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Department of Chronic Diseases and Ageing, Division of Mental and Physical Health, Norwegian Institute of Public Health, Bergen, NorwayDepartment of Global Public Health and Primary Care, University of Bergen, Norway
Epilepsy patients are more often prescribed drugs used to treat autoimmune diseases.
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Epilepsy patients were more often treated for type 1 diabetes mellitus.
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Epilepsy patienst were more often treated for hypothyroidism.
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Epilepsy patients were more often treated for myasthenia gravis and MS.
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Awareness of hypothyroidism in all patients with epilepsy.
Abstract
Purpose
To examine if autoimmune disorders occur with an increased frequency in patients with epilepsy. An autoimmune etiology of epilepsies has been suggested. By using data from The Norwegian Prescription Database (NorPD) we have surveyed a national cohort of patients with active epilepsy treated with antiepileptic drugs.
Methods
NorPD contains all prescriptions of drugs dispensed at pharmacies in Norway since 2004. We received data of all drugs prescribed January 2004 - June 2014 for patients receiving an antiepileptic drug.79 751 patients receiving at least two prescriptions of antiepileptic drugs with the reimbursement code for epilepsy were included. To examine autoimmune comorbidity, medications specific for autoimmune diseases were retrieved. Standardized Incidence Ratios (SIR) with 95 % confidence interval (CI) were used to determine whether the occurrence of the prescribed autoimmune drugs in the epilepsy group deviated from the general population. Subgroups stratified for sex and age were examined.
Results
The epilepsy patients were more often treated with insulin and insulin analogs, SIR 1.8 (95 % CI 1.7–1.9); thyroid substitution, SIR 1.7 (95 % CI 1.7–1.8); pyridostigmine, SIR 1.5 (95 % CI 1.1–2.1); multiple sclerosis (MS) medications, SIR 4.9 (95 % CI 4.6–5.3); and immunosuppressive drugs SIR 1.2 (95 % CI 1.1–1.2). All epilepsy subgroups were more often than expected treated with thyroid substitution.
Conclusions
Based on a large, unselected patient cohort we find that epilepsy patients more often are prescribed medications used to treat type 1 diabetes mellitus, hypothyroidism, myasthenia gravis and MS. This was true for both men and women, and in most age-groups.
]. Common for all epileptic conditions are recurrent unprovoked seizures. Epilepsy can have severe consequences for the patient, and treatment with antiepileptic drugs is strongly recommanded for most patients. There is a wide range of antiepileptic drugs, and they can be used in combination as their mode of action varies. One third of the patients, however, does not become seizure free [
The etiology of epilepsy can be structural, infectious, genetic, metabolic or immune, or a combination of these. For more than half of the patients, the etiology is unknown [
]. Comorbidity can influence the risks of epilepsy and epileptic seizures, and more knowledge about comorbidity in epilepsy should lead to a better understanding of the pathophysiology of the disorder [
]. This is due to the recent recognition of a range of rare immune epilepsies such as epilepsy caused by anti-NMDA receptor encephalitis and anti-LG1 encephalitis [
]. Further, brain autoantibodies can be detected in some patients with unexplained epilepsy suggesting an autoimmune pathogenesis of the underlying brain disorder [
The primary aim of our study was to examine if, and to what degree, autoimmune disorders occur more frequently in patients with epilepsy. Mandatory national health registries represent important sources for information regarding comorbidity and risk factors [
]. By using data from the Norwegian Prescription Database (NorPD), we have examined a full national cohort of patients with active epilepsy treated with one or more antiepileptic drugs and recorded their use of drug treatments strongly associated with several autoimmune conditions. The treatment rates in epilepsy patients were compared to equivalent groups in the general population. Thus we have been able to define the comorbid disease load in the epilepsy population.
