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

The Spontaneous Incidence of Neurological Clinical Signs in Preclinical Species Using Cage-side Observations or High-definition Video Monitoring: A Retrospective Analysis

When conducting toxicology studies, the interpretation of drug-related neurological clinical signs such as convulsions, myoclonus/myoclonic jerks, tremors, ataxia, and salivation requires an understanding of the spontaneous incidence of those observations in commonly used laboratory animal species. The spontaneous incidence of central nervous system clinical signs in control animals from a single facility using cage-side observations or high definition video monitoring was retrospectively analyzed. Spontaneous convulsions were observed at low incidence in Beagle dogs and Sprague-Dawley rats but were not identified in cynomolgus monkeys and Göttingen minipigs. Spontaneous myoclonic jerks and muscle twitches were observed at low incidence in Beagle dogs, cynomolgus monkeys, and Sprague-Dawley rats but were not seen in Göttingen minipigs. Spontaneous ataxia/incoordination was identified in all species and generally with a higher incidence when using video monitoring. Salivation and tremors were the two most frequent spontaneous clinical signs and both were observed in all species. Data from the current study unveil potential limitations when using control data obtained from a single study for toxicology interpretation related to low incidence neurological clinical signs while providing historical control data from Beagle dogs, cynomolgus monkeys, Sprague-Dawley rats, and Göttingen minipigs.

Amantadine-Induced Craniofacial Myoclonus: Distinctive Iatrogenic Dysarthria in Parkinson's Disease

Background

Amantadine is a widely prescribed medication in Parkinson's disease (PD). A distinctive craniofacial distribution of myoclonus with speech impairment is an underrecognized iatrogenic complication in amantadine-treated patients with PD.

Cases

We report 7 patients with idiopathic PD (disease duration, 6-21 years) who developed speech-induced craniofacial-predominant myoclonus with "stuttering-like" dysarthria and speech arrests days to months after amantadine initiation or dose increase. Renal insufficiency was identified as a risk factor in 4 cases. In all cases, reduction or discontinuation of amantadine markedly attenuated the myoclonus and restored speech intelligibility.

Literature Review

Amantadine can induce subcortical segmental or generalized myoclonus. A report in 1996 of "vocal myoclonus" in an amantadine-treated patient with PD was the first observation of a focal distribution of myoclonus, particularly affecting speech. Since then, few cases of craniofacial myoclonus with speech impairment have been reported, none with accompanying video. With 1 exception, the craniofacial distribution was part of a generalized pattern of amantadine-induced myoclonus. Comorbid renal insufficiency is a recognized risk factor.

Conclusions

Speech-induced craniofacial myoclonus, with marked "stuttering-like" dysarthria and speech arrests, is a disabling iatrogenic complication in PD that resolves upon amantadine discontinuation.

Myoclonus Secondary to Amantadine: Case Report and Literature Review

The usual adverse events of amantadine are dizziness, dry mouth, and peripheral edema. Postmarketing experience has revealed abnormal movements such as tremors, involuntary muscle contractions, and gait abnormalities. Herein, we report a case of an elderly male who presented with generalized twitching associated with amantadine. A 64-year-old male presenting with jerking movements within one day of onset was admitted. Sudden and involuntary distal lower and upper limb muscle twitching was observed. The subject presented subsequent brief movements when attempting to stand or hold arms antigravity. He was diagnosed with Parkinson's disease three years ago. Eight days before the presentation to the emergency department, he consulted with his primary care physician, who prescribed amantadine to improve his motor symptoms. On the seventh day, he developed brisk abnormal movements. Laboratory exams, neuroimaging, and electroencephalogram were unremarkable. Amantadine was discontinued. After three days, the patient reported that his jerking movements had fully recovered. To the authors' knowledge, 22 individuals with amantadine-associated myoclonus had already been reported in the literature. The pathophysiology of amantadine-induced myoclonus is probably related to serotoninergic pathways. Myoclonus secondary to amantadine was slightly more common in men. The population affected was elderly, with a mean and median age of 67.7 and 64 years.

Tackling seizures in patients with Alzheimer's disease

INTRODUCTION

In past years, a possible bidirectional link between epilepsy and Alzheimer's disease (AD) has been proposed: if AD patients are more likely to develop epilepsy, people with late-onset epilepsy evidence an increased risk of dementia. Furthermore, current research suggested that subclinical epileptiform discharges may be more frequent in patients with AD and network hyperexcitability may hasten cognitive impairment.

