Toxic myopathies

Amiodarone-induced muscle tremor in an elderly patient: A case report

BACKGROUND

Amiodarone is a Class III antiarrhythmic drug, which has been adopted for the treatment of atrial fibrillation and ventricular arrhythmia. However, the use of amiodarone can cause lower limb muscle tremors, which is recognized as a rare side effect of this medication.

CASE SUMMARY

An 84-year-old female was administrated with amiodarone for paroxysmal supraventricular tachycardia and frequent ventricular tachycardia. The patient developed a bilateral gastrocnemius tremor in the course of medication, and the strength of the patient’s bilateral knee flexor and extensor reached 4/5 and 3/5, respectively. After the use of amiodarone was stopped, and the patient was given a small dose of levetiracetam, the lower limb tremor symptoms were significantly mitigated, along with activity and function.

CONCLUSION

Attention should be paid to the significance of the side effects of drugs in the elderly, which may be atypical in the elderly. The relevant side effects of drugs may not be as rare as reported due to individual differences and different pharmacokinetics. If the side effects are generated, the medication should be adjusted in time, and the progress of the side effects should be intervened.

Cholesterol Management in Neurology: Time for Revised Strategies?

Statin therapy has been extensively evaluated and shown to reduce the incidence of new or recurrent vascular events, ischemic stroke included. As a consequence, each published guideline pushes for lower low-density cholesterol levels in the population at large, recommending increased statin doses and/or adding new cholesterol-lowering molecules. Neurologists find it sometimes difficult to apply these guidelines, having to confront situations such as (1) ischemic strokes, mainly cardioembolic ones, in patients with already low LDL-cholesterol levels; (2) myasthenic patients, whose lifespan has been extended by available treatment, and whose age and cholesterol levels put them at risk for ischemic stroke; (3) patients with myotonic dystrophy, whose disease often associates diabetes mellitus and heart conduction defects, and in whom blood cholesterol management is also not settled. As such, further trials are needed to address these issues.

Is it really myositis? Mimics and pitfalls

Idiopathic inflammatory myopathies are a heterogeneous set of systemic inflammatory disorders primarily affecting muscle. Signs and symptoms vary greatly between and within subtypes, requiring supportive laboratory and pathologic evidence to confirm the diagnosis. Several studies are typical assessments for patients with suspected inflammatory myopathy, including muscle enzymes, autoimmune markers, imaging, and muscle biopsy. Misdiagnoses of myositis are not only related to the overlap of clinical phenotype with non-inflammatory myopathies, but also due to the limitations of diagnostic tests employed. Since many of the investigative tests are non-specific, they share features with other disorders, including muscular dystrophies, endocrine, toxic, and metabolic myopathies, and other neuromuscular or rheumatologic conditions. Recognizing the limitations of tests and understanding the shared features between inflammatory and non-inflammatory myopathies can help prevent misdiagnosing myositis with one of its several mimics.

Typical and atypical properties of peripheral nerve allografts enable novel strategies to repair segmental-loss injuries

We review data showing that peripheral nerve injuries (PNIs) that involve the loss of a nerve segment are the most common type of traumatic injury to nervous systems. Segmental-loss PNIs have a poor prognosis compared to other injuries, especially when one or more mixed motor/sensory nerves are involved and are typically the major source of disability associated with extremities that have sustained other injuries. Relatively little progress has been made, since the treatment of segmental loss PNIs with cable autografts that are currently the gold standard for repair has slow and incomplete (often non-existent) functional recovery. Viable peripheral nerve allografts (PNAs) to repair segmental-loss PNIs have not been experimentally or clinically useful due to their immunological rejection, Wallerian degeneration (WD) of anucleate donor graft and distal host axons, and slow regeneration of host axons, leading to delayed re-innervation and producing atrophy or degeneration of distal target tissues. However, two significant advances have recently been made using viable PNAs to repair segmental-loss PNIs: (1) hydrogel release of Treg cells that reduce the immunological response and (2) PEG-fusion of donor PNAs that reduce the immune response, reduce and/or suppress much WD, immediately restore axonal conduction across the donor graft and re-innervate many target tissues, and restore much voluntary behavioral functions within weeks, sometimes to levels approaching that of uninjured nerves. We review the rather sparse cellular/biochemical data for rejection of conventional PNAs and their acceptance following Treg hydrogel and PEG-fusion of PNAs, as well as cellular and systemic data for their acceptance and remarkable behavioral recovery in the absence of tissue matching or immune suppression. We also review typical and atypical characteristics of PNAs compared with other types of tissue or organ allografts, problems and potential solutions for PNA use and storage, clinical implications and commercial availability of PNAs, and future possibilities for PNAs to repair segmental-loss PNIs.

