many PNSs are associated with antibodies against neural antigens expressed by the tumor has suggested that some PNSs are immune-mediated. PNSs are rare and occur in less than 1% of patients with cancer. However, the diagnosis and treatment are important because the disability caused by the PNS is often severe, and the correct diagnosis usually leads to the discover of a small tumor with high chances of being cured.

SUMMARY

There is increasing recognition of an extensive variety of PNSs and of several paraneoplastic antibodies as clinical markers of these disorders. Basic immunologic studies support the pathogenic role of some of these antibodies, and basic molecular studies support the role of some antigens in neuronal degeneration and tumoral growth.

Lambert-Eaton myasthenic syndrome as an autoimmune calcium channelopathy

Lambert-Eaton myasthenic syndrome, often associated with small-cell lung carcinoma, is a disease of neuromuscular transmission in which antibodies directed against voltage-gated calcium channel (VGCC)(P/Q-type) in the motor nerve terminal play a crucial role in causing a deficient quantal release of acetylcholine. The motor nerve terminal and carcinoma cell may share a common antigen. The study using synthetic peptides and recombinant protein specified the extracellular S5-S6 linker regions in 3 of 4 domains as immunodominant sites in the molecular structure of P/Q-type VGCC alpha1 subunit. Also, the study by use of peptides and recombinant protein corresponding to synaptotagmin I suggested that in this functionally VGCC-associated presynaptic protein, the segment which exposes extracellularly during exocytosis can be immunogenic for the syndrome.

Neuro-ophthalmology and paraneoplastic syndromes

PURPOSE OF REVIEW

To describe the neuro-ophthalmological manifestations of paraneoplastic syndromes and their immunological associations.

RECENT FINDINGS

Neuro-ophthalmological signs and symptoms are usually present in paraneoplastic syndromes of the central nervous system. Unlike opsoclonus, less characteristic eye movement abnormalities are difficult to recognize as presenting symptoms of paraneoplastic syndromes. In this setting, the detection of several antibodies, including anti-Hu, Yo, Ma2, Ri, Tr, CV2/CRMP5 or voltage-gated calcium channel antibodies may help to establish that the neuro-ophthalmological disorder is paraneoplastic. Among the recently characterized antibodies, those against the Ma proteins often associate with brainstem encephalitis and vertical gaze paralysis. A small subset of patients with opsoclonus and ataxia harbor anti-Ri antibodies. In other patients, there is preliminary evidence that the autoantigens of opsoclonus reside in the postsynaptic density, but no dominant antibody marker has been identified. Uveitis and optic neuritis are rare accompaniments of paraneoplastic encephalomyelitis; some of these patients harbor anti-CV2/CRMP5 in association with other antibodies. Studies on paraneoplastic retinopathy indicate that immunity to retinal proteins other than recoverin can result in a similar syndrome to that associated with recoverin antibodies, and that melanoma-associated retinopathy may associate with several retinal antibodies.

SUMMARY

There is increasing recognition of an extensive variety of neuro-ophthalmological abnormalities as manifestations of paraneoplastic syndromes and of several antineuronal antibodies as clinical markers of these disorders. Basic immunological studies support the pathogenic role of some of these antibodies, and are elucidating the pathogenic mechanisms that underlie these and other antibody-associated paraneoplastic syndromes.

Neurologic paraneoplastic syndromes

Paraneoplastic disorders can affect any part of the central or peripheral nervous system. Although relatively uncommon, these disorders are a significant cause of severe neurologic disability among cancer patients. Many paraneoplastic disorders are believed to be caused by an autoimmune response directed against shared neural tumor antigens. This article summarizes the clinical features, possible autoimmune pathophysiology, and management issues for patients with paraneoplastic disorders.

Voltage-gated potassium channel antibodies in limbic encephalitis

We found voltage-gated potassium channel (VGKC) antibodies in 4 of 15 patients with limbic encephalitis (LE). Two patients with idiopathic LE had high VGKC antibody levels (>800 pM; controls <100 pM), that fell in parallel with a clinical response to immunotherapy. Two patients with lower VGKC antibodies (170 pM, 300 pM) had lung cancer (radiological evidence only in one) and the LE improved with immunotherapy in one. The other 11 patients without VGKC antibodies had paraneoplastic LE and eight onconeural antibodies (Hu in 6; Ma2 in 2). VGKC antibodies do not unambiguously discriminate between idiopathic or paraneoplastic LE but probably indicate a good response to immunotherapy.