AREAS COVERED

In this narrative review, the authors discuss the recent evidence linking AD and epilepsy as well as seizures semeiology and epileptiform activity observed in patients with AD. Finally, anti-seizure medications (ASMs) and therapeutic trials to tackle seizures and network hyperexcitability in this clinical scenario have been summarized.

EXPERT OPINION

There is growing experimental evidence demonstrating a strong connection between seizures, neuronal hyperexcitability, and AD. Epilepsy in AD has shown a good response to ASMs both at the late and prodromal stages. The new generation ASMs with fewer cognitive adverse effects seem to be a preferable option. Data on the possible effects of network hyperexcitability and ASMs on AD progression are still inconclusive. Further clinical trials are mandatory to identify clear guidelines about treatment of subclinical epileptiform discharges in patients with AD without seizures.

Treatable Hyperkinetic Movement Disorders Not to Be Missed

Hyperkinetic movement disorders are characterized by the presence of abnormal involuntary movements, comprising most notably dystonia, chorea, myoclonus, and tremor. Possible causes are numerous, including autoimmune disorders, infections of the central nervous system, metabolic disturbances, genetic diseases, drug-related causes and functional disorders, making the diagnostic process difficult for clinicians. Some diagnoses may be delayed without serious consequences, but diagnosis delays may prove detrimental in treatable disorders, ranging from functional disabilities, as in dopa-responsive dystonia, to death, as in Whipple's disease. In this review, we focus on treatable disorders that may present with prominent hyperkinetic movement disorders.

Amantadine Associated Myoclonus: Case Report and Review of the Literature

PURPOSE

Amantadine is commonly used to treat Parkinson's disease. A case of myoclonus and asterixis was associated with amantadine is reported.

CASE SUMMARY

An 80-year-old man with Parkinson's disease diagnosed in 2015 was started on amantadine for treatment of progressive tremor and orofacial dyskinesias induced by levodopa. He took amantadine 100mg orally daily for 7 days, then increased to 100mg twice a day thereafter. The patient complained of "worsening tremor" after 9 days and amantadine was decreased to 100mg daily. After 1 month on this dose, the patient reported that his "tremor" persisted and experienced visual hallucinations. His examination demonstrated diffuse myoclonus throughout his extremities and trunk, as well as asterixis when attempting to stand or holding his arms antigravity. Laboratory testing for renal and hepatic failure was unrevealing. Amantadine was reduced to 50mg daily for 4 days and then discontinued. Myoclonus resolved 3 days after discontinuation of amantadine.

CONCLUSION

While amantadine-induced myoclonus is rare, health care providers should be vigilant in monitoring for signs and symptoms of myoclonus following amantadine initiation.

Assessment of Extrapyramidal Symptoms Associated with Psychotropics Pharmacological Treatments, and Associated Risk Factors

BACKGROUND

Extrapyramidal Symptoms (EPS) are unwanted symptoms commonly originating from the use of certain medications. The symptoms can range from minimal discomfort to permanent involuntary muscular movements. The aims of the study were to examine the incidence of drug-induced extrapyramidal symptoms (di-EPS), associated risk factors, and clinical characteristics.

METHODS

This is a retrospective, observational study of di-EPS conducted in outpatient clinics of Jordan using the longitudinal health database (Hakeem®) for data collection. Patients who received drugs with the risk of EPS during the period 2010-2020 were included and followed. Patients with any of the known underlying conditions that may cause EPS or were currently taking drugs that may mask the symptoms were excluded. Gender and age-matched control subjects were included in the study. The Statistical Package for Social Science (SPSS®) version 26 was used for data analysis.

RESULTS

The final dataset included 34898 exposed patients and 69796 matched controls. The incidence of di-EPS ranged from 9.8% [Amitriptyline 25mg] to 28.9% (Imipramine 25mg). Baseline factors associated with a significantly higher risk of developing di-EPS were age {HR: 1.1 [95%CI: 0.8-1.2, p=0.003], smoking {HR: 1.7 (95%CI: 1.3-2.2), p=0.02}, tremor history {HR: 7.4 (95%CI: 5.9-8.3), p=.002} and history of taking antipsychotics {HR: 3.9, (95% CI: 2.5-4.6), p=0.001}. Patients taking paroxetine {HR: 8.6 [95%CI: 7.4-9.8], p=.0002},imipramine {HR: 8.3, [7.1-10.5], p=0.01}, or fluoxetine {HR: 8.2 (95%CI: 6.8-9.3), p=.006} had a significantly higher risk of developing di-EPS compared to patients taking citalopram. Myoclonus, blepharospasm, symptoms of the basal ganglia dysfunction, and organic writers' cramp were reported among participants.

CONCLUSION

Patients treated with paroxetine, imipramine, fluoxetine, or clomipramine had a higher risk of developing di-EPS than patients treated with citalopram. The difference in gender was not significantly related to di-EPS development. Whereas age, smoking, and history of taking antipsychotics were significantly associated with di-EPS development.

KEY FINDINGS

• High incidence of drug-induced extrapyramidal symptoms (di-EPS) was reported• Age, smoking, tremor history, and history of taking antipsychotics were risk factors of drug-induced extrapyramidal symptoms.• Patients taking paroxetine, imipramine or fluoxetine had a significantly higher risk of developing di-EPS compared to patients taking citalopram.

Myoclonus induced by amoxicillin-clavulanic acid

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We present a patient in whom myoclonus appeared after initiation of treatment with amoxicillin-clavulanic acid.

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Myoclonus and EEG abnormalities disappeared after discontinuation of antibiotic treatment.

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This possible adverse effect should be considered to avoid performing aggressive therapeutic maneuvers.

Iatrogenesis and neurological manifestations in the elderly

Older people are often exposed to polypharmacy in a multimorbidity context. Inappropriate polypharmacy is often harmful, increasing the risk of inappropriate prescriptions and therefore adverse drug events (ADEs). Five to 20% of all hospital admissions are related to ADE in older people, among which 40 to 70% could be prevented. However, identifying ADEs and drug-related admissions in the elderly is challenging because ADEs often present as common geriatric problems such as falls, delirium, which might be due to the aging process, underlying diseases, and/or medications. In the pharmacovigilance database of the World Health Organization, drug-related neurological manifestations are the third reported cause of ADEs in the elderly, and neurological drugs are the third leading class of medications involved in ADEs. We must therefore be particularly vigilant, both in our prescriptions but also in our diagnoses to avoid prescribing inappropriate treatments and detect ADEs. Even though multiple pharmacologic changes occur in the elderly (absorption, distribution, drug metabolism and excretion), most of medications are still often prescribed at the same daily dosage as in young adults. When prescribing any drug for old patients, we should remember that daily intake should be adapted to these specificities, keeping in mind the old well-known aphorism "start low, go slow". In this review, we describe the main drug-related neurological manifestations (drug-induced movement disorders, falls, seizures, delirium, hypoglycemia, stroke, hyponatremia, peripheral neuropathy and myopathy, and serotonin syndrome) and the main drugs associated with neurological manifestations (dopamine receptor blocking agents, antithrombotics, anticholinergics, beta-lactams, antidepressants, benzodiazepines, mood stabilizers).

Pediatric Iatrogenic Movement Disorders

The acute development of a movement disorder is often a dramatic and frightening experience for patients and families, often requiring urgent or emergent evaluation by a neurologist. In the assessment of these patients, one relies on the history, physical and neurologic examination to determine the etiology of the condition. We aim to demonstrate that a thorough medication history is an incredibly critical part of this evaluation as iatrogenic movement disorders can arise from exposure not only to psychoactive medications, but from drugs prescribed for a variety of nonneurologic disorders. This comprehensive review is organized by movement disorder semiology so that the reader can more readily develop a differential diagnosis when evaluating a patient with a movement disorder.

Myoclonic Disorders

Few movement disorders seem to make a straightforward approach to diagnosis and treatment more difficult and frustrating than myoclonus, due to its plethora of causes and its variable classifications. Nevertheless, in recent years, exciting advances have been made in the elucidation of the pathophysiology and genetic basis of many disorders presenting with myoclonus. Here, we provide a review of all of the important types of myoclonus encountered in pediatric and adult neurology, with an emphasis on the recent developments that have led to a deeper understanding of this intriguing phenomenon. An up-to-date list of the genetic basis of all major myoclonic disorders is presented. Randomized studies are scarce in myoclonus therapy, but helpful pragmatic approaches at diagnosis as well as treatment have been recently suggested.