syndrome
Titulaer, M.J.
Citation
Titulaer, M. J. (2010, November 24). Prediction of small cell lung cancer in the Lambert-Eaton myasthenic syndrome. Department of Neurology, Faculty of Medicine / Leiden University Medical Center (LUMC), Leiden University. Retrieved from https://hdl.handle.net/1887/16174
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CHAPTER 2
Similar epidemiological features in Lambert-Eaton myasthenic syndrome and myasthenia gravis suggest
common pathophysiological mechanisms
Abstract
Introduction Lambert-Eaton myasthenic syndrome (LEMS) and myasthenia gravis (MG) are both antibody-mediated autoimmune disorders of the neuromuscular junction. Both diseases have a tumour and a non-tumour (NT) associated form of disease. In around 50% of the patients LEMS is associated with small cell lung carcinoma (SCLC). In MG 15% of the patients have a thymoma.
Both diseases are linked to HLA-B8DR3. On the basis of age at onset, tumour and HLA-association three groups of MG patients can be distinguished. Early-onset NT-MG patients, mostly female and HLA-B8DR3 positive, late-onset patients, mostly male, without tumour or HLA-association and thirdly late-onset tumour patients, both female or male, without HLA association. We studied if similar associations could be found in patients with LEMS.
Patients and methods LEMS patients were collected from clinics in Leiden, Oxford and Nottingham, partly prospectively. Patients were classified as SCLC- LEMS or NT-LEMS if they had been tumour-free for at least 3 years.
Results We included 220 LEMS patients: 116 NT-LEMS and 104 SCLC- LEMS patients, almost equally divided over the two countries. NT-LEMS patients were younger. Young-onset NT-LEMS patients (< 40 years) were mostly female (67%), whilst the older-onset NT-LEMS (> 60 years) and SCLC-LEMS patients were mostly male (54% and 67%).
HLA data were available for 125 patients (77 NT-LEMS). In NT-LEMS patients, but not in SCLC-LEMS patients, HLA-B8, HLA-DR3 and HLA-DR3-B8-A1 were present more frequently than in controls (p < 0.0005). Of patients with early-onset NT- LEMS, 70% had HLA-B8, which lowered to 33% in late-onset NT-LEMS patients (p
~ 0.016). No difference was found between late-onset NT-LEMS patients and SCLC-LEMS patients (27%) or controls (27%). The same pattern was found for HLA-DR3 and HLA-DR3-B8-A1.
Conclusions Patients with LEMS can be separated into three groups, similar to those found in MG. NT-LEMS with early-onset , mostly female, and related to HLA- DR3-B8-A1, NT-LEMS with late-onset, equally male or female, and related to a specific HLA type. A third group consisting of patients with SCLC-LEMS with late- onset, more frequent in males, with no specific HLA association. These results suggest that common immunological factors are active in both diseases unrelated to the antigen involved.
Introduction
Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease caused by antibodies directed at the presynaptic voltage gated calcium channel (VGCC).
LEMS is a rare disorder with an incidence of 0.48 per million and a prevalence of 2.32 per million inhabitants.1 In about half the patients with LEMS a small cell lung carcinoma (SCLC) is found.2-4 These patients, invariably smokers or ex-smokers, tend to be older and present with an more progressive course of disease.5, 6 Age and sex distribution in LEMS have not been described thoroughly. In another autoimmune disease of the neuromuscular junction, myasthenia gravis (MG), the age-related incidence shows two maxima. One maximum is at young age, predominately affecting females. The second peak appears around the age of sixty years with a higher incidence for males than for females.7 In absolute numbers, as well as corrected for age, this group now represents the majority of newly diagnosed MG patients.
Although the antigenic target is different, MG and LEMS share many pathophysiological similarities. Both are antibody mediated, associated with a tumour, and non-tumour patients share the same HLA-B8-DR3 association.8-10 HLA-B8-DR3 is related to MG in young-onset patients only, while no clear association is found in late-onset MG.11 The absence of HLA-B8-DR3 is associated with a larger risk of SCLC-LEMS,5 but the relation between age of onset and HLA in non-tumour LEMS (NT-LEMS) is unknown. We postulated that, like in MG, the association between HLA and NT-LEMS might be restricted to young-onset patients.
