Truncal ataxia in chronic anticonvulsant treatment. Association with drug-induced folate deficiency

Overview of Movement Disorders Secondary to Drugs

Drug-induced movement disorders affect a significant percentage of individuals, and they are commonly overlooked and underdiagnosed in clinical practice. Many comorbidities can affect these individuals, making the diagnosis even more challenging. Several variables, including genetics, environmental factors, and aging, can play a role in the pathophysiology of these conditions. The Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Statistical Classification of Diseases and Related Health Problems (ICD) are the most commonly used classification systems in categorizing drug-induced movement disorders. This literature review aims to describe the abnormal movements associated with some medications and illicit drugs. Myoclonus is probably the most poorly described movement disorder, in which most of the reports do not describe electrodiagnostic studies. Therefore, the information available is insufficient for the diagnosis of the neuroanatomical source of myoclonus. Drug-induced parkinsonism is rarely adequately evaluated but should be assessed with radiotracers when these techniques are available. Tardive dyskinesias and dyskinesias encompass various abnormal movements, including chorea, athetosis, and ballism. Some authors include a temporal relationship to define tardive syndromes for other movement disorders, such as dystonia, tremor, and ataxia. Antiseizure medications and antipsychotics are among the most thoroughly described drug classes associated with 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.

Can Therapeutic-Range Chronic Phenytoin Administration Cause Cerebellar Ataxia?

Phenytoin (PHT) is a first line antiepileptic drug (AED) used to treat many epilepsy syndromes. As with other AEDs, there are various adverse effects associated with PHT. For this brief review, we searched for evidence of cerebellar ataxia as a chronic adverse effect of therapeutic-range PHT treatment. Many previous studies appeared related to this issue, but many of those studies were designed to resolve questions related to the persistent residual effects of toxic-range PHT therapy, or they were inconclusive due to an absence of critical information such as PHT serum concentration, cerebellar symptoms/signs, and other factors contributing to cerebellar degeneration. Nevertheless, there were a few reports suggesting that cerebellar ataxia may be a chronic adverse effect of therapeutic-range PHT therapy and that a possible pathomechanism for that effect is folate deficiency. Moreover, there is the possibility that there may be patient-specific susceptibility factors affecting ataxia. Further studies are needed to elucidate the incidence, risk factors, and pathomechanism of cerebellar ataxia as a chronic adverse effect of therapeutic-range PHT treatment.

Pharmacological and neuroethological studies of three antiepileptic drugs in the Genetic Audiogenic Seizure Hamster (GASH:Sal)

Epilepsy modeling is essential for understanding the basic mechanisms of the epileptic process. The Genetic Audiogenic Seizure Hamster (GASH:Sal) exhibits generalized tonic-clonic seizures of genetic origin in response to sound stimulation and is currently being validated as a reliable model of epilepsy. Here, we performed a pharmacological and neuroethological study using well-known and widely used antiepileptic drugs (AEDs), including phenobarbital (PB), valproic acid (VPA), and levetiracetam (LEV). The intraperitoneal administration of PB (5-20mg/kg) and VPA (100-300mg/kg) produced a dose-dependent decrease in GASH:Sal audiogenic seizure severity scores. The administration of LEV (30-100mg/kg) did not produce a clear effect. Phenobarbital showed a short plasmatic life and had a high antiepileptic effect starting at 10mg/kg that was accompanied by ataxia. Valproic acid acted only at high concentrations and was the AED with the most ataxic effects. Levetiracetam at all doses also produced sedation and ataxia side effects. We conclude that the GASH:Sal is a reliable genetic model of epilepsy suitable to evaluate AEDs.

Balance performance in adult epilepsy patients

PURPOSE

To evaluate the magnitude of subclinical balance dysfunction in adult epilepsy patients and to assess the relative contribution of different variables to balance impairment.

METHODS

Balance performance was evaluated by computerized dynamic platform posturography (CDPP) in 25 adult patients following a generalized tonic-clonic seizure (GTCS) and in 11 healthy subjects.

