Expression of the onconeural CV2/CRMP5 antigen in thymus and thymoma

Paraneoplastic motor disorders

Paraneoplastic neurological disorders (PNDs) are heterogeneous clinicopathologic syndromes that occur throughout the neuraxis resulting from damage to organs or tissues remote from the site of a malignant neoplasm or its metastases. The discordance between severe neurological disability and even an indolent malignancy suggests an underlying neuroimmunologic host immune response that inflicts nervous tissue damage while inhibiting malignant tumor growth. Motor system involvement, like other symptoms and signs, is associated with focal or diffuse involvement of the brain, spinal cord, peripheral nerve, neuromuscular junction or muscle, alone or in combination due to an underlying neuroimmune and neuroinflammatory process targeting neural-specific antigens. Unrecognized and therefore untreated, PNDs are often lethal making early detection and aggressive treatment of paramount importance. While the combination of clinical symptoms and signs, and analysis of detailed body and neuroimaging, clinical neurophysiology and electrodiagnostic studies, and tumor and nervous system tissue biopsies are all vitally important, the certain diagnosis of a PND rests with the discovery of a corresponding neural-specific paraneoplastic autoantibody in the blood and/or spinal cerebrospinal fluid.

CRMP5 Antibodies-Diagnostic Challenges

CRMP5-associated paraneoplastic neurological syndromes (PNS) are rare, and only few studies describe larger cohorts of patients with CRMP5 antibodies. We have included 24 patients with CRMP5 antibodies and compared clinical findings with diagnostic findings from two different line assays (Ravo and Euroimmun), staining of cerebellar sections and results of a newly developed cell-based assay for detection of CRMP5 antibodies, CRMP5-CBA. We found that peripheral neuropathy and cerebellar ataxia together with lung cancer were the most common diagnoses associated with CRMP5 antibodies. CRMP5-CBA was easy to perform, identified all relevant cases for CRMP5-associated PNS and is therefore a valuable add-on for verification of CRMP5 positivity in diagnosis of PNS.

Paraneoplastic ocular syndrome: a pandora's box of underlying malignancies

Paraneoplastic syndromes affecting the visual system are a group of conditions that arise in the systemic malignancy framework. In this review, we have provided a detailed and comprehensive overview of the published literature on the various ophthalmic paraneoplastic manifestations. A systematic review of many databases has been performed to identify ample literature on the paraneoplastic syndromes related to ophthalmology. We have discussed here the clinical features, pathogenesis, and treatment strategies of various ophthalmic paraneoplastic syndromes. It can be challenging to distinguish these disorders from their non-paraneoplastic counterparts and to determine the appropriate systemic assessment for the tumour responsible, to have a proper approach towards the management of the syndrome. METHOD: We searched PubMed, Science Direct and Journal of Ophthalmology for studies published in English between 1995 and April 2020, incorporating the general search term "paraneoplastic ocular syndrome" with connecting terms relevant to subheadings-e.g. Key search terms were cancer-associated retinopathy, (CAR), melanoma-associated retinopathy, (MAR), paraneoplastic retinopathy, autoimmune retinopathy, autoimmune-related retinopathy, and optic neuropathy, (ARRON), acute zonal occult outer retinopathy, (AZOOR), paraneoplastic vitelliform maculopathy, paraneoplastic vitelliform retinopathy, bilateral diffuse uveal melanocytic proliferation, (BDUMP), paraneoplastic optic neuropathy, (PON), polyneuropathy, organomegaly, endocrinopathy, monoclona gammopathy, and skin changes syndrome (POEMS) and various other terms. References from identified studies have been reviewed and included if deemed appropriate, valid, and scientifically important. If referenced in a selected English paper, we contemplated papers in other languages too. We preferentially selected papers that have been published in the last 10 years, but we have included relevant older references.

Autoimmune encephalitis with psychiatric features in adults: historical evolution and prospective challenge

Our review aims to delineate the psychiatric spectrum of autoantibody-associated autoimmune encephalitis over time through its discoveries of antibodies. We searched in PubMed for appropriate articles depicting the first appearance and spectrum of psychiatric symptomatology in autoantibody-positive encephalitis for this narrative review. Memory impairment was first associated with autoantibodies against intracellular antigens such as anti-HuD antibodies in 1993. 8 years later, autoantibodies against cell membrane surface antigens such as voltage-gated potassium channels were described in conjunction with memory dysfunction. The spectrum of psychiatric syndromes was amplified between 1990 and 2020 to include disorientation, behavior, cognitive dysfunction, obsessive compulsive behavior and suicidality in encephalitis patients occurring together mainly with antibodies against surface antigens, less so against intracellular antigens. In general, we found no specific psychiatric symptoms underlying specific autoantibody-associated encephalitis. As fundamental data on this issue have not been systemically assessed to date, we cannot know whether our specific findings would remain from systematic studies, i.e., on the association between cerebrospinal fluid N-methyl-D-aspartate receptor antibodies in catatonia. The psychiatric symptomatology overlaps between psychiatric domains and occurs frequently in antibody-positive encephalitis. No specific psychiatric symptoms imply an underlying, specifically autoantibody-associated encephalitis. The psychiatric phenotypology associated with antibody-positive encephalitis has evolved tremendously recently, and this new evidence reveals its relevance for future diagnostic and treatment aspects of autoimmune encephalitis patients.