[Neurological symptoms associated with cancer treatment]

Die onkologische Behandlung ist biomarkerbasierter, molekular maßgeschneiderter und effektiver geworden. Aufbauend auf der zunehmenden Entschlüsselung zellbiologischer und molekularer Mechanismen steigt auch die Zahl zielgerichteter medikamentöser Therapien. Es steigt zudem die Zahl der Langzeitüberlebenden. Eine neuro(onko)logische Betreuung wird immer wichtiger, nicht nur wegen vermehrter direkter tumorbedingter Symptome – wie etwa der höheren Inzidenz einer Metastasierung in das Zentralnervensystem –, sondern weil im Zuge dieser modernen onkologischen systemischen Therapieformen ein breites Spektrum therapieassoziierter neurologischer Symptome auftritt, die einer sorgfältigen und raschen neurologischen/neuroonkologischen Evaluation und Therapiekonzeption bedürfen. Das Ziel dieses Artikels ist es, das Bewusstsein für die häufigsten therapieassoziierten neurologischen Symptome zu schärfen.

Drug-induced Myopathies

Differential diagnosis of muscle pain and weakness is extensive, including neurological, vertebral, arthrogenic, vascular, traumatic, immunological, endocrine, genetic and infectious aetiologies, as well as medication or toxin-related causes. Muscles are highly sensitive to a large number of drugs, especially with high doses. Although many drug classes can cause toxic myopathy, a significant number of cases are caused by lipid-lowering drugs, long-term use of corticosteroids, and, most often, alcohol misuse. Some drug interactions, e.g. those that are metabolised via the enzyme CYP3A4, can increase the serum levels of the drugs and drug-induced toxicity. A careful history of patient's drug and alcohol consumption is therefore vital. Clinical symptoms depend on the drug, dosage and patient's sensitivity. They can vary from asymptomatic increase in serum levels of creatine kinase, mild myalgia and cramps to muscle weakness, rhabdomyolysis, kidney failure and even death. The pathogenesis is often only partially known and multifactorial. Toxic myopathy is often reversible once the drug is discontinued, alternative drug therapy is started or a different dosage regimen is chosen. Complications such as acute kidney failure must be avoided, and analgesic therapy may be indicated.

Progressive increases in creatine kinase activity in an anorexic cat with necrotising myopathy

Case summary

A 5-year-old castrated male domestic shorthair cat with weight loss and reduced appetite was evaluated for increased and progressively rising creatine kinase (CK) activity. The cat had recently been diagnosed with hepatic lipidosis. Muscle biopsy and histopathology revealed mild myonecrosis and phagocytosis without obvious inflammatory cell infiltrates. Resolution of necrotising myopathy was observed after a short course of anti-inflammatory prednisolone and nutritional supplementation.

Relevance and novel information

This is the first report of a necrotising myopathy in a cat associated with progressively increasing CK activity and decreased appetite. Anorexia in cats has been associated with increased CK activity, but an underlying cause of this CK elevation has only been postulated. Here we document muscle necrosis and muscle stiffness in a cat with anorexia.

Amiodarone-induced neuromyopathy in a geriatric patient

Amiodarone is an antiarrhythmic medication with many side effects. Neuromyopathy is a rare adverse effect. We present an 87-year-old woman with bilateral leg pain and weakness in the context of amiodarone. She was admitted to the Acute Geriatric Unit in Calgary, Alberta, Canada. On examination, hip flexor and extensor strength were 2/5 bilaterally while knee flexor and extensor strength were 4/5 and 3/5, respectively. Creatine kinase and C-reactive protein levels were normal. MRI of the lumbar spine showed mild central canal stenosis. Electromyography and nerve conduction testing showed a severe axonal length-dependent polyneuropathy of the left lower extremity. There was evidence of myopathic changes to the left iliopsoas muscle. Overall, a neuromyopathic process affecting the lower extremities was supported. After discontinuation of amiodarone, mobility and function significantly improved. Although a rare complication of amiodarone, neuromyopathy should be considered in patients with compatible symptomatology.

