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PAPER |
1 Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
2 The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
Correspondence to:
Correspondence to:
J Dalmau
Department of Neurology, Division of Neuro-oncology, 3 W Gates, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA; josep.dalmau{at}uphs.upenn.edu
Received 24 June 2006
In final revised form 8 August 2006
Accepted for publication 11 September 2006
| ABSTRACT |
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Aims: (1) To determine the spectrum of limbic encephalitis identified on clinical grounds in a single institution, and compare it with that in patients referred for antibody analysis. (2) To correlate clinical outcomes with the cellular location of the autoantigens.
Methods: Prospective clinical case studies. Immunohistochemistry with rat brain, live hippocampal neurones, HeLa cells expressing Kv potassium channels and immunoblot.
Results: In 4 years, 17 patients were identified in the Hospital of the University of Pennsylvania, Philadelphia, USA, and the serum or CSF samples of 22 patients diagnosed elsewhere were also studied. 9 of our 17 (53%) patients had antibodies to known neuronal antigens (paraneoplastic or voltage gated potassium channels (VGKCs)) and 5 (29%) to novel cell-membrane antigens (nCMAg) typically expressed in the hippocampus and sometimes in the cerebellum. Considering the entire series, 19 of 39 (49%) patients had antibodies to known antigens, and 17 (44%) to nCMAg. Follow-up (248 months, median 19 months) was available for 35 patients. When compared with patients with antibodies to intraneuronal antigens, a significant association with response to treatment was found in those with antibodies to cell-membrane antigens in general (VGKC or nCMAg, p = 0.003) or to nCMAg (p = 0.006).
Conclusions: (1) 82% of patients with limbic encephalitis prospectively identified on clinical grounds had CNS antibodies; (2) responsiveness to treatment is not limited to patients with VGKC antibodies; (3) in many patients (29% from a single institution), the autoantigens were unknown but were found to be highly enriched in neuronal cell membranes of the hippocampus; and (4) these antibodies are associated with a favourable outcome.
Abbreviations: CNS, central nervous system; HUP, Hospital of the University of Pennsylvania; MRI, magnetic resonance imaging; nCMAg, novel cell-membrane antigen; VGKC, voltage-gated potassium channel
Until the mid-1990s, most cases of non-viral limbic encephalitis were considered to be paraneoplastic.1 However, there are an increasing number of reports of patients whose clinical, radiological and CSF findings suggest limbic encephalitis but whose diagnostic tests and follow-up exclude an underlying cancer.2,3 Evidence that some of these disorders are immune mediated includes the recent description of limbic encephalitis associated with antibodies to voltage-gated potassium channels (VGKC),4 the occasional association with systemic autoimmune disorders5 and frequent response to immunotherapy.6 Recent studies show that in addition to anti-VGKC, there are other limbic encephalitis-related antibodies that target novel cell-membrane antigens (nCMAg).7,8 These findings have broadened the spectrum of limbic encephalitis and suggest extensive antigen diversity. The relative frequency of these disorders is unknown because they are often unrecognised or have been excluded from most series of limbic encephalitis whose inclusion criteria are limited to patients with specific types of tumours or antibodies.1,4,912 Also, there is no single prospective institutional study reporting clinical experience with all of these disorders.
In this study, we review the clinical types and immunophenotypes of 39 patients with limbic encephalitis studied in the past 4 years, focusing on the relative distribution of patients seen by us in a single institution (n = 17) and those whose serum or CSF was referred to us for antibody analysis (n = 22). We also examine the clinical implications of identifying antibodies to known antigens and nCMAg.