Patients and methods
Our dataset is composed of two cohorts. The first consists of all Dutch LEMS patients with and without SCLC seen in our Neurology outpatient clinic between 1990 and 2009. Our clinic is a tertiary neuromuscular center with special interest and expertise in disorders of the neuromuscular junction. Nationwide referral and inclusion started from July 1, 1998, as described before.12 To assure complete coverage, we also checked for complete inclusion by screening all Dutch patients tested positive for anti-VGCC antibodies (commercial kit, RSR ltd, Cardiff, UK) from 2003 in the two Dutch laboratories (LUMC Leiden and ErasmusMC Rotterdam).
0 5 10 15 20 25 30 35 40 45 50
0-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90 91-95 > 95
n u m b e r o f p a ti e n ts
age at onset (years)
SCLC-LEMS males SCLC-LEMS females NT-LEMS males NT-LEMS females The second cohort was formed by British LEMS patients from Oxford and Nottingham. These patients were seen at the Neurology outpatient clinic between 1986 and 2009. All patients had been seen by the late professor John Newsom- Davis, by dr. Paul Maddison or dr. David Hilton-Jones. The clinics are both university neuromuscular clinics with specific expertise in LEMS. Only Dutch and British inhabitants were eligible for inclusion to prevent international referral bias.
Diagnostic criteria
Inclusion criteria for LEMS were the presence of clinical features (proximal muscle weakness, areflexia and autonomic symptoms),4, 13 and either the presence of serum anti-P/Q-type voltage gated calcium channel antibodies or an increment of more than 100% of the compound muscle action potential on high-frequency repetitive nerve stimulation or after maximum voluntary contraction.14, 15
Figure 1 Age at onset and gender distribution for SCLC related LEMS patients (SCLC-LEMS) and non-tumour LEMS patients (NT-LEMS)
Statistical analysis
We tested differences in clinical features between groups with SCLC-LEMS and with NT-LEMS using the Chi-square test or Fisher’s exact test when appropriate.
For continuous variables, we used the Mann-Whitney U test or Kruskal-Wallis test.
HLA frequencies were compared with a control panel of 1069 Dutch controls,5, 8 using the Chi-square test. All p-values in the tables and text are uncorrected. As the two cohorts have been collected independently, we have considered a difference statistically significant if the variable differed in both cohorts with a p- value smaller than 0.05. Exact correction for multiple comparisons is difficult to assess, as different HLA-types and the comparisons between different subgroups are not independent. P-values between 0.05 and 0.005 should be interpreted with caution and considered in combination with other calculations in the same table.
Table 1 A SCLC-LEMS NT-LEMS total p
number 58 54.2% 49 45.8% 107
age (median, range, years) 59.7 (37-77) 53.5 (15-73) 56.8 (15-77) < 0.0005
sex female 19 32.8% 27 55.1% 46 43.0% 0.020
male 39 67.2% 22 44.9% 61 57.0%
smoking ever yes 58 100.0% 29 59.2% 87 81.3% < 0.0005
no 0 0.0% 20 40.8% 20 18.7%
smoking at diagnosis yes 47 83.9% 15 30.6% 62 59.0% < 0.0005
no 9 16.1% 34 69.4% 43 41.0%
unknown 2 0
VGCC antibodies positive 53 98.1% 41 83.7% 94 91.3% 0.009
negative 1 1.9% 8 16.3% 9 8.7%
unknown 4 0
immunosuppressants yes 17 29.3% 24 50.0% 41 38.7% 0.029
ever no 41 70.7% 24 50.0% 65 61.3%
unknown 0 1
delay till diagnosis (median, range, months)
4.0 (1-40) 19.0 (2-265) 8.0 (1-265) < 0.0005
delay tumour diagnosis (median, range, months)
3.7 (-1-54) n.a.
Table 1 A Patient characteristics LEMS patients with and without SCLC, Leiden cohort. n.a. not applicable
Results
We included 220 patients, 107 in the Dutch cohort and 113 in the UK. An SCLC was found in 104 (47.3%). SCLC-LEMS patients were older than NT-LEMS patients (60.1 years vs 52.2 years at onset, p < 0.0005), in both cohorts (Table 1A and 1B). Two out of three patients with SCLC-LEMS were male, while in NT-LEMS females and males were almost equally present (Figure 1, p ~ 0.01). In young onset NT-LEMS, 69% of the patients was female, while in late-onset NT-LEMS patients the sex distribution was almost equal between male and females (p
uncorrected ~ 0.056; Table 2).
