Myoclonus associated with the use of gabapentin

Gabapentin-Associated Movement Disorders: A Literature Review

BACKGROUND

Gabapentin (GBP)-induced movement disorders (MDs) are under-recognized adverse drug reactions. They are commonly not discussed with patients, and their sudden occurrence can lead to misdiagnosis. This literature review aims to evaluate the clinical-epidemiological profile, pathological mechanisms, and management of GBP-associated MD.

METHODS

Two reviewers identified and assessed relevant reports in six databases without language restriction between 1990 and 2023.

RESULTS

A total of 99 reports of 204 individuals who developed a MD associated with GBP were identified. The MDs encountered were 135 myoclonus, 22 dyskinesias, 7 dystonia, 3 akathisia, 3 stutterings, 1 myokymia, and 1 parkinsonism. The mean and median ages were 54.54 (SD: 17.79) and 57 years (age range: 10-89), respectively. Subjects were predominantly male (53.57%). The mean and median doses of GBP when the MD occurred were 1324.66 (SD: 1117.66) and 1033 mg/daily (GBP dose range: 100-9600), respectively. The mean time from GBP-onset to GBP-associated MD was 4.58 weeks (SD: 8.08). The mean recovery time after MD treatment was 4.17 days (SD: 4.87). The MD management involved GBP discontinuation. A total of 82.5% of the individuals had a full recovery in the follow-up period.

CONCLUSIONS

Myoclonus (GRADE A) and dyskinesia (GRADE C) were the most common movement disorders associated with GBP.

Antiseizure Drugs and Movement Disorders

The relationship between antiseizure drugs and movement disorders is complex and not adequately reviewed so far. Antiseizure drugs as a treatment for tremor and other entities such as myoclonus and restless leg syndrome is the most common scenario, although the scientific evidence supporting their use is variable. However, antiseizure drugs also represent a potential cause of iatrogenic movement disorders, with parkinsonism and tremor the most common disorders. Many other antiseizure drug-induced movement disorders are possible and not always correctly identified. This review was conducted by searching for all the possible combinations between 15 movement disorders (excluding ataxia) and 24 antiseizure drugs. The main objective was to describe the movement disorders treated and worsened or induced by antiseizure drugs. We also summarized the proposed mechanisms and risk factors involved in the complex interaction between antiseizure drugs and movement disorders. Antiseizure drugs mainly used to treat movement disorders are clonazepam, gabapentin, lacosamide, levetiracetam, oxcarbazepine, perampanel, phenobarbital, pregabalin, primidone, topiramate, and zonisamide. Antiseizure drugs that worsen or induce movement disorders are cenobamate, ethosuximide, felbamate, lamotrigine, phenytoin, tiagabine, and vigabatrin. Antiseizure drugs with a variable effect on movement disorders are carbamazepine and valproate while no effect on movement disorders has been reported for brivaracetam, eslicarbazepine, lacosamide, and stiripentol. Although little information is available on the adverse effects or benefits on movement disorders of newer antiseizure drugs (such as brivaracetam, cenobamate, eslicarbazepine, lacosamide, and rufinamide), the evidence collected in this review should guide the choice of antiseizure drugs in patients with concomitant epilepsy and movement disorders. Finally, these notions can lead to a better understanding of the mechanisms involved in the pathophysiology and treatments of movement disorders.

Movement disorders associated with antiseizure medications: A systematic review

New-onset movement disorders have been frequently reported in association with the use of antiseizure medications (ASMs). The frequency of specific motor manifestations and the spectrum of their semiology for various ASMs have not been well characterized. We carried out a systematic review of literature and conducted a search on CINAHL, Cochrane Library, EMBASE, MEDLINE, PsycINFO, and Scopus from inception to April 2021. We compiled the data for all currently available ASMs using the conventional terminology of movement disorders. Among 5123 manuscripts identified by the search, 437 met the inclusion criteria. The largest number of reports of abnormal movements were in association with phenobarbital, valproic acid, lacosamide, and perampanel, and predominantly included tremor and ataxia. The majority of attempted interventions for all agents were discontinuation of the offending drug or dose reduction which led to the resolution of symptoms in most patients. Familiarity with the movement disorder phenomenology previously encountered in relation with specific ASMs facilitates early recognition of adverse effects and timely institution of targeted interventions.

Negative myoclonus associated with tramadol use

Negative myoclonus (NM) is a shock-like jerky involuntary movement caused by a sudden, brief interruption of tonic muscle contraction. NM is observed in patients diagnosed with epilepsy, metabolic encephalopathy, and drug toxicity and in patients with brain lesions. A 55-year-old man presented with NM in both his arms and neck. He has taken medications containing tramadol at a dose of 80–140 mg/day for 5 days due to common cold. He had no history of seizures. Acute lesions were not observed during magnetic resonance imaging, and abnormal findings in his laboratory tests were not noted. His NM resolved completely after the discontinuation of tramadol and the oral administration of clonazepam. Our case report suggests that tramadol can cause NM in patients without seizure history or metabolic disorders, even within its therapeutic dose.

Negative myoclonus associated with pregabalin

Negative myoclonus (NM) is a jerky, shock-like involuntary movement caused by a sudden, brief interruption of muscle contraction. An 80-year-old man presented with multifocal NM and confusion. Two days before the onset of NM, he commenced the intake of pregabalin at a dose of 150 mg/day for neuropathic pain. His NM resolved completely and mental status improved gradually after the administration of lorazepam intravenously and the discontinuation of pregabalin. Our study suggests that pregabalin can cause NM even in patients without a history of seizures.

Dealing with the storm: An overview of seizure precipitants and spontaneous seizure worsening in drug-resistant epilepsy

In drug-resistant epilepsy, periods of seizure stability may alternate with abrupt worsening, with frequent seizures limiting the individual's independence and physical, social, and psychological well-being. Here, we review the literature focusing on different clinical scenarios related to seizure aggravation in people with drug-resistant epilepsy. The role of antiseizure medication (ASM) changes is examined, especially focusing on paradoxical seizure aggravation after increased treatment. The external provocative factors that unbalance the brittle equilibrium of seizure control are reviewed, distinguishing between unspecific triggering factors, specific precipitants, and 'reflex' mechanisms. The chance of intervening surgical or medical conditions, including somatic comorbidities and epilepsy surgery failure, causing increased seizures is discussed. Spontaneous exacerbation is also explored, emphasizing recent findings on subject-specific circadian and ultradian rhythms. Awareness of external precipitants and understanding the subject-specific spontaneous epilepsy course may allow individuals to modify their lifestyles. It also allows clinicians to counsel appropriately and to institute suitable medical treatment to avoid sudden loss of seizure control.

Negative myoclonus induced by gabapentin and pregabalin: A case series and systematic literature review

INTRODUCTION

Negative myoclonus is a jerky, brief, and sudden interruption of voluntary muscle contraction. Although gabapentin and pregabalin have been reported to induce positive myoclonus in some patients with impaired renal function, there are only a few studies describing pregabalin- or gabapentin-induced negative myoclonus. This study reviewed patients who had developed pregabalin- or gabapentin-induced negative myoclonus.

METHODS

We collected the patients with negative myoclonus who were referred to the department of neurology at a university-affiliated hospital and selected pregabalin- or gabapentin-induced negative myoclonus. Then reviewed the literature with respect to pregabalin- or gabapentin-induced negative myoclonus.

RESULTS

A total of 77 patients with negative myoclonus were reviewed. Among them, 21 neuropathic pain patients who were prescribed and developed negative myoclonus induced by pregabalin (9 cases) or gabapentin (12 cases). To prove causality of the drug, probable and certain level of category according to the WHO-UMC criteria were recruited. Of the 21 patients, 3 had impaired renal function, while 18 had normal renal function. Review of the literature identified 7 further cases (6 had normal renal function) with pregabalin- or gabapentin-induced negative myoclonus.

CONCLUSION

Pregabalin- and gabapentin-induced negative myoclonus can develop even in patients with normal renal function. Physicians should keep in mind the possibility of patients developing negative myoclonus under treatment of pregabalin or gabapentin even in short period of time and with low dosage, and in the normal range of renal function. Further prospective study investigating incidence and risk factors is warranted.

Tolerability and Safety of Commonly Used Antiepileptic Drugs in Adolescents and Adults: A Clinician's Overview

This paper discusses the issues surrounding the tolerability and safety of the commonly used antiepileptic drugs (AEDs) in adolescents and adults. The content includes dose-related adverse effects, idiosyncratic reactions, behavioural and psychiatric comorbidities, chronic problems, enzyme induction and teratogenesis. Twenty-one AEDs are discussed in chronological order of their introduction into the UK, starting with phenobarbital and ending with brivaracetam. Wherever possible, advice is given on anticipating, recognising and managing these issues and thereby improving the lives of people with epilepsy, most of whom will need to take one or more of these agents for life. Avoidance of side effects will increase the possibility of achieving and maintaining long-term seizure freedom. Alternatively, adverse events from AEDs will substantially reduce quality of life and often result in higher healthcare costs.

The clinical heterogeneity of drug-induced myoclonus: an illustrated review

A wide variety of drugs can cause myoclonus. To illustrate this, we first discuss two personally observed cases, one presenting with generalized, but facial-predominant, myoclonus that was induced by amantadine; and the other presenting with propriospinal myoclonus triggered by an antibiotic. We then review the literature on drugs that may cause myoclonus, extracting the corresponding clinical phenotype and suggested underlying pathophysiology. The most frequently reported classes of drugs causing myoclonus include opiates, antidepressants, antipsychotics, and antibiotics. The distribution of myoclonus ranges from focal to generalized, even amongst patients using the same drug, which suggests various neuro-anatomical generators. Possible underlying pathophysiological alterations involve serotonin, dopamine, GABA, and glutamate-related processes at various levels of the neuraxis. The high number of cases of drug-induced myoclonus, together with their reported heterogeneous clinical characteristics, underscores the importance of considering drugs as a possible cause of myoclonus, regardless of its clinical characteristics.

Effect of gabapentin pretreatment on myoclonus after etomidate: a randomized, double-blind, placebo-controlled study

AIM

To evaluate the effects of three different doses of gabapentin pretreatment on the incidence and severity of myoclonic movements linked to etomidate injection.

METHOD

One hundered patients, between 18 and 60 years of age and risk category American Society of Anesthesiologists I-II, with planned elective surgery under general anesthetic were included in the study. The patients were randomly divided into four groups and 2h before the operation were given oral capsules of placebo (Group P, n=25), 400mg gabapentin (Group G400, n=25), 800mg gabapentin (Group G800, n=25) or 1200mg gabapentin (Group G1200, n=25). Side effects before the operation were recorded. After preoxygenation for anesthesia induction 0.3mgkg(-1) etomidate was administered for 10s. A single anesthetist with no knowledge of the study medication evaluated sedation and myoclonic movements on a scale between 0 and 3. Two minutes after induction, 2μgkg(-1) fentanyl and 0.8mgkg(-1) rocuronium were administered for tracheal intubation.

RESULTS

Demographic data were similar. Incidence and severity of myoclonus in Group G1200 and Group G800 were significantly lower than in Group P; sedation incidence and level were appreciably higher compared to Group P and Group G400. While there was no difference in the incidence of myoclonus between Group P and Group G400, the severity of myoclonus in Group G400 was lower than in the placebo group. In the two-hour period before induction other than sedation none of the side effects related to gabapentin were observed in any patient.

CONCLUSION

Pretreatment with 800mg and 1200mg gabapentin 2h before the operation increased the level of sedation and reduced the incidence and severity of myoclonic movements due to etomidate.

Myoclonus in renal failure: Two cases of gabapentin toxicity

Gabapentin, an AED approved for the adjunctive treatment of partial seizures with/without secondary generalization and for the treatment of postherpetic neuralgia, is frequently used off-label for the treatment of both psychiatric and pain disorders. Since gabapentin is cleared solely by renal excretion, dosing requires consideration of the patient's renal function. Myoclonic activity may occur as a complication of gabapentin toxicity, especially with acute kidney injury or end-stage renal disease. We report 2 cases of myoclonic activity associated with gabapentin toxicity in the setting of renal disease which resolved with discontinuation of gabapentin and treatment with hemodialysis and peritoneal dialysis. As gabapentin has multiple indications and off-label uses, an understanding of myoclonus, neurotoxicity, and renal dosing is important to clinicians in multiple specialties.

lennox-Gastaut syndrome: an updateon treatment

Lennox-Gastaut syndrome (LGS) is a severe epileptic encephalopathy. Few current treatment options are effective in improving seizure control. This paper reviews the available treatments of LGS and discusses a new option in Canada, rufinamide. It is a wide spectrum anticonvulsant, approved in a number of countries for the treatment of LGS. In a randomized controlled trial in the LGS population, adjunctive rufinamide therapy has been shown to offer significantly greater reduction in total seizure frequency and tonic-atonic seizure frequency in comparison to placebo. Efficacy has been assessed over three years and appears to be sustained. Most adverse events were cognitive (e.g. somnolence) or gastrointestinal in nature and in many cases transient or mild. based on the efficacy and safety data on rufinamide obtained to date, this medication will provide additional benefits to patients with LGS in Canada and is an important consideration for our patients in the adjunctive treatment setting.

Treatment of gabapentin-induced myoclonus with continuous renal replacement therapy

A 56-year-old man with diabetes, hypertension, and chronic kidney disease presented to the emergency room with a complaint of pain in his right foot. He was found to have tremors. Gabapentin toxicity was suspected and the patient was found to have high gabapentin level (6.3 mcg/ml). Patient was commenced on continuous venovenous hemodiafiltration (CVVHD) and the pharmacokinetics of gabapentin was studied. The patient improved symptomatically and his tremors subsided. In this case report, we describe the successful management of gabapentin toxicity with continuous renal replacement therapy and calculate the clearance of gabapentin which will enable future treatment of gabapentin toxicity by CVVHD.

[Epilepsy practice for neurologists]

Epilepsy is a common disease with a high incidence of about one percent. Knowledge of seizure semiology and correct reading of EEG findings are important for diagnosis of epilepsy. Because the primary therapy for epilepsy is antiepileptic drugs (AEDs), including several ones that are newly permitted in Japan, we need to prescribe them based on an understanding of their actions and interaction mechanisms. However, we also need to consider early surgical treatment for temporal lobe epilepsy with hippocampal sclerosis. In the therapeutic decision for adult epilepsy patients many factors such as employment, marriage, child bearing, and co-existent disease need to be considered. The present review provides an overview of the basis of epilepsy practice for neurologists treating adults with epilepsy, including a discussion of new AEDs, epilepsy surgery, women with epilepsy, and epilepsy in the elderly.

The safety and tolerability of newer antiepileptic drugs in children and adolescents

The newer antiepileptic drugs (AEDs) provide more therapeutic options and overall improved safety and tolerability for patients. To provide the best care, physicians must be familiar with the latest tolerability and safety data. This is particularly true in children, given there are relatively fewer studies examining the effects of AEDs in children compared with adults. Since we now have significant paediatric literature on each of these agents, we provide a comprehensive and current literature review of the newer AEDs, focusing on safety and tolerability data in children and adolescents. Because the safety profiles in children differ from those in adults, familiarity with this literature is important for child neurologists and other paediatric caregivers. We have organized the data by organ system for each AED for easier reference.

Selection of antiepileptic drugs in adults

Epilepsy affects approximately 50 million people worldwide, with an annual incidence of 50 to 70 cases per 100,000 population. The condition can strike at any time of life, with an immediate impact on everyday activities and routine. Key to optimal management is swift referral to an epilepsy specialist, appropriate investigation, and timely institution of antiepileptic drug therapy. In the past 20 years, the explosion of 13 new agents into the marketplace has greatly increased the potential for therapeutic intervention. This article explores the rationale for treatment selection in adults with epilepsy.

Myoclonus

PURPOSE OF REVIEW

This review examines recent developments in the field of myoclonus.

RECENT FINDINGS

The range of clinical features in myoclonic dystonia has been extended and its underlying pathophysiology better defined. The diverse causes leading to jerky tremor and orthostatic myoclonus have been clarified and the need to consider drugs as potential causes highlighted. In patients with combined myoclonus and epilepsy, the major advance has been in our understanding of the natural history of these conditions, which can be more benign than hitherto thought. Finally, the new condition of primary progressive myoclonus of ageing has been identified, although it remains to be seen whether this is a pathological entity or not.

SUMMARY

Most progress has been in the characterization of myoclonic syndromes with dystonia and epilepsy. Therapeutic options remain limited, and exploration of the role of functional neurosurgery may be worthwhile in the future, given the debilitating nature of many myoclonic syndromes.

[Development or worsening of myoclonus associated with gabapentin therapy]

PURPOSE

To evaluate the development or worsening of myoclonus in patients receiving gabapentin (GBP).

METHODS

Clinical charts of 162 patients treated with GBP were reviewed concerning development or worsening of myoclonus.

RESULTS

We found 3 cases (1.9%) of myoclonus. Two patients had preexisting myoclonus and generalized tonic-clonic seizures, while the other one had generalized tonic-clonic seizures only. All patients experienced development or worsening of myoclonus within 2 weeks after starting GBP. Dose at the onset of development or worsening of myoclonus varied from 600 mg to 1,800 mg. Two patients developed multifocal myoclonus. Discontinuation of GBP or clonazepam add-on resulted in cessation of myoclonus with no serious sequela.

CONCLUSION

GBP may increase the risk of development of de novo myoclonus or worsening of myoclonus in patients with preexistent myoclonus. According to the result of this study and the treatment guidelines, GBP should be avoided when a patient has preexistent myoclonus.

CNS adverse events associated with antiepileptic drugs

A variety of newer antiepileptic drugs (AEDs) are now available for treating patients with epilepsy in addition to the 'conventional' drugs that have been available throughout a large part of the last century. Since these drugs act to suppress the pathological neuronal hyperexcitability that constitutes the final substrate in many seizure disorders, it is not surprising that they are prone to causing adverse reactions that affect the CNS.Information on adverse effects of the older AEDs has been mainly observational. Equally, whilst the newer drugs have been more systematically studied, their long-term adverse effects are not clearly known. This is illustrated by the relatively late emergence of the knowledge of visual field constriction in the case of vigabatrin, which only became known after several hundred thousand patient-years of use. However, older drugs continue to be studied and there has been more recent comment on the possible effect of valproate (valproic acid) on cognition following exposure to this drug in utero.With most AEDs, there are mainly dose-related adverse effects that could be considered generic, such as sedation, drowsiness, incoordination, nausea and fatigue. Careful dose titration with small initial doses can reduce the likelihood of these adverse effects occurring. Adverse effects such as paraesthesiae are more commonly reported with drugs such as topiramate and zonisamide that have carbonic anhydrase activity. Weight loss and anorexia can also be peculiar to these drugs. Neuropsychiatric adverse effects are reported with a variety of AEDs and may not be dose related. Some drugs, such as carbamazepine when used to treat primary generalized epilepsy, can exacerbate certain seizure types. Rare adverse effects such as hyperammonaemia with valproate are drug specific. There are relatively very few head-to-head comparisons of AEDs and limited information is available in this regard.In this review, we discuss the available literature and provide a comprehensive summary of adverse drug reactions of AEDs affecting the CNS.

Adjunctive pregabalin therapy in mentally retarded, developmentally delayed patients with epilepsy

This retrospective study evaluated the efficacy and tolerability of adjunctive pregabalin (PGB) therapy in mentally retarded, developmentally delayed patients. The primary efficacy measure was the change in the median frequency of seizure days per week between the baseline (8 weeks prior to initiating PGB) and treatment (12 weeks of titration and maintenance) periods. Inclusion criteria were: documented epilepsy treated with antiepileptic drug, at least one seizure during the baseline period, and lack of prior exposure to PGB. Seven patients (four female, three male, mean age=43) with multiple seizure types (generalized tonic-clonic, tonic, partial, and atypical absence) met the inclusion criteria. The mean dose of PGB was 293 mg/day (range=150-350 mg/day). PGB was efficacious, resulting in a significant reduction in the median frequency of seizure days/week between baseline and treatment (1.38 vs 0.50, P=0.018). The 50% responder rate was 71%. The adverse effects at last follow-up (mean 13 months) included weight gain, myoclonus, and sedation.

Pregabalin-induced cortical negative myoclonus in a patient with neuropathic pain

Myoclonus is a well-known side effect of anticonvulsant drugs. Pregabalin is one of the newer drugs approved for the treatment of focal epilepsies. Frequently it is also used to treat chronic pain syndromes. We describe a patient who, after receiving his first dose of pregabalin to relieve neuropathic pain, presented with a negative myoclonus. Clinical aspects and electrophysiological data such as polygraphic studies, electroencephalography, and measurement of somatosensory evoked potentials support the cortical origin of negative myoclonus. Our findings reveal that even in patients without a history of seizures, pregabalin can cause a cortical negative myoclonus.

Myoclonus induced by the use of gabapentin

Myoclonus is a rare side effect of gabapentin (GBP) and has been reported in patients with preexisting myoclonus, mental retardation, chronic static encephalopathy, diffuse brain damage, impaired renal function, or end stage renal disease. We report a case of myoclonus in a patient with normal renal function and no previous disorders. A 69-year-old female underwent diskectomy and foraminotomy at the left L4-L5 level. Postoperatively, she complained of paresthesia in her left leg, which was thought to be due to root manipulation during surgery. To relieve the paresthesia, she was given tramadol, an oral opioid agonist, and GBP. One week after GBP was increased to 900 mg per day, myoclonus developed, which severely impaired her normal activity. Her symptoms resolved 2 days after discontinuation of GBP. The coadministration of tramadol and GBP may mutually enhance the myoclonic potential of each drug. The causal relationship between GBP and myoclonus was suggested by cessation of myoclonus after GBP discontinuation despite continued therapy with tramadol.

Advancements in the Treatment of Epilepsy

Diagnostic tools and treatment options for epilepsy have expanded in recent years. Imaging techniques once confined to research laboratories are now routinely used for clinical purposes. Medications that were unavailable a few years ago are now first-line agents. Patients with refractory seizures push for earlier surgical intervention, consider treatment with medical devices, and actively seek nonpharmacologic alternatives. We review some of these recent advances in the management of epilepsy.

Life-Threatening Status Epilepticus Following Gabapentin Administration in a Patient with Benign Adult Familial Myoclonic Epilepsy

We report the case of a 57-year-old man who experienced life-threatening myoclonic status after the administration of gabapentin. Based on familial data, the patient was determined to be a member of a previously described family with benign adult familial myoclonic epilepsy (BAFME). The myoclonic status did not respond to benzodiazepines, but resolved after discontinuing the gabapentin. As for other idiopathic generalized epilepsies, gabapentin may precipitate myoclonic status in a benign syndrome, such as BAFME, as is reported herein for the first time. A correct diagnosis and prompt discontinuation of the drug may reverse a potentially severe, life-threatening condition.

Gabapentin and pregabalin for chronic neuropathic and early postsurgical pain: current evidence and future directions

PURPOSE OF REVIEW

Gabapentin and pregabalin bind to the alpha-2-delta calcium channel subunit and represent a novel analgesic drug class. The evidence base supporting their use for chronic neuropathic and early postsurgical pain is reviewed.

RECENT FINDINGS

Multiple, large, high-quality trials have demonstrated the safety and efficacy of gabapentin and pregabalin in neuropathic pain. Treatment-related improvement of pain and sleep positively impact upon quality of life. Sedation, dizziness and ataxia are important and relatively common adverse effects, however. Accumulating evidence indicates that gabapentin, and possibly pregabalin, also exert important effects following surgery. Multiple high-quality trials have demonstrated analgesic and opioid-sparing efficacy with gabapentin following various surgical procedures. Gabapentin and pregabalin reduce movement-evoked pain and this can lead to enhanced functional postoperative recovery. Postoperative opioid sparing is of questionable relevance since few trials have shown reduced opioid-related adverse effects. Sedation, dizziness and ataxia have been reported in only a few trials. Future larger-scale perioperative trials focused on safety assessment are needed, however.

SUMMARY

Gabapentin and pregabalin are efficacious treatments for neuropathic and postsurgical pain. Future research addressing several specific questions would serve to better delineate their optimal roles in treating these and other pain conditions.

Drug-induced myoclonus: a French pharmacovigilance database study

Various drugs have been reported to induce myoclonus. However, this adverse event is not well known because of the difficult diagnosis and the lack of pharmaco-epidemiological or controlled studies. As far as we know, there are only case reports. In the literature, antiparkinsonian medications, antipsychotics, antidepressants, anesthetics, opiates and anti-infectious drugs have been reported in the occurrence of myoclonus. In a French pharmacovigilance database study, only 423 reports (0.2%) involved drug-induced myoclonus. The median age of patients was 55 years and 10% of these patients had a concomitant neurological disease. Only 16% of these reports had a strong imputability score (likely). The most frequently involved drugs were anti-infectious (15%), antidepressants (15%), anxiolytics (14%), and opiates agents (12%). Fifty-six percent of these reports were classified as serious adverse event. Concerning outcome, most patients (84%) recovered without sequels.

Aggravation of epilepsy by anti-epileptic drugs

The possibility that so-called anti-epileptic drugs (AEDs) may aggravate epilepsy must always be borne in mind by the clinician. Many reports of such aggravation of seizures have been published. Most such reports are anecdotal and speculative, and suggest that many such reactions are idiosyncratic. However, for some there is a sufficient body of evidence to suggest that some AEDs used in certain epilepsies may consistently cause worsening of seizures. Seizure aggravation may include increase in the frequency or severity of existing seizures, emergence of new types of seizure, or the occurrence of status epilepticus. The pathophysiology of seizure aggravation is poorly understood including non-specific effects such as those associated with sedation, drug-induced encephalopathy, and paradoxical or inverse pharmacodynamic effects. For some epilepsies the choice of AEDs may be inappropriate, and although the mechanism of seizure aggravation is not clear, its occurrence may be fairly predictable. This is best documented for the use of carbamazepine in idiopathic generalized and myoclonic epilepsies. Most other AEDs have been reported occasionally to cause seizure aggravation. The lowest risk of seizure aggravation appears to be with valproate. Risk factors for worsening of seizures are epileptic encephalopathy, polytherapy, high frequency of seizures, and cognitive impairment. Advances in pharmacogenomics may in the future enable such adverse effects to be predicted for individual patients. Meanwhile, a systematic approach to reporting AED-induced seizure aggravation should be developed.

Absence and myoclonic status epilepticus precipitated by antiepileptic drugs in idiopathic generalized epilepsy

Aggravation of idiopathic generalized epilepsy (IGE) syndromes by inappropriate antiepileptic drugs (AEDs) is increasingly recognized as a serious and common problem. Precipitation of status epilepticus (SE) by inappropriate medication has rarely been reported. We retrospectively studied all adult patients with IGE taking at least one potentially aggravating AED, who developed video-EEG documented SE over 8 years, and whose long-term outcome was favourable after adjustment of medication. We identified 14 patients (seven male patients) aged 15-46 years with a mean duration of epilepsy of 16.4 years. Video-EEG demonstrated typical absence SE (ASE) in five, atypical ASE in five, atypical myoclonic SE (MSE) in three and typical MSE in one. Epilepsy had been misclassified as cryptogenic partial in eight cases and cryptogenic generalized in four. The correct diagnosis proved to be juvenile absence epilepsy (JAE) in six patients, juvenile myoclonic epilepsy (JME) in four, epilepsy with grand mal on awakening (EGMA) in two and childhood absence epilepsy (CAE) in two. All patients had been treated with carbamazepine (CBZ) and had experienced seizure aggravation or new seizure types before referral. Seven patients had polytherapy with phenytoin (PHT), vigabatrin (VGB) or gabapentin (GBP). Potential precipitating factors included dose increase of CBZ or of CBZ and PHT; initiation of CBZ, VGB or GBP; and decrease of phenobarbital. Withdrawal of the aggravating agents and adjustment of medication resulted in full seizure control. This series shows that severe pharmacodynamic aggravation of seizures in IGE may result in ASE or MSE, often with atypical features.

The management of idiopathic generalized epilepsies

Idiopathic generalized epilepsies (IGEs) are a well defined group of epilepsies, with onset predominantly in childhood. Recent evidence suggests that IGEs may also be prevalent but under-diagnosed in adults. IGEs respond well to appropriate treatment and 80-90% of cases become fully controlled. However, correct identification of IGE and selection of a broad-spectrum antiepileptic drug (AED) is crucial if cases of 'pseudo-intractability' are to be avoided. Preliminary evidence suggests that some of the newer AEDs are broad spectrum and may offer advantages in the treatment of IGEs. There is strong evidence that childhood-, adolescent- and adult-onset IGEs share biologic determinants and are best viewed as a spectrum or continuum of conditions. The diagnosis of IGE, even as a group, is very important for proper management.

Gabapentin-Induced Neurologic Toxicities

Gabapentin is an antiepileptic drug approved for the treatment of postherpetic neuralgia and as adjunctive therapy for partial seizures. The drug has been shown to be safe and nontoxic. The current literature has limited reports of neurologic toxicity associated with gabapentin therapy in patients with or without renal dysfunction. We describe the case of a 75-year-old man with renal dysfunction who developed neurologic toxicity due to gabapentin accumulation. Future studies are warranted to confirm the neurologic adverse effects of gabapentin, including any additional risks in patients with renal dysfunction.

Seizure Aggravation in Idiopathic Generalized Epilepsies

Seizures in the idiopathic generalized epilepsies (IGEs) usually remit completely with antiepileptic drugs (AEDs). Occasionally, however, they may be aggravated by AEDs. Before attributing exacerbation of seizures to an AED, alternative explanations need to be excluded. These include natural fluctuation of seizures, irregular compliance, maladjustment to the disease, comorbid illness, and development of tolerance. Aggravation may be due to a paradoxical reaction or drug-induced encephalopathy, sedative effects, or inappropriate use of a drug; and this need to be established, as it will guide management. An important caveat is that most data on aggravation of generalized seizures are based on anecdotal case reports or case series. Whether considering efficacy or aggravation, the interpretation of data from uncontrolled studies and case reports must be treated with caution. In practice, despite the fact that clear evidence is lacking, the possibility of seizure aggravation must be considered when treating people with IGEs. Predictive factors for seizure aggravation in a particular patient with a specific drug are yet to be fully defined. It is paramount to classify seizure type correctly in all patients. If this is not possible, a broad-spectrum AED should be used. Drugs that modulate Na+-channels and GABAergic drugs seem to be more prone to aggravating seizures, and therefore are best avoided in the initial management of IGE. Further studies are required to elucidate this phenomenon in full. It is interesting to speculate that paradoxical responses to AEDs may have pharmacogenetic value, serving as tools for a more precise and useful characterization of the epilepsies.

Evidence-based Treatment of Idiopathic Generalized Epilepsies with New Antiepileptic Drugs

With the introduction of over ten new antiepileptic drugs (AEDs) since 1993, the hope has been that at least some of these agents would be useful for not just partial seizures, but also for the primary generalized seizures of the idiopathic generalized epilepsies (IGE). The development of evidence-based treatment guidelines in the IGE, however, faces a number of challenges, particularly after an antiepileptic drug (AED) receives approval for one indication. The majority of patients with IGE are controlled with first-line therapy if appropriately selected. Case reports or series typically appear with use in refractory patients, but these studies lack the rigor to allow formulation of guidelines. Still we are beginning to see some good class I and II data to support use of selected second-generation AEDs. It is postulated that lamotrigine (LTG), levetiracetam (LEV), topiramate (TPM), and zonisamide (ZSM) may have efficacy for a broad spectrum of seizure types including those of IGE. At the present time good class I and II evidence exists to support the use of LTG for typical absence, LEV for idiopathic myoclonic seizures, and TPM for primary generalized tonic-clonic seizures, even though only TPM has FDA approval for primary generalized seizures. This article examines the available rigorous evidence that can support these uses and also discusses some selected other reports that suggest a spectrum of efficacy for these new agents.

Aggravation of epilepsy by antiepileptic drugs

Antiepileptic drugs may paradoxically worsen seizure frequency or induce new seizure types in some patients with epilepsy. The mechanisms of seizure aggravation by antiepileptic drugs are mostly unknown and may be related to specific pharmacodynamic properties of these drugs. This article provides a review of the various clinical circumstances of seizure exacerbation and aggravation of epilepsy by antiepileptic drugs as well as a discussion of possible mechanisms underlying the occasional paradoxical effect of these drugs. Antiepileptic drug-induced seizure aggravation can occur virtually with all antiepileptic medications. Drugs that aggravate seizures are more likely to have only one or two mechanisms of action, either enhanced gamma-aminobutyric acid-mediated transmission or blockade of voltage-gated sodium channels. Antiepileptic drug-induced seizure exacerbation should be considered and the accuracy of diagnosis of the seizure type should be questioned whenever there is seizure worsening or the appearance of new seizure types after the introduction of any antiepileptic medication.

Dystonia Induced by Gabapentin

OBJECTIVE:

To report a case of dystonia as an adverse effect of gabapentin.

CASE SUMMARY:

A 72-year-old woman was diagnosed with essential tremor and treated with propranolol 120 mg daily. The drug was withdrawn because of bradycardia, and gabapentin was prescribed 3 times a day at escalating doses to reach 2100 mg daily. The woman developed a dystonic reaction involving muscles of the neck and both arms that resolved rapidly after drug withdrawal. She was restarted on gabapentin with slow titration to 1800 mg daily, but the same dystonic reaction appeared, which led to definitive withdrawal of the drug. An objective causality assessment revealed that this adverse effect was highly probable.

DISCUSSION:

There have been only a few previous reports of gabapentin-induced dystonia. Other movement disorders reported with gabapentin include myoclonus, ataxia, and choreoathetosis. Gabapentin has been used to treat dystonias with variable results.

CONCLUSIONS:

Although gabapentin is widely used and well tolerated, it can cause dystonic reactions, which are reversible after drug withdrawal.

Gabapentin-induced Myoclonus in End-stage Renal Disease

PURPOSE

We analyzed the occurrence and clinical features of myoclonus in patients with end-stage renal disease (ESRD) who were treated with gabapentin (GBP).

METHODS

We reviewed the medical records of patients with ESRD who were treated with GBP and hospitalized during an 18-month period and analyzed clinical details such as type of myoclonus, doses of GBP, electroencephalographic (EEG) findings, and relation of symptoms to GBP exposure and dosage.

RESULTS

Three of 71 patients had myoclonus with GBP doses ranging from 9 mg/kg to 20 mg/kg and within 4 months of treatment onset. Myoclonus was characterized as multifocal, involving all extremities in the three patients. EEG did not show epileptiform discharges with the myoclonus. Myoclonus resolved in the three individuals within 4-15 days after GBP was discontinued.

CONCLUSIONS

GBP increases the risk of myoclonus in ESRD. Myoclonus in these individuals was more disabling than that in patients with normal renal function, and discontinuation of GBP is required to restore normal function.

Benign febrile myoclonus in childhood

BACKGROUND

Myoclonus is often associated with progressive myoclonic epilepsy or neurodegenerative conditions. Febrile myoclonus is a benign phenomenon, which has only been reported previously in one child.

METHODS

The clinical features of three children with fever-induced myoclonus are described.

RESULTS

Fever-induced myoclonus is characterized by frequent myoclonus, which resolves with resolution of the fever in otherwise healthy children.

CONCLUSIONS

Recognition of fever-induced myoclonus as a benign phenomenon may prevent unnecessary investigations and interventions.

Worsening of Seizures by Oxcarbazepine in Juvenile Idiopathic Generalized Epilepsies

PURPOSE

Several studies have shown that carbamazepine (CBZ) may aggravate idiopathic generalized epilepsy (IGE). Oxcarbazepine (OXC) is a new drug chemically related to CBZ. We report six cases of juvenile IGE with a clear aggravation by OXC.

METHODS

We retrospectively studied all patients with IGE first referred to our epilepsy department between January 2001 and June 2003 and treated with OXC.

RESULTS

During this period, six patients were identified. All had an aggravation of their epilepsy in both clinical and EEG activities. OXC had been used because of an incorrect diagnosis of focal epilepsy or generalized tonic-clonic seizures (GTCSs) of undetermined origin (no syndromic classification of the epilepsy). Before OXC, only one patient had experienced a worsening of seizures with an inadequate drug (CBZ). Four had juvenile myoclonic epilepsy, one had juvenile absence epilepsy, and one had IGE that could not be classified into a precise syndrome. OXC (dosage range, 300-1,200 mg/day) was used in monotherapy in all of them except for one patient. Aggravation consisted of a clear aggravation of myoclonic jerks (five cases) or de novo myoclonic jerks (one case). Three patients had exacerbation of absence seizures. One patient had worsened dramatically and had absence status, and one had de novo absences after OXC treatment. The effects of OXC on GTCSs were less dramatic, with no worsening in frequency in three and a slight increase in three.

CONCLUSIONS

OXC can be added to the list of antiepileptic drugs that can exacerbate myoclonic and absence seizures in IGE.