Imatinib and Dasatinib Provoke Mitochondrial Dysfunction Leading to Oxidative Stress in C2C12 Myotubes and Human RD Cells

Tyrosine kinase inhibitors (TKIs) can cause skeletal muscle toxicity in patients, but the underlying mechanisms are mostly unclear. The goal of the current study was to better characterize the role of mitochondria in TKI-associated myotoxicity. We exposed C2C12 murine myoblasts and myotubes as well as human rhabdomyosarcoma cells (RD cells) for 24 h to imatinib (1–100 µM), erlotinib (1–20 µM), and dasatinib (0.001–100 µM). In C2C12 myoblasts, imatinib was membrane toxic at 50 µM and depleted the cellular ATP pool at 20 µM. In C2C12 myotubes exposed to imatinib, ATP depletion started at 50 µM whereas membrane toxicity was not detectable. In myoblasts and myotubes exposed to dasatinib, membrane toxicity started at 0.5 µM and 2 µM, respectively, and the ATP drop was visible at 0.1 µM and 0.2 µM, respectively. When RD cells were exposed to imatinib, ATP depletion started at 20 µM whereas membrane toxicity was not detectable. Dasatinib was membrane toxic at 20 µM and depleted the cellular ATP pool already at 0.5 µM. Erlotinib was not toxic in both cell models. Imatinib (20 µM) and dasatinib (1 µM) reduced complex I activity in both cell models. Moreover, the mitochondrial membrane potential (Δψm) was dissipated for both TKIs in myotubes. In RD cells, the Δψm was reduced only by dasatinib. Both TKIs increased mitochondrial superoxide accumulation and decreased the mitochondrial copy number in both cell lines. In consequence, they increased protein expression of superoxide dismutase (SOD) 2 and thioredoxin 2 and cleavage of caspase 3, indicating apoptosis in C2C12 myotubes. Moreover, in both cell models, the mRNA expression of Sod1 and Sod2 increased when RD cells were exposed to dasatinib. Furthermore, dasatinib increased the mRNA expression of atrogin-1 and murf-1, which are important transcription factors involved in muscle atrophy. The mRNA expression of atrogin-1 increased also in RD cells exposed to imatinib. In conclusion, imatinib and dasatinib are mitochondrial toxicants in mouse C2C12 myotubes and human RD cells. Mitochondrial superoxide accumulation induced by these two TKIs is due to the inhibition of complex I and is probably related to impaired mitochondrial and myocyte proliferation.

Approach to Muscle and Neuromuscular Junction Disorders

PURPOSE OF REVIEW

Muscle and neuromuscular junction disorders are a diverse group of disorders that can be difficult to diagnose. This article provides a diagnostic approach based on clinical history and neurologic examination leading to a narrow set of diagnostic tests.

RECENT FINDINGS

Numerous discoveries in recent years have facilitated clinician access to more advanced laboratory and genetic testing to pinpoint the exact diagnosis in patients with muscle or neuromuscular junction disorders. Large-scale genetic testing has become much less expensive, and free testing has become available for many of the rare conditions because of increased research and the availability of effective therapies for these rare disorders.

SUMMARY

The approach to muscle and neuromuscular junction disorders depends on the clinical pattern of muscle weakness. By classifying patients into one of 10 muscle patterns, diagnostic testing can be targeted and gene testing yield will be optimized. With the increased accessibility and reduced cost of genetic testing (eg, gene panels, whole-exome sequencing, whole-genome sequencing, and chromosomal microarray), this clinical approach to muscle weakness and targeted gene testing will ensure a cost-effective investigational plan. This clinical approach should also assist clinicians in making a timely and accurate diagnosis.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

[Treatment-associated neurological symptoms of cancer patients and their treatment]

With the increasing understanding of the specific molecular and cellular pathogenesis of cancer, systemic cancer treatment has become much more targeted and in part substantially more effective. The increased number of long-term survivors and the number of highly specific targeted therapies have resulted in a wide range of neurological complications. Neurologists are increasingly confronted with previously unknown neurological complications of cancer treatment. A profound understanding of the molecular and cellular mechanisms of action of anