Drug resistant epilepsy (DRE) is a distressing problem for patients and doctors. Approximately 20-60% of epilepsy cases become resistant to antiepileptic drugs (AEDs). DRE is defined as failure to achieve seizure freedom after trials of two tolerated AEDs. Causes of apparent DRE include misdiagnosis and non-adherence. Treatment options for true DRE include further AED trials, epilepsy surgery, vagus nerve stimulation, and ketogenic diet. Resective surgery offers the highest chance of remission, especially for temporal lobe epilepsy where seizure freedom rates can be over 90%.

1. DRUG RESISTANT
EPILEPSY
DR MOHAMMAD A.S. KAMEL
CONSULTANT NEUROLOGIST

2. Distressing problem for patient and
the doctor

3.  Spontaneous remission 20—30 %.
 Remission on antiepileptic drugs 20 – 30 %.
 30 -- 40 % persistent seizure under AEDS among which DRE
included.
 Approximately 20% of patients with primary generalized epilepsy
and up to 60% of patients who have focal epilepsy develop drug
resistance during the course of their condition, which for many is
lifelong

4.  Intractable.
 Medically refractory.
 Pharmacoresistant epilepsy

5. DEFINITION
 A task force of the International League against Epilepsy
proposed that drug-resistant be defined as the failure of
adequate trials of two tolerated, appropriately chosen and
administered antiepileptic drugs (whether as monotherapy or in
combination) to achieve seizure freedom .
 They also recommended replacing the term “intractable” with
“drug-resistant” epilepsy (DRE).
 Frequency and severity of seizures are less commonly included in
a definition of DRE .
 Even infrequent seizures can have a large impact.

6. EPIDEMIOLOGY
 Because of unstandardized definitions as well as misdiagnoses, the
incidence and prevalence of DRE are somewhat uncertain .
 Estimates of the proportion of epilepsy cases that are or become
medically resistant vary between 20 and 40 percent .

7. Clincal predictors that have been
associated with DRE
 1-High seizure density(number of seizures per time)before
treatment initiation.(Mohanraj and Brodie,2006).
 2- Long history of poor seizure control(Kwan and
Brodie,2000).
 3- Early onset of seizures (Ko and Holmes,1999).
 4-More than one seizure type(Steffeburg et al. 1998).
 5- Multiple seizures after treatment
initiation(Sillanpaa,1993).

8.  6-Remote symptomatic etiology (e.g. history of head
trauma,infection,etc.)(Kwan and Brodie,2000).
 7- Certain structural abnormalities (e.g.cortical
dysplasia,hippocampal sclerosis etc.)(Semah et al,1998).
 8- Certain EEG abnormalities ,such as persistant focal
slowing(Berg et al.,2001)or high frequency of focal
epileptiform abnormalties(Ko and Holmes,1999).
 9-Mental retardation (Callaghan et al.,2007).
 10-Psychiatric comorbidity(Hitiris et al.,2007).
 11-Abnormal neurological examination(Sillanpaa,1993).
 12- History of status epilepticus (Callaghan et al.,2007).

9. Patterns of drug resistance
(Pati and Alexopoulos,2010)
1) De novo drug resistance: with newly diagnosed epilepsy for
whom the first drug was ineffective had only an 11% probability of
future success, compared with 41% to 55% in patients who had
had to stop taking the drug because of intolerable side effects or
idiosyncratic reactions.
 Most patients for whom the first drug fails will be resistant to most
and often all antiepileptic drugs.( These results suggest that seizures
in newly diagnosed patients are either easy to control or difficult to
control right from the start)

10. 2)Progressive drug resistance
 In some patients, epilepsy is initially controlled but then gradually
becomes refractory.
 This pattern may be seen, for example, in childhood epilepsies or in
patients with hippocampal sclerosis.

11. 3)Waxing and waning resistance
 In some patients, epilepsy has a waxing-and waning pattern: I e,
it alternates between a remitting (pharmacoresponsive) and
relapsing (pharmacoresistant) course.
 Patients thought to have drug-resistant epilepsy may become
seizure-free when other drugs are tried.
 Changes in drug bioavailability, local concentration of the drug
in the brain, receptor changes, the development of tolerance,
and interactions with new medications may be implicated,
though the exact mechanism is not understood

12. COMPLICATIONS OF DRE
 Increased mortality rate, estimated at 1.37 per 100 person-years .
 (SUDEP) is 40 times more likely among patients who continue to
have seizures than in those who are seizure free .
 Head injury, burns, and fractures, are seizure-related .
 DRE is also associated with disability and diminished quality of life .
 These complications of DRE result from the combined effects of
recurrent seizures, AED toxicity, comorbid depression, as well as
psychosocial factors such as excessive dependency .

13. Factors contributing to the
biological basis of DRE with
illustrative examples
 A)Disease biology (independent of the host).
 B)Drug biology.
 C)Patient characteristic.

14. Disease biology (independent to host)
 Etiology of seizures (e.g. progressive epilepsy syndromes such as
LGS,myoclonic encephalopathies).
 Severity of the disease (e.g. frequent seizures early on trigger changes
of cellular/molecular properties resulting in unstable network that can
no longer harness seizures);”intrinsic severity "hypothesis (Rogawski and
Johnson,2008).
 Abnormal network plasticity and /or changes in the epileptogenic
substrate/network(e.g .hippocampal sclerosis, cortical dysplasia)(Gorter
and Potschka,2012).
 Seizure – induced synaptic reorganization: development of epileptic
circuits within and between brain regions(e.g. mossy fiber sprouting in
the hippocampus leading to aberrant neuronal synchronization)(Beck
and Yaari,2012).
 Ion channelopathies: mutation in sodium,calicium,potassium and
ligand gated channels.

15.  Reactive autoimmunity(e.g. anti GAD antibodies,antiGM1
antibodies, antibodies against GluR3 subunit of glutamate receptor
in Rasmussen encephalitis – cause and effect relationships not
clearly established)(Kwan and Brodie,2002).
 Impaired antiepileptic drug penetration: over expression of P-
glycoprotein and MPR in epileptogenic tissue (capillary endothelial
cells,astrocytes of blood brain barrier and neurons);”drug
transporter” hypothesis(Potschka,2010).
 Altered drug target/receptors: loss of use – dependent voltage
gated sodium channels from dentate granule cells in
carbamazepine – resistant patients;” drug target “hypothesis(Marchi
et al,2004).
 Disrupted integrity of blood brain barrier ;”BBB” hypothesis(Marchi
,2012).

16. Drug biology
 Loss of anticonvulsant efficacy due to development of tolerance
with chronic administration :pharmacokinetic”metabolic”tolerance
due to induction of AED metabolizing enzymes or other drug- drug
interactions.pharmacodynamics”functional” tolerance may be due
to loss of receptor sensitivity (Loscher and Schmidt,2006).
 Restricted therapeutic/safety margin,which precludes sufficiently
high brain penetration of the active drug(Loscher and
Schmidt,2009).
 Lack of antiepileptogenic”disease modifying”properties,i.e inability
to halt or revers the progression of the disease with available seizure
– suppressing medications(with the exception of few AEDs such as
valproate,levetricetam and others ,where potential
antiepileptogenic activity has been observed in animal models;for
instance kindling and kainite models of temporal lobe epilepsy.the
clinical relevance of these findings remains unclear)(Dudek
et.al,200;Loscher and Brandt,2010)

17. Patient characteristics
 Presence of absence of genes encoding drug transporters, of which
AEDs are known substrates:e.g. genetic polymorphisms of the P-
glycoprotein encoding gene in patients with DRE (Remy and
Beck,2006).
 Polymorphisms in genes encoding drug targets may result in altered
pharmacodynamics of certain AEDs :e.g. altered neuronal sodium
channels expressing a mutant auxiliary B1- subunit encode by the
SCN1B gene (which is responsible for the monogenic epilepsy
syndrome GEFS+)exhibit reduced sensitivity to phenytoin(Lucas et
el,2005).
 Environmental influences (e.g. perinatal exposure to pathogens
predisposing the immature brain to acquired malformations of
cortical development)(Marin – Padilla,2000).

19. EVALUATION
 Establish the diagnosis of epilepsy.
 Rule out peudoDRE.
 Define the electro clinical syndrome.
 Establish the etiology of epilepsy.
 Evaluate the medical treatment.
 Select candidate for surgery.