The role of the laboratory in the expanding field of neuroimmunology: Autoantibodies to neural targets

Accelerated identification of autoantibodies associated with previously idiopathic neurological disease has provided insights into disease mechanisms, enhanced understanding of neurological function, and opportunities for improved therapeutic interventions. The role of the laboratory in the expanding field of neuroimmunology is critical as specific autoantibody identification provides guidance to clinicians in diagnosis, prognosis, tumor search strategies, and therapeutic interventions. The number of specific autoantibodies identified continues to increase and newer testing strategies increase efficiencies in the laboratory and availability to clinicians. The need for broadly targeted efficient testing is underscored by the variability in clinical presentation and tumor associations attributable to a specific autoantibody, and conversely the various autoantibody specificities that can be the cause of a given clinical presentation. While many of the antineural antibodies were first recognized in the setting of neoplastic disease, idiopathic autoimmune neurological disease in the absence of underlying tumor is increasingly recognized. Appropriation of therapeutic modalities used to treat autoimmune disease to treat these autoantibody mediated neurological diseases has improved patient outcomes. Interaction between clinicians and laboratorians is critical to our understanding of these diseases and optimization of the clinical benefits of our increasing knowledge in neuroimmunology.

Netrin-1 receptor antibodies in thymoma-associated neuromyotonia with myasthenia gravis

OBJECTIVE

To identify cell-surface antibodies in patients with neuromyotonia and to describe the main clinical implications.

METHODS

Sera of 3 patients with thymoma-associated neuromyotonia and myasthenia gravis were used to immunoprecipitate and characterize neuronal cell-surface antigens using reported techniques. The clinical significance of antibodies against precipitated proteins was assessed with sera of 98 patients (neuromyotonia 46, myasthenia gravis 52, thymoma 42; 33 of them with overlapping syndromes) and 219 controls (other neurologic diseases, cancer, and healthy volunteers).

RESULTS

Immunoprecipitation studies identified 3 targets, including the Netrin-1 receptors DCC (deleted in colorectal carcinoma) and UNC5A (uncoordinated-5A) as well as Caspr2 (contactin-associated protein-like 2). Cell-based assays with these antigens showed that among the indicated patients, 9 had antibodies against Netrin-1 receptors (7 with additional Caspr2 antibodies) and 5 had isolated Caspr2 antibodies. Only one of the 219 controls had isolated Caspr2 antibodies with relapsing myelitis episodes. Among patients with neuromyotonia and/or myasthenia gravis, the presence of Netrin-1 receptor or Caspr2 antibodies predicted thymoma (p < 0.05). Coexisting Caspr2 and Netrin-1 receptor antibodies were associated with concurrent thymoma, myasthenia gravis, and neuromyotonia, often with Morvan syndrome (p = 0.009). Expression of DCC, UNC5A, and Caspr2 proteins was demonstrated in paraffin-embedded thymoma samples (3) and normal thymus.

CONCLUSIONS

Antibodies against Netrin-1 receptors (DCC and UNC5a) and Caspr2 often coexist and associate with thymoma in patients with neuromyotonia and myasthenia gravis.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that antibodies against Netrin-1 receptors can identify patients with thymoma (sensitivity 21.4%, specificity 100%).

Anti-collapsin response mediator protein 5 encephalitis masquerading as a low-grade brain tumour

A 71-year-old woman presented acutely with seizures; her MRI suggested a low-grade glioma of the right temporal lobe. Over the preceding 18 months, she had developed progressive limb chorea and orofacial dyskinesia. Examination showed a predominantly amnestic cognitive profile. Initial investigations were normal, but later she was found to have antibodies to collapsin response mediator protein 5 (also called CV2). Her symptoms and neuroimaging abnormalities gradually improved without treatment. Four months later, surveillance imaging with (18)F-fluorodeoxyglucose-positron-emission tomography revealed a lesion confirmed by biopsy as a TX, N2, M0 small-cell lung cancer. This case is unusual for the strikingly unilateral neuroimaging abnormalities, which led to an initial misdiagnosis, and the spontaneous symptomatic improvement without treatment. In retrospect, the co-occurrence of paraneoplastic chorea, limbic encephalitis and neuropathy in the presence of an occult lung tumour make this almost a 'full house' of symptoms associated with antibodies to collapsin response mediator protein 5. It underlines the importance in clinical reasoning of avoiding the cognitive errors of premature closure and anchoring.