| METHODS |
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Analysis of CNS antibodies
Serum and CSF samples were available from 35 patients; only serum or CSF was available from two patients each. Immunohistochemistry was performed using previously reported methods on the following: (1) rat brain sections fixed with acetone or methanolacetone (serum 1:500; CSF 1:10)14; (2) rat brain sections pre-fixed with paraformaldehyde (PFA) (serum 1:250; CSF 1:10)7; and (3) live rat hippocampal neuronal cultures (serum 1:1000; CSF 1:50).8 Additional studies included immunoblot with proteins extracted from purified human neurones, and recombinant HuD, Ma1 and Ma2, CRMP5 and amphiphysin.15 The presence or absence of VGKC was confirmed by radioimmunoassay at Athena Diagnostics (Worcester, MA, USA), and with transfected HeLa cells expressing Kv1.1, Kv1.2, Kv1.4 and Kv1.6 VGKC subunits as reported recently.16
| RESULTS |
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All serum or CSF samples of 17 patients with anti-nCMAg were negative by the radioimmunoassay, although one showed mild reactivity with cells expressing Kv1.4 (data not shown) and another with cells expressing Kv1.6 (both patients had encephalitis associated with ovarian teratoma). Both these samples produced an identical pattern of hippocampal immunolabelling8 that was clearly different from that obtained with polyclonal Kv1.4 or Kv1.6 antibodies, indicating that the main targets were other (unknown) hippocampal antigens. None of the antibodies to nCMAg of the other 15 patients reacted with cells expressing any of the indicated Kv subunits.
All antibodies (including anti-VGKC) were identified in the serum and CSF (if available). However, antibodies to nCMAg were technically easier to detect in the CSF than in serum. In 3 of 17 patients with antibodies to nCMAg, the initial studies demonstrated the antibodies only in the CSF; in all the three cases repeat studies with concentrated sera (dilution 1:100) showed the hippocampal neuropil reactivity over diffuse background staining. This background staining was similar to that found in normal control sera when used at a 1:100 dilution in PFA-fixed tissue. No background staining occured with the CSF of patients or controls.
Clinicalimmunological features
Table 2
shows the clinical and immunological features of the 17 patients seen at the HUP. Of these 17 patients, two were referred from other institutions to one of the authors on suspicion of a paraneoplastic disorder; the other 15 patients were diagnosed during their admission for neurological symptoms of unknown aetiology (n = 12) or in the outpatient clinic (n = 3). None of these 15 patients was specifically referred to the HUP or any of the authors for a paraneoplastic disorder. We included six patients with antibodies to intracellular antigens (anti-Hu, n = 4; anti-Ma2, n = 1; and atypical antibodies, n = 1), eight with antibodies to neuronal cell-membrane antigens (to nCMAg, n = 5 and to VGKC, n = 3), and three without detectable antibodies.
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Overview of immunophenotypes
The main differences among immunophenotypes of all 39 patients were as follows:
Treatment and clinical outcome
Clinical information and adequate follow-up was obtained from 35 patients. Of 29 patients with tumours, five did not receive oncologic therapy (small-cell lung cancer, n = 2; teratomas, n = 3); four of these patients died of neurological progression and one (ovarian teratoma) recovered after receiving corticosteroids and intensive care support. The other 24 patients had oncological therapy (tumour resection, n = 18; chemotherapy, n = 3; both, n = 1). All 35 patients received corticosteroids, 10 intravenous immunoglobulin, 6 plasma exchange, 7 intravenous immunoglobulin and plasma exchange (3 also received other immunosuppressants), 2 cyclophosphamide and 1 azathioprine.
The median follow-up was 19 (range 248) months. These patients were considered to be completely improved if they were able to return to work or normal daily activities. Patients were considered to be partially improved if they were not able to return to work but could function independently at home or return to most of their daily activities. In all, 22 patients had neurological improvement (tables 2
, and 3
): 3 with antibodies to intracellular antigens (Ma2, n = 2; Hu, n = 1), 12 to nCMAg, 4 to VGKC and 3 without antibodies. Of these 22 patients, 15 (Hu, n = 1; nCMAg, n = 7; VGKC, n = 4; and no antibodies, n = 3) completely improved and the other seven partially improved. Of the 13 patients who had clinical stabilisation (n = 3) or deterioration (n = 10), 9 had antibodies to intracellular antigens, 3 to nCMAg and 1 to VGKC. When compared with patients with antibodies to intracellular antigens, those with antibodies to cell-membrane antigens in general (including nCMAg and VGKC) were more likely to have neurological improvement (p = 0.003). A similar strong association with improvement was found in the subgroup of patients with antibodies to nCMAg (p = 0.006).
| DISCUSSION |
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A review of a previous series of patients with autoimmune limbic encephalitis shows that most did not adequately reflect the clinicalimmunological spectrum of the disorder because of the following:
None of these biases pertains to the 15 patients in our study who were identified on clinical grounds at the HUP and who provide a relative distribution of immunophenotypes in limbic encephalitis.
However, a referral bias was noted in the 22 patients whose sera or CSF samples were sent to us for analysis. The referral pattern seemed to be driven by our recent reports on subtypes of limbic encephalitis.7,8,10 Of the 22 patients, 17 (77%) had anti-Ma2 (23%) or antibodies to nCMAg (54%). By contrast, the frequency of anti-Ma2 encephalitis in patients in HUP was markedly lower (6%), while the occurrence of limbic encephalitis with antibodies to nCMAg remained relatively high (29%). Antibodies to nCMAg were found more frequently than anti-VGKC (18%), suggesting that many patients who are considered to have idiopathic or "non-herpetic limbic encephalitis without VGKC antibodies"6,19 may indeed have antibodies to nCMAg.
In light of the increasing number of reports on patients with limbic encephalitis and anti-VGKC, it can be argued that these patients are under-represented or were missed in our study. This is unlikely for two reasons: (1) the clinical and MRI picture of these patients with either predominant limbic encephalitis or Morvans syndrome is no more difficult to recognise than the immunophenotypes reported here; and (2) all samples from patients without antibodies to intracellular antigens were examined for anti-VGKC using at least two and in some cases three different methods (radioimmunoassay, immunohistochemistry with brain tissue, and immunocytochemistry with cells expressing Kv subunits). Although the five patients with anti-VGKC were positive by all methods used (three patients examined with all three methods), the 17 patients with antibodies to nCMAg were negative by all methods, except for two patients who showed faint reactivity with cells expressing Kv1.4 in one case and Kv1.6 in the other. In both instances, the reactivity with brain was clearly different from polyclonal Kv1.4 and Kv1.6 antibodies (data not shown), indicating that the presence of antibodies to other antigens was more restricted to the hippocampus. In previously reported patients with limbic encephalitis with anti-VGKC, the prominent antigen was Kv1.1,16 and this was also found in our three patients with anti-VGKC in whom the subunit specificity was determined.
These findings have important clinical implications:
The generally favourable outcome in most patients with antibodies to cell-membrane antigens (either VGKC or nCMAg) validates a previously suggested approach for the management of patients with limbic encephalitis.22 After reasonable exclusion of other disorders (ie, herpes simplex virus encephalitis was diagnosed in 26 patients during the same 4-year period at the HUP), patients suspected of having autoimmune limbic encephalitis should be considered for immunotherapy (corticosteroids, intravenous immunoglobulin or plasma exchange). Treatment should start even in the absence of antibody testing because patients with limbic encephalitis-VGKC or ovarian teratoma can deteriorate rapidly, with status epilepticus, hyponatraemia or hypoventilation that may result in death. Also, some patients with limbic encephalitis of unclear aetiology or without antibodies may show dramatic response to corticosteroids, as found in three of our patients.
| ACKNOWLEDGEMENTS |
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| FOOTNOTES |
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Funding: This study was supported in part by grants RO1CA89054 and RO1CA107192 (to JD) and a National Multiple Sclerosis Society grant (to KAK).
Competing interests: None declared.
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