Table 1 B SCLC-LEMS NT-LEMS total
number 46 40.7% 67 59.3% 113
age (median, range, years) 61.0 (34-77) 51.7 (11-74) 55.5 (11-77) < 0.0005
sex female 17 37.0% 33 49.3% 50 44.2% 0.20
male 29 63.0% 34 50.7% 63 55.8%
smoking ever yes 44 100.0% 31 47.0% 75 68.2% < 0.0005
no 0 0.0% 35 53.0% 35 31.8%
unknown 2 1 3
smoking at diagnosis yes 37 82.2% 12 18.2% 49 44.1% < 0.0005
no 8 17.8% 54 81.8% 62 55.9%
unknown 1 1 2
VGCC antibodies positive 30 90.9% 52 86.7% 82 88.2% 0.54 negative 3 9.1% 8 13.3% 11 11.8%
unknown 13 7 20
immunosuppressants yes 29 63.0% 56 84.8% 85 75.9% 0.008
ever no 17 37.0% 10 15.2% 27 24.1%
unknown 0 1 1
delay till diagnosis (median, range, months)
3.7 (1-17) 18 (1-176) 9.3 (1-176) < 0.0005
delay tumour diagnosis (median, range, months)
4.8 (-38-68) n.a.
Table 1 B Patient characteristics LEMS patients with and without SCLC, Oxford-Nottingham cohort. n.a. not applicable
Delay between onset of symptoms and diagnosis of LEMS was much shorter in SCLC-LEMS patients than in NT-LEMS patients (3.9 months vs 18.5 months, p
< 0.0005). The delay between onset of symptoms and diagnosis of SCLC was comparable, both in the UK and in the Netherlands (4.8 months vs 3.7 months, p ~ 0.88). There was no difference between young-onset NT-LEMS and late-onset NT- LEMS with respect to delay in diagnosis (16.5 vs 18.6 months, p ~ 0.98).
Patients with SCLC-LEMS had all smoked in life and 83.2% still smoked at onset of symptoms. In NT-LEMS, British patients were less frequently smokers or former smokers than Dutch patients. 89.8% of patients had VGCC antibodies.
Frequency of VGCC antibodies did not differ significantly between SCLC-LEMS and NT-LEMS (95.4% vs 85.3%, p ~ 0.009 and p ~ 0.54 for the Dutch and English cohort, respectively).
NT-LEMS NT-LEMS NT-LEMS total p
< 40 years 40 - 60 years > 60 years
number 35 30.2% 53 45.7% 28 24.1% 116
age (median, range, years) 28.9 (11-40) 53,4 (41-60) 63.5 (60-74)
sex female 24 68.6% 23 43.4% 13 46.4% 60 51.7% 0.056
male 11 31.4% 30 56.6% 15 53.6% 56 48.3%
smoking ever yes 12 34.3% 29 55.8% 19 67.9% 60 52.2% 0.067 no 23 65.7% 23 44.2% 9 32.1% 55 47.8%
unknown 0 1 0 1
smoking at diagnosis yes 10 28.6% 9 17.3% 8 28.6% 27 23.5% 0.52 no 25 71.4% 43 82.7% 20 71.4% 88 76.5%
unknown 0 1 0 1
VGCC antibodies positive 26 81.3% 41 82.0% 26 96.3% 93 85.3% 0.36 negative 6 18.8% 9 18.0% 1 3.7% 16 14.7%
unknown 3 3 1 7
immunosuppressants yes 25 73.5% 39 73.6% 16 59.3% 80 70.2% 0.44
ever no 9 26.5% 14 26.4% 11 40.7% 34 29.8%
unknown 1 0 1 2
delay till diagnosis (median, range, months)
16.5 (1-265) 19.0 (1-176) 18.6 (3-73) 0.98
Table 2 Patient characteristics for NT-LEMS patients, subdivided by age at onset.
0 20 40 60 80
NT < 40 yr NT 40-60 yr NT > 60 yr SCLC controls
Percentage (%)
B8 DR3 DR3-B8-A1
Figure 2 HLA-DR3-B8-A1 in LEMS, related to age of onset
Treatment for LEMS was remarkably different between the two cohorts.
LEMS patients were more frequently treated with immunosuppressant medication in the UK than in the Netherlands (75.9% vs 38.7%, p < 0.0005). Nevertheless, in both countries a larger part of NT-LEMS patients was treated by immune suppression than SCLC-LEMS patients (84.8% vs 63.0% in the UK, p ~ 0.008;
50.0% vs 29.3% in the Netherlands, p ~ 0.029).
NT-LEMS SCLC-LEMS controls NT-LEMS NT-LEMS SCLC-LEMS vs SCLC-LEMS vs controls vs controls
n % n % n % P
B8 43 55,8% 13 27,1% 290 27,1% 0,0017 8,3 *10-8 0,99 34 44,2% 35 72,9% 779 72,9%
DR3 45 58,4% 12 25,0% 315 29,5% 2,6 *10-4 1,2 *10-7 0,51 32 41,6% 36 75,0% 754 70,5%
B8-DR3-A1 28 36,8% 4 8,3% 343 16,3% 4,1 *10-4 2,9 *10-6 0,14 48 63,2% 44 91,7% 1760 83,7%
Table 3 Frequencies of HLA-B8, HLA-DR3 and HLA-DR3-B8-A1 in LEMS patients with and without SCLC
NT-LEMS < 40 years 40-60 years > 60 years NT < 40 years NT > 60 years vs
NT > 60
vs SCLC
vs controls
vs SCLC
vs controls
n % n % n % p p
B8 16 70% 20 61% 7 33% 0.016 6.6 *10-4 7.3 *10-6 0.60 0.53 7 30% 13 39% 14 67%
DR3 16 70% 23 70% 6 29% 0.0066 3.2 *10-4 3.4 *10-5 0.76 0.93 7 30% 10 30% 15 71%
B8-DR3-A1 11 50% 15 46% 2 10% 0.0039 8.0 *10-5 2.5 *10-5 0.63 0.40 11 50% 18 55% 19 90%
Table 4 Frequencies of HLA-B8, HLA-DR3 and HLA-DR3-B8-A1 in NT-LEMS patients, subdivided by age at onset
DNA was available from 125 patients (77 NT-LEMS and 48 SCLC-LEMS).
HLA-B8 was associated with NT-LEMS (56%, p < 0.0005), but not with SCLC- LEMS (27%, p ~ 0.99) with respect to controls (27%, Table 3). HLA-DR3 and the complete set of HLA-DR3-B8-A1 was also associated only with NT-LEMS (58%
and 37%, respectively, p < 0.0005), but not with SCLC-LEMS (25% and 8%, p ~ 0.51 and p ~ 0.14) if compared to controls (29% and 16%).
Young-onset NT-LEMS patients differed significantly from controls (p <
0.0005, Table 4), SCLC-LEMS patients (p < 0.001) and from late-onset NT-LEMS patients for HLA-B8 (p ~ 0.016), HLA-DR3 (p ~ 0.007) and HLA-DR3-B8-A1 (p ~ 0.004, Figure 2). The NT-LEMS patients with onset between 40 and 60 years showed the same characteristics as young-onset NT-LEMS. In contrast, the results of HLA testing in the group of late-onset NT-LEMS were very similar to controls or SCLC-LEMS patients.
Discussion
Our results show that three groups of patients with LEMS can be defined according to tumour status, age at onset, sex and HLA status. This classification is strikingly similar to that described for autoimmune myasthenia gravis with acetylcholine receptor antibodies (AChR-MG).
In NT-LEMS, patients in the first group with onset before 40 were mostly female and had a high frequency of HLA-B8DR3. In the second group with onset
after the age of 60, the sex distribution was equal, and no association with HLA- B8DR3 was found. The third group with SCLC were mostly male patients and showed no HLA association.
This is very similar to AChR-MG without thymoma, were also two age- related groups of patients can be recognized. The first with onset before the age of 45, mostly female, HLA-B8DR3 positive, and a second late-onset group with increasing prevalence from the age of 60, and no clear HLA association.7, 10, 11 The only difference is the frequency of male patients in the late onset groups, which appeared higher in MG than in LEMS. HLA-B8, HLA-DR3 and HLA-DR3-B8-A1 were found more frequently in NT-LEMS,8, 9, 16 but previously no results for different specific age groups were reported.
At the start of the study it was not known which age should be chosen as the most informative cut-off point. Therefore, we separately analysed NT-LEMS patients with onset at intermediate age (40-60 years). They appeared to have a HLA pattern comparable to young-onset NT-LEMS, but a sex distribution similar to the late-onset group. Our results might have been less clear if we had not defined three groups in NT-LEMS with respect to age of onset as the results of the intermediate group would have been confusing.
Comparison with MG is difficult in this age group. Reports of epidemiological studies or natural history cohorts have used different cut-off values, differing from 40, 45 to 50 years at onset.7, 17-19 Genetic association studies have been performed for patients under the age of 40, both for HLA10 and for SNPs.20 Other studies have chosen thymus pathology (onset < 40 years or hyperplastic thymus to define as early-onset MG)11, 21, 22
or presence or absence of titin antibodies11 to separate early from late-onset disease.
The third groups consists of the SCLC-LEMS patients. These patients were older than NT-LEMS patients, and developed LEMS between the age of 55 and 65.
Again there is a MG counterpart. Thymoma associated MG has a peak after the age of 50, and like in LEMS, no clear association was found with respect to HLA.23 In contract to AChR-MG with thymoma, in SCLC-LEMS there is a male predominance, which has been shown before.4, 5, 13 This is most likely caused by the larger cigarette consumption in men as a risk factor for the development of SCLC,24 while smoking is not related to development of thymoma.
Our previous results suggested that HLA-B8 in combination with smoking history predicts the presence of SCLC in LEMS patients,5 although sensitivity and
specificity were insufficient to guide screening strategies. The results in our present study associate HLA-B8 with the early-onset group of LEMS patients, while most SCLC-LEMS patients had a late-onset. Our youngest patient with SCLC-LEMS was 34 years old, but 88% were over the age of 50 at onset. This correlation between HLA-B8 and early-onset most likely explains the negative association with SCLC.
The lack of HLA association with late-onset NT-LEMS, nor with late-onset AChR-MG without thymoma, is pathophysiologically very interesting. It poses clues to different disease pathways for tumour and non-tumour related disorders, leading eventually to the same antibody-mediated clinical disease. The lack of association between the tumour-related forms of these disorders and HLA suggests that in both diseases the tumour plays such a vital role in breaking tolerance to auto- antigens that no specific HLA-type is required. Interestingly, we found that the SCLC-LEMS patients develop more severe disease in a shorter timeframe, which might suggest a stronger stimulus provokes the immune system to start an immune response. To our knowledge it has not been studied if AChR-MG with thymoma also has a more aggressive phenotype with a more severe disease early after onset of symptoms.
It is speculative what is triggering NT-LEMS at older age. The lack of HLA association suggests a different mechanism compared to young-onset NT-LEMS. It has been suggested that these patients have eradicated an SCLC themselves without treatment. This theory is tempting but is likely to be wrong for most of them for the following reasons. The strong relation of SCLC with smoking is not so clear in late-onset NT-LEMS. The median time to diagnosis is similar to young-onset NT- LEMS, which is not compatible with a severe clinical picture depicting an aggressive immunological response eradicating an occult tumour. This does not exclude that some patients might have eradicated the tumour themselves, but this will be a small minority.
Our study summarizes results from LEMS patients collected over many years, which might have caused some bias, although comparison of the two cohorts shows remarkable similarities (Table 1A and 1B). Both cohorts were collected in tertiary centres. The age and sex distribution is comparable in LEMS patients, as well as detection of VGCC antibodies.
The British cohort of patients from Oxford contains a larger part of NT-LEMS patients because this centre is mainly focussed on neuromuscular diseases. The Dutch cohort is coordinated from a neuromuscular centre, but also had access to
patients referred by (neuro-)oncological sites. Both cohorts are composed of patients assessed both cross-sectionally and prospectively. Neither true prevalence nor incidence can be determined from these figures. Cross-sectional data will underestimate the true incidence of SCLC-LEMS. The prospective data are complete for only a few years in the Netherlands. A percentage is difficult to present, but a fraction of SCLC-LEMS amongst LEMS patients will be closer to 54% than to 41% and might even be well above it.
The frequency of smoking differed between the two cohorts. NT-LEMS patients in the UK smoked less than Dutch patients, comparable to nationwide figures.25, 26 For SCLC-LEMS patients, smoking habits are similar, underlining the importance of smoking as an important causal factor for SCLC.
Another difference is the use of immunosuppressant drugs to treat LEMS.
All patients with SCLC-LEMS, with few exceptions, were treated with chemotherapy, Chemotherapy is known to be a potent immunosuppressant.
Nevertheless, 63% of British patients received additional immunosuppressive treatment during treatment, while only 29% in the Netherlands did. Delay diagnosing LEMS nor delay diagnosing the tumour could have been an explanation as these did not differ. Careful examination of the files and clinical symptoms did not show an alternative explanation.
In conclusion, our study demonstrates that LEMS patients can be subdivided in three subgroups: SCLC-LEMS patients, early-onset NT-LEMS patients and late- onset NT-LEMS patients. These groups are comparable to MG with respect to age, sex distribution and HLA association. Further comparison between these two diseases might help to elucidate common immunopathophysiological pathways, independent of the antigens involved.
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