Electroencephalography of autoimmune limbic encephalopathy

There is an increasing recognition of autoimmune limbic encephalopathy with the hope for earlier diagnosis and expedited and improved treatment. Although antibody testing remains the definitive clinical diagnostic feature, the presentation of a rapid dementia, behavioral changes, and seizures leads to investigation using cerebral imaging, electroencephalography, and cerebrospinal fluid to confirm the diagnosis and also to exclude similar disorders. The electroencephalographer may be asked to comment on the types of electroencephalography abnormality and provide input toward the diagnosis of limbic encephalopathy. This article reviews the literature on limbic paraneoplastic and nonparaneoplastic encephalopathies, providing descriptions and examples of the electroencephalography findings. Typically, there are patterns of slow theta and delta activity and different patterns of temporal and frontal epileptic activity.

Autoimmune limbic encephalitis

Limbic encephalitis (LE) was first described in 1960 by Brierley et al. and was defined by an acute or subacute temporal lobe epilepsy, memory loss and psychiatric disturbances. Corsellis et al. then demonstrated that LE was associated with small-cell lung cancer and a paraneoplastic origin of LE was suggested. In the 1980s, onconeuronal antibodies specific to paraneoplastic neurological syndromes were described and some of them, such as Hu-Ab, were clearly associated with LE. In the last 20 years, other onconeuronal antibodies targeting intracellular antigens were subsequently identified and LE was considered as a rare paraneoplastic neurological syndrome with a poor outcome and as mainly being associated with Hu-Ab, Ma2-Ab or CV2/CRMP5-Ab. The concept of LE has dramatically evolved since 2004, with the description of LE becoming associated with novel autoantibodies that target neuronal surface rather than intracellular antigens. In these cases, LE was not always paraneoplastic. Interestingly, these newly described LE cases offer a much better prognosis than the previous ones. At present, LE is considered to be an autoimmune disorder that can be paraneoplastic or not and could be more frequent than previously suspected. The associated antibodies lead to the classification of different subtypes of LE and are used as prognostic markers. Those that are directed against cell surface antigens could play a direct role in the neurological symptoms of LE.

Onco-neural antibodies and tumour type determine survival and neurological symptoms in paraneoplastic neurological syndromes with Hu or CV2/CRMP5 antibodies

OBJECTIVE

Anti-Hu antibodies (Hu-Ab) and anti-CV2/CRMP5 antibodies (CV2/CRMP5-Ab) have been identified in association with paraneoplastic neurological disorders. However, it is not clear whether these antibodies are associated with specific neurological symptoms or are only markers of anti-cancer immune reaction.

METHODS

To address this question, 37 patients with CV2/CRMP5-Ab and 324 patients with Hu-Ab were compared.

RESULTS

Whereas the age and sex ratio were the same between the two groups, the distribution of neurological symptoms was not. Patients with CV2/CRMP5-Ab presented more frequently cerebellar ataxia, chorea, uveo/retinal symptoms and myasthenic syndrome (Lambert-Eaton myasthenic syndrome LEMS or myasthenia gravis). They also had a better Rankin score. In contrast, dysautonomia, brainstem encephalitis and peripheral neuropathy were more frequent in patients with Hu-Ab. Limbic encephalitis occurred similarly in both groups. Small-cell lung cancer was the most frequently associated tumour in both groups of patients, while malignant thymoma was observed only in patients with CV2/CRMP5-Ab. In particular, patients with CV2/CRMP5-Ab and thymoma developed myasthenic syndrome more frequently, while patients with SCLC developed neuropathies more frequently. Chorea and myasthenic syndrome were only seen in patients with CV2/CRMP5-Ab. The median survival time was significantly longer in patients with CV2/CRMP5-Ab, and this effect was not dependent on the type of tumour.

INTERPRETATION

The data demonstrate that in patients with paraneoplastic neurological syndromes, the neurological symptoms and survival vary with both the type of associated onco-neural antibody and the type of tumour.

Extensive expression of collapsin response mediator protein 5 (CRMP5) is a specific marker of high-grade lung neuroendocrine carcinoma

The diagnosis of high-grade neuroendocrine tumors has strong clinical relevance because it identifies patients at higher risk of an unfavorable outcome who should receive multimodal treatment. However, these tumors can be mistaken for poorly differentiated nonsmall cell carcinoma or carcinoid lung tumors. In fact, no immunohistochemical marker can currently distinguish between histologic lung subtypes. Because the collapsin response mediator protein (CRMP) family is involved in an autoimmune disease associated with small cell lung carcinoma, we explored the relationship between CRMP5 expression and lung tumor behavior. Using World Health Organization morphologic criteria, 123 lung neuroendocrine tumors and 41 randomly selected non-neuroendocrine tumors were classified. CRMP5 protein expression in tumors, metastases, and healthy lung tissue was assessed using immunostaining method. Strong and extensive CRMP5 expression was seen in 98.6% of high-grade neuroendocrine lung tumors, including small cell lung carcinoma and large cell lung neuroendocrine carcinoma, but not in any of the squamous cell carcinomas or lung adenocarcinomas in our series. In contrast, the majority of low-grade neuroendocrine lung tumors were negative for CRMP5 staining, although weak CRMP5 expression was seen in some, with 2 different staining patterns of either scattered positive cells or small foci of positive cells. Our findings point at CRMP5 as a novel marker for routine pathologic evaluation of lung tumors surgical samples in distinguishing between highly aggressive neuroendocrine carcinoma and the other lung cancers.

Autoantibodies and neurodegeneration in multiple sclerosis

Neurodegeneration develops in association with inflammation and demyelination in multiple sclerosis. Available data suggest that the progressive neuroaxonal loss begins in the earliest stages of the disease and underlies the accumulation of clinical disability. The loss of neurons and their processes is driven by a complex molecular mechanism involving cellular and humoral immune histotoxicity, demyelination, reduced neurotrophic support, metabolic impairment, and altered intracellular processes. Here we survey available data concerning the role of autoreactive immunoglobulins in neurotoxicity. A better understanding of molecular pathways leading to immune-mediated neurodegeneration may have key importance in the successful treatment of the disease.

CRMP5 antibodies in patients with small-cell lung cancer or thymoma

The collapsin response mediator protein 5 (CRMP5) antibody is usually associated with paraneoplastic neurological syndrome (PNS) and small-cell lung cancer (SCLC) or thymoma. The objective of this study was to assess the frequency of CRMP5 antibodies in patients with such tumours and to see if the presence of antibodies was associated with prognosis in these cancers. A multi-well adapted immunoprecipitation assay using radiolabelled recombinant CRMP5 protein, produced by coupled in vitro transcription/translation, was used for the detection of CRMP5 antibodies. Sera from 200 patients with SCLC, 73 patients with thymoma and myasthenia gravis (MG) and from 300 healthy blood donors were examined for CRMP5 antibodies. Positive sera were also examined by immunofluorescence and immune blots. The serological results were compared with disease severity of the patients with thymoma or SCLC. CRMP5 antibodies were detected in 10/200 (5%) of the SCLC, 9/73 (12%) of the thymomas and in 2/300 (0.6%) of the healthy controls by immunoprecipitation. The antibodies were less frequently detected by immunofluorescence or immune blots. There was no significant correlation between CRMP5 antibodies and disease severity. CRMP5 antibodies are more than twice as frequent, and the antibody levels are higher in patients with thymoma and MG than in patients with SCLC. The antibodies are correlated to these tumours, but not to disease severity.

Antibodies to CRMP3-4 associated with limbic encephalitis and thymoma

We present a case with subacute limbic encephalitis (LE) and thymoma. Neither classical onconeural antibodies nor antibodies to voltage gated potassium channels (VGKC) were detected, but the serum was positive for anti-glutamic acid decarboxylase (GAD). The patient serum also stained synaptic boutons of pyramidal cells and nuclei of granule cells of rat hippocampus. The objective of the study was to identify new antibodies associated with LE. Screening a cDNA expression library identified collapsin response mediator protein 3 (CRMP3), a protein involved in neurite outgrowth. The serum also reacted with both CRMP3 and CRMP4 by Western blot. Similar binding pattern of hippocampal granule cells was obtained with the patient serum and rabbit anti-serum against CRMP1-4. The CRMP1-4 antibodies stained neuronal nuclei of a biopsy from the patient's temporal lobe, but CRMP1-4 expression in thymoma could only be detected by immunoblotting. Absorption studies with recombinant GAD failed to abolish the staining of the hippocampal granule cells. Our findings illustrate that CRMP3-4 antibodies can be associated with LE and thymoma. This has previously been associated with CRMP5.