2. Materials and methods
2.1 The Norwegian Prescription Database (NorPD)
Most medications used in Norway, including all antiepileptic drugs, are strictly prescription controlled. Our study was based on NorPD, a health registry mandatory for registration of prescriptions dispensed at Norwegian pharmacies since January 2004. NorPD comprises a complete record of prescribed medications for the entire Norwegian population since 2004. This population counted 5.1 million people in 2014. NorPD is considered a valid and reliable database [
Nearly all medications used to treat chronic diseases in Norway are reimbursed, and the disease-specific reimbursement code is registered in NorPD. This also applies for antiepileptic drugs used to treat epilepsy. The clinical indication for the prescription of antiepileptic drugs has since March 2008 in addition been registered by a diagnostic code either from the International Classification of Diseases, 10th revision (ICD-10) or from the International Classification of Primary Care, 2nd edition (ICPC-2) [
The total number of prescriptions in NorPD during the study period, January 1st 2004 to June 30th 2014, was 76 002 263. We received all prescriptions for patients who were prescribed antiepileptic drugs during this period. Because confirmed epilepsy usually is treated over time the patient had to receive and collect prescriptions of an antiepileptic drug (ATC-code N03A) at at least two different time points. The prescriptions also needed to have the correct reimbursement code (§7, Epilepsy and other organic brain diseases) or diagnose code (ICD-10 G40 or ICPC N88) for epilepsy, or both. A total of 224 patients treated with gabapentin (N03AX12) and/or pregabalin (N03AX16) and no other antiepileptic drugs, were excluded regardless of diagnostic code, as these antiepileptic drugs mainly are used for non-epileptic conditions [
]. Altogether 79 751 patients were defined to have epilepsy. This high number is explained by the ten-year inclusion period. For each year, we had between 33 0000 and 35 000 patients enrolled, which equivalents a prevalence of 0.64–0.76 %, matching the estimated prevalence in the Nordic countries oft 0,6 % [
To examine autoimmune comorbidity in patients with epilepsy, we retrieved from NorPD medications used to treat several autoimmune diseases, hereafter referred to as autoimmune drugs. We did not have the prescription codes for these drugs. The following medications were examined;
1)
Insulin and insulin analogs (ATC code A10A), excluding patients who had been dispensed oral antidiabetics (A10B) in the same period, to increase specificity for type 1 diabetes mellitus. This according to the national guidelines in Norway recommending not to treat type 2 diabetes mellitus with insulin in monotherapy [
Selective immunosuppressive drugs, semispecific for autoimmune disorders (L04A).
The epilepsy patients were grouped according to sex and age. Patients` age was defined by their age on January 1st 2004. The prescriptions of autoimmune drugs for the epilepsy patients were compared to the prescriptions of the same drugs in the same age- and sex groups in the general population. The comparison population consisted of the entire Norwegian population registered in NorPD in the study-period, apart from those with a diagnosis of epilepsy. Our study included 4 667 376 such controls Table 3.
Table 3Demographic characteristics of the epilepsy patients and the population controls.
Standardized Incidence Ratios (SIR) were used to determine whether the occurrence of prescribed autoimmune medications in the epilepsy group was higher or lower than in the general population [
]. To obtain standardized rates, we applied age- and sex-specific rates for the use of these drugs, calculated from the total population without epilepsy. These rates were used to estimate the expected number of prescribed drugs in the epilepsy group, assuming this group had the same prescription rate as the general population. The SIR was obtained by dividing the observed number of prescriptions in the epilepsy group with this expected number. Significance was determined from a 95 % confidence interval (CI) for SIR. All data processing and analyses were performed using IBM SPSS Statistics version 24.0 and Microsoft Excel 2016. The use of anonymous data retrieved from NorPD did not require approval from our regional ethics committee.
3. Results
A total of 79 751 individuals fulfilled the inclusion criteria and were defined as epilepsy patients. 29 % of these were below 30 years, and 46 % were between 30 and 60 years old Table 3. The epilepsy patients more often received medications for most autoimmune diseases examined, independent of age and sex Table 4.
Table 4Total number of epilepsy patients treated with autoimmune drugs, and the standardized incidence ratios (SIR) when compared to the general population. Women and men were also examined separately.
Total
Women
Men
Drugs (ATC group)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
Insulin and insulin analogs (A10A)
1237
1,8 (1.7–1.9)
524
1.7 (1.6–1.9)
713
1.8 (1.7–2,0)
Thyroid hormone substitution (H03AA01)
8370
1.7 (1.7–1.8)
6148
1.6 (1.6-1.6)
2222
2.2 (2.1–2.3)
Antithyroid medications (H03B)
387
1.0 (0.9–1.1)
306
1.0 (0.9–1.1)
81
1.0 (0.8–1.3)
Cholinesterase inhibitor (N07AA02)
37
1.5 (1.1–2.1)
28
2.1 (1.4–3.0)
9
0.9 (0,4-1.6)
MS drugs (L03AB07-08;L03AB13; L03AX13;L04AA23;L04AA27;L04AA31;N07XX07; N07XX09)
The epilepsy group was more often treated with insulin and insulin analogs compared to the controls, SIR 1.8 (95 % CI 1.7–1.9). This was observed for men, SIR 1.8 (95 % CI 1.7–2.0) and women, SIR 1.7 (95 % CI 1.6–1.9), and in all age groups from 20 to 79 years, SIR varying from 1.2 to 2.1 Table 4, Table 5. Adults aged 20–30 years, had SIR 1.9 (95 % CI 1.6–2.2). For the age group 40–49 years, SIR was 2.3 (95 % CI 2.0–2.6) and for the group 50–59 years, SIR was 2.4 (95 % CI 2.1–2.7) Fig. 1.