RESULTS

The GTCS was a breakthrough seizure in 20 patients with epilepsy and a first seizure in 5. Seven of the patients had localization-related epilepsy and 13 had generalized epilepsy. Mean epilepsy duration was 6.6 years. Nineteen of the patients were treated with antiepileptic drugs (AEDs), 16 on monotherapy and three on polytherapy. Brain CT scan and EEG abnormalities were found in 7 and 14 patients, respectively. None of the patients had clinical signs of balance dysfunction. Postural function, measured by Sway Index (SI), was worse in the patients compared to controls. A lower SI was found in patients who did not receive AEDs, had one or two seizures, had a disease duration of less than a year and had a generalized epilepsy.

CONCLUSIONS

Although the study group was small and heterogeneous and only a small number of parameters have reached statistical significance, it seems that posturography can be helpful in the evaluation of postural stability in adult patients with epilepsy.

Antiepileptic drugs and their impact on balance

Antiepileptic drugs (AEDs) are being used with increasing frequency, not only to manage epilepsy, but also in the treatment of other conditions including neuropathic pain, migraine headaches and psychiatric conditions requiring mood stabilization. Although AEDs as a class are commonly prescribed in older patients and those with a predisposition to imbalance, the effect these drugs exert on gait and equilibrium has received very little study. Data from controlled efficacy and safety trials suggests that some AEDs are more apt to affect balance than others, even at therapeutic doses. In particular, phenytoin, primidone and phenobarbital produce more dizziness than some of the newer AEDs such as lamotrigine, levetiracetam and oxcarbazepine. For some of the other new AEDs, the data are simply not sufficient to estimate their effect on balance. This article reviews the current evidence that may guide the clinician in choosing a medication likely to have a low impact on gait and balance. Considering the risks and morbidity associated with imbalance and falls, particularly in the elderly, the direct effects of AEDs on balance should be examined further.

Case report: subacute combined degeneration of the spinal cord from folate deficiency

Subacute combined degeneration of the spinal cord is a rare neurologic complication of folate deficiency. Progressive gait disturbance, weakness, confusion, and depression developed in a 39-year-old man. He had taken phenobarbital for more than 2 years. He was bedbound, with new loss of position and vibration senses in the lower extremities. His hemoglobin was 2.9/dl, mean corpuscular volume 122 fl, vitamin B12 428 pg/ml, and folate 1 ng/ml. Peripheral blood and bone marrow showed megaloblastic anemia. Serum methylmalonic acid and homocysteine levels were consistent with folate deficiency, not B12 deficiency. Treatment with folate and packed erythrocytes resulted at 4 months in overall improvement, including walking. Position sense was restored, and vibration sense had become nearly normal. The authors found no cause for folate deficiency except phenobarbital.

Gross motor and balance impairments in children and adolescents with epilepsy

The purpose of this study was to determine the influence of age, seizure type and anticonvulsant medication protocol on balance and motor proficiency in 21 subjects with epilepsy (aged seven to 17 years) who did not have mental retardation or cerebral palsy. The Bruininks-Oseretsky balance subtest and a force platform with computer-controlled feedback of the center of force were used to evaluate balance and goal-oriented motion during static and dynamic motor tasks. These motor proficiency and balance assessments may be useful to 'unmask' deficits in motor performance associated with epilepsy, assist the evaluation of anticonvulsant side-effects, and serve as one guide for developing a comprehensive rehabilitation program.

Ataxia in institutionalized patients with epilepsy

Fifty-four per cent of 41 chronically institutionalized adult patients with epilepsy had ataxia of gait (wide mean stride width). None of the following correlated with stride width: serum phenytoin, previous phenytoin toxicity, seizure frequency, or status epilepticus. Seventeen of the 41 patients had computed tomographic head scans. Patients with radiological evidence of cerebellar atrophy had a wider mean stride width, later age of onset of seizures, greater peak serum concentrations of phenytoin than did those without cerebellar atrophy. Ataxia of gait was inconsistently associated with cerebellar atrophy. Elevated serum/plasma concentrations of phenytoin may be a risk factor for cerebellar atrophy, but seizure frequency or status epilepticus are not independently related to this complication.

Balance and cognitive impairment in two epileptic patients before and after vagal nerve stimulation

Balance and cognition were assessed in two patients with uncontrolled complex partial seizures. The patients were on anticonvulsant medications and were treated with left vagal stimulation. Balance and cognition were assessed before and after vagal stimulation, and the results were compared with age matched controls and older patients with Parkinson's disease. Severe impairments of function were found in the epileptic patients, and such negative effects of medication make vagal stimulation a potentially practical alternative treatment for uncontrolled epilepsy.