20. Causes of apparent or false DRE
pseudopharmacoresistant
1)Diagnostic errors
a) Patients with nonepileptic events(e.g. syncope or psychogenic non epileptic
events and inappropriately treated with multiple AED).
b) Incorrect classification of epilepsy type,leading to inappropriate drug selection
(e.g.misdiagnosis of a generalized for a focal epilepsy).
c)Failure to identify an underlying causative factor (e.g. metabolic or systemic
illness).
2)Treatment errors
a. Incorrect AED selection (e.g. wrong drug for type or drug interactions leading to
decrease efficacy).
b. Inappropriate assessment of response or lack of response (e.g. drug interactions
leading to increased side effects and decreased tolerability).
c. Inappropriate dosage (e.g. injudicious reliance on “therapeutic serum
range”,blind dosage adjustments without clinical correlation,or both).

21. 3) Non adherence to therapy
a. Poor compliance ,detrimental lifestyle, alcohol misuse,etc.
b. Inadequate patient education.
c. Intolerable side effects.
d. Prohibitive cost of medication.

24. TREATMENT OPTIONS
 Resective epilepsy surgery is the treatment of choice for medically
resistant lesional partial epilepsy as this has the most likely chance of
producing remission.
 Further AED trials, vagal nerve stimulation, and the ketogenic diet
can reduce seizure frequency and improve quality of life but are
more likely to be palliative, rather than curative, treatment options

25. Antiepileptic drugs
 Further medications trials of AEDs in mono- or polytherapy can be of
benefit in individuals with epilepsy. It is important to review past
treatment trials with the patient to assess whether the dose or
frequency of dosing was adequate.
 Sequential drug trials have a small likelihood of inducing remission in
patients who have already failed two or more AED regimens. This
approach can produce remission rates estimated at 4 to 6 percent per
year, or a cumulative rate of 14 to 20 percent . Among those who do
not become seizure-free, a substantial reduction in seizure frequency is
possible; in different series, 21 to 70 percent of patients achieve a 50
percent or greater reduction in seizure frequency .
 Reduction in seizure severity may also improve patients’ quality of life .
 However, studies with long-term follow-up find that the benefit of
successive drug trials is not sustained in one-fourth or more.
 Choosing an AED with a different mechanism of action than one not
previously efficacious may maximize the benefit from subsequent drug
trials

26. Epilepsy surgery
 Resective epilepsy surgery has the best-established efficacy for
individuals with lesional temporal lobe epilepsy .
 Patients with concordant abnormalities in one temporal lobe on
MRI and EEG have a rate of seizure remission as high as 90 percent .
 Patients with nonlesional temporal lobe epilepsy also have a high
remission rate with surgical therapy.
 The efficacy is highest in patients in whom EEG and another
imaging modality (eg, SPECT, PET) reveal a consistent location of the
epileptic focus.

27.  Neocortical focal epilepsy also responds to resective surgery. As
with mesial temporal lobe epilepsy, rates of seizure remission are
highest in patients who have MRI lesions that are concordant
with the anatomic focus of seizure activity on EEG.
 However, localization using SPECT, PET can also define a seizure
focus that when surgically removed leads to seizure remission
rates that exceed 50 percent.
 Pallaitive surgical treatments (lobar and multi-lobar resections, ),
corpus callosotomy(atonic attacks in LGS) ,
multiple subpial transections (seizure begin in areas in
brain that cannot be safely removed) .
Hemispherectomy(malformations of cortical
development Rasmussen’s encephalitis ,sturge weber syndrome
and remote vescular insult)

28. Responsive neurostimulation (FDA approved
randomized control trial 37.9% reduction in seizures
versus 17.3% seizure reduction in controls) .
.

29. Under investigation
 Deep brain stimulation (approved in the European
Union)phase III randomized controlled trial 38.8%
reduction in seizures versus 22.8% in the control group.

30. External trigeminal nerve stimulation is approved in the
European union for adults and children older than 9 year with
epilepsy and depression (phase II randomized controlled trial
the responder rate was 30.2% overall)

31. t-VNS approved in the European
union.

32. Ketogenic diet —
 (high-fat, low protein) diet has demonstrated efficacy in children
with DRE, with more than one-third experiencing a 50 percent or
greater reduction in seizures
 In two small case series of adult patients, the traditional ketogenic
diet and a modified Atkins diet reduced seizure frequency by 50
percent or more in half of patients with DRE .

33. THANK YOU