Table 5Number of epilepsy patients treated with autoimmune drugs for all age groups, and the standardized incidence ratios (SIR) when compared to the general population.
<20 years
20–29 years
30-39 years
40–49 years
50–59 years
60–69 years
70–79 years
>80 years
Drugs (ATC groups)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
n
SIR (95 % CI)
Insulin and insulin analogs (A10A)
102
1.2 (1,0–1.4)
134
1,9 (1.6–2.2)
151
1,6 (1.4–1.9)
199
2.3 (2.0–2.6)
249
2.4 (2.1–2.7)
190
1.9 (1.6–2.2)
148
1.4(1.2–1.7)
64
1.3 (1.0–1.6)
Thyroid hormone substitution (H03AA01)
444
2.9 (2.6–3.2)
572
1.9 (1.8-2-1)
1211
2.2(2.1–2.4)
1529
1.9 (1.8–2.0)
1793
1.7(1.6–1.7)
1299
1.5 (1.4–1.5)
1012
1.3(1.3–1.4)
510
1.5 (1.4–1.6)
Antithyroid medications (H03B)
16
0.9 (0.5–1.5)
23
0.6 (0.4-0.8)
68
1.1 (0.8–1.3)
89
1.2 (0.9–1.4)
76
1.0 (0.8–1.2)
60
1.2 (0.9–1.5)
41
1.0 (0.7–1.4)
14
0.8 (0,5-1.4)
Cholinesterase inhibitor (N07AA02)
1
1.1 (0.0–6.2)
2
1.9 (0.2–7.0)
5
1.7 (0.6–4.1)
5
1.9 (0.6–4.4)
8
1.7 (0.8–3.3)
9
1.7 (0.8–3.3)
6
1.2 (0.5–2.7)
1
0.7 (0.0–4.0)
MS drugs (L03AB07-08;L03AB13; L03AX13;L04AA23;L04AA27;L04AA31;N07XX07;N07XX09)
Standardized incidence ratios (SIR) with 95 % confidence intervals for insulin treatment for male (A) and female (B) patients with epilepsy compared to the general population and categorized according to age in years. Patients` age was defined by their age January 1st 2004.
Epilepsy patients were more often treated with thyroid hormone substitution, SIR 1.7 (95 % CI 1.7-1.7). SIR was 2.2 (95 % CI 2.1–2.3) for men and 1.6 (95 % CI 1.6-1.6) for women Table 4. Epilepsy patients < 20 years had the highest ratio, SIR 2.9 (95 % CI 2.6–3.2) Table 5. For men < 20 years, the SIR was 5.1 (95 % CI 4.4–5.9) Fig. 2B.
Standardized incidence ratios (SIR) with 95 % confidence intervals for treatment with thyroid hormones for male (A) and female (B) patients with epilepsy compared to the general population and categorized according to age in years. Patients` age was defined by their age January 1st 2004.
Epilepsy patients were not prescribed more antithyroid drugs when compared to the controls, SIR 1.0 (95 % CI 0.9–1.1) Table 4, Table 5. This was true for both men, SIR 1.0 (95 % CI 0.8–1.3) and women, SIR 1.0 (95 % CI 0.9–1.1) Fig. 3 (Supplementary figure).
3.4 Cholinesterase inhibitors
Epilepsy patients were treated more often with pyridostigmine, SIR 1.5 (95 % CI 1.1–2.1) Table 4 and Fig. 4 (Supplementary figure). Altogether, 37 patients in the epilepsy group received prescriptions of pyridostigmine. Eight of these were women aged 60–69 years, Fig. 4 (Supplementary figure).
3.5 Multiple sclerosis (MS) drugs
Epilepsy patients < 70 years were prescribed more medications for multiple sclerosis than the comparable controls, with SIR varying between 1.9 and 9.0 in the different age groups Table 5. The ratios were highest for patients older than 40 years with SIR 6.0–9.0, but also the younger age groups 20–39 years were more often treated with MS drugs, SIR 2.7–3.9 Fig. 5 (Supplementary figure). This was true for both men and women.
3.6 Selective immunosuppressive drugs
The epilepsy group was more often treated with selective immunosuppressive drugs than the controls, SIR 1.2 (95 % CI 1.1–1.2) Table 4. Female patients younger than 50 years, and male patients 40–49 years were the subgroups with a significant difference Table 4, Fig. 6 (Supplementary figure).
4. Discussion
Our study shows increased prescription of medications used to treat autoimmune diseases for both male and female epilepsy patients, indicating a high frequency of type 1 diabetes mellitus, hypothyroidism, myasthenia gravis and multiple sclerosis compared to the general population. Also medications used to treat autoimmune diseases that never give any structural brain lesions or brain dyfunction, such as myasthenia gravis, were more frequently prescribed for epilepsy patients. This arguing that the findings not only are explained by confounders, but in part represent a comorbidity based on common pathogenetic factors.
Our study has several strengths, determining comorbidity in a nationwide cohort with a large, unselected group of epilepsy patients. The prescriptions of antiepileptic drugs are strictly regulated by national laws and the drugs are state-funded. By using the NorPD, we ensured inclusion of all drug treated epilepsy patients in Norway, minimizing selection bias. The diagnostic and reimbursement codes secured that the patients had epilepsy. To further increase specificity, we only included patients with at least two prescriptions of one or more antiepileptic drugs, since patients with a confirmed epilepsy usually are treated over time. Prescriptions for epilepsy can be renewed regardless of consulting physician, reducing surveillance bias. For diseases with low prevalence, like myasthenia gravis, large population cohorts are needed to study comorbidity.
The epilepsy patients were more often treated with insulin and insulin analogs compared to the general population The Norwegian Directorate of Health did not recommend to treat type 2 diabetes mellitus with insulin/insulin analogs in monotherapy during the entire study period [
]. Thus, by excluding all patients who received oral antidiabetics, and only including patients who recieved insulin or insulin analogs in monotherapy the dominating part of our study group should have type1 diabetes mellitus (T1DM). Our findings are true for men and women and in nearly all age groups further strengthening a true association between epilepsy and the autoimmune disease T1DM. Our result is supported by other studies showing that patients with T1DM have an increased risk of developing epilepsy [
]. Patients with T1DM have a higher risk of cardiovascular disease and thereby a higher risk of post-stroke epilepsy. Post-stroke epilepsy is likely confounder. However, we found that epilepsy patients below 40 years who rarely have epilepsy due to cerebrovascular disease also were more often treated with insulin and insulin analogs [
Incidence and classification of new-onset epilepsy and epilepsy syndromes in children in Olmsted County, Minnesota from 1980 to 2004: a population-based study.
] and it has been suggested that autoimmunity is implicated in epilepsy as patients with T1DM have a high prevalence of epilepsy with unknown etiology [
The epilepsy group had more prescriptions of thyroid hormones than the general population.This was true for both men and women and in all age groups, but most pronounced in the younger patients. Epilepsy patients < 20 years had a near three times increase in thyroid substitution, compared to the general population. Awareness of hypothyroidism in epilepsy patients is important, especially because symptoms of hypothyroidism can mimic both side effects of antiepileptic drugs and effects of repeated epileptic seizures. Our findings are supported by previous studies showing that hypothyroidism is a frequent comorbid disease in epilepsy patients [
]. Surveillance bias may be a contributing factor as patients with epilepsy are examined thoroughly at the time of diagnosis and with regular follow-ups, often also with blood tests. Some antiepileptic drugs can induce hypothyroidism and carbamazepine, topiramate, levetiracetam and valproate are associated with low fT4 [
]. Another study found that enzyme-inducing antiepileptic drugs can reduce thyroid hormone concentrations, but that patients remain clinically euthyroid [
]. Still such patients could have been treated with thyroid hormones. Residual confounding, for instance brain tumors causing both secondary hypothyroidism and epilepsy may explain a minor part of the findings. Neverthless, the markedly increased use of thyroid substitution in the epilepsy group, and especially in the younger patients, is of interest regarding autoimmunity. Hypothyroidism has an autoimmune etiology in 50 % of the cases [
]. The severity of neuromyelitis optica spectrum disease, another autoimmune disease that can lead to epileptic seizures, is related to anti-thyroid antibody abnormalities [
Epilepsy patients were more often treated with pyridostigmine than the general population. Pyridostigmine is the drug of choice for myasthenia gravis, and is not prescribed regularly on other indications [
]. Only in exceptional cases it is used to treat rare diseases such as Lambert-Eaton myasthenic syndrome and congenital myasthenia. It is therefore a reliable surrogate marker for active myasthenia gravis. Prevalence of myasthenia gravis varies between 150 and 180 per million [
]. In our study, we found 37 patients treated with pyridostigmine among 79 751 with epilepsy, significantly more than expected. This is supported by a population-based study from the United States that found a myasthenia gravis prevalence of 0.4 % in epilepsy patients [
]. Myasthenia gravis is an autoimmune disease that does not affect the brain and therefore does not cause epilepsy secondary to structural brain lesions [
We found that epilepsy patients more often were treated with medications specific for multiple sclerosis (MS). The results were significant for both men and women and in all adult age groups. Several strengths in our study make this result reliable. The criteria and diagnostic procedures for MS have been clearly defined in the period from 2004 [
]. Treatment of MS is now aggressive, and the drugs used are MS specific. Our results show that the association between epilepsy and MS is definite, in line with previous studies [
]. Patients with primary progressive MS do not receive immunosuppressive drugs and are therefore not included, unless using fampridin (ATC N07XX07). Untreated MS patients were not identified in our study. We found that the frequency of treatment with MS specific medications in the epilepsy group increased with age, indicating that MS progression is associated with an increase in epilepsy risk. Focal MS brain pathology with cortical lesions probably explains the majority of the epilepsy comorbidity in MS and such pathology increases with age [
]. Therefore we speculate that a shared autoimmunity could explain some of the epileptic seizures in MS, despite their focal brain lesions,
Selective immunosuppressive drugs were more often used by female epilepsy patients under 50 years. This group of medications is mainly used to treat diseases like rheumatoid arthritis, lupus and psoriasis. However, they are not specific for autoimmune disorders and are used also after transplantations and for some cancers. The frequent use of selective immunosuppressive drugs in young and middle aged female epilepsy patients still supports a high autoimmune disease load in our epilepsy patients.
Our findings indicate that epilepsy and autoimmune diseases frequently coexist [
Incidence and classification of new-onset epilepsy and epilepsy syndromes in children in Olmsted County, Minnesota from 1980 to 2004: a population-based study.
]. Guidelines for detection of epilepsy comorbidity is a pressing gap in epilepsy care. Our findings increase the knowledge of comorbidity in epilepsy, and point to potential screening strategies. Optimal treatment of comorbidity leads to better epilepsy control and increased quality of life [
Our study has some limitations. Misuse of codes might lead to a small overestimation of epilepsy patients, perhaps relevant for some diabetes- and MS patients receiving treatment for neuropathic pain [
]. To reduce this risk we excluded patients that had gabapentin and/or pregabalin as their only antiepileptic treatment. The great majority of patients with confirmed epilepsy and autoimmune disorders receive drug treatment. Such treatment was a prerequisite for detection in our study. Drugs dispensed in institutions are not registered in NorPD, this mainly concerning the elderly patients. The great majority of patients receiving epilepsy and autoimmune medications in these institutions have also received such drugs either before or after being at the institution, and have thus been included in our study. Our data does not answer whether the patient got antiepileptic drugs or autoimmune treatment first, nor do we know type of epilepsy or seizure activity. We did not have reimbursement or diagnostic codes for the autoimmune medications.
5. Conclusion
Our study shows that epilepsy patients more often are prescribed medications used to treat several autoimmune diseases compared to the general population. This was true for both men and women, and in most age-groups, and also for autoimmune diseases that do not give structural brain lesions or brain dysfunction. Autoimmunity as a factor for epilepsy or for the underlying brain dysfunction, may have consequences for diagnostic procedures and treatment in some epilepsies.
Declaration of Competing Interest
Nils Erik Gilhus has received speaker`s or consulting honoraria from Octapharma, Alexion, Argenx and Ra Pharma. Anna Wie Børsheim and Anders Engeland have no conflicts of interest to report. We confirm that we have read the Journal`s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.
Appendix A. Supplementary data
The following is Supplementary data to this article:
Incidence and classification of new-onset epilepsy and epilepsy syndromes in children in Olmsted County, Minnesota from 1980 to 2004: a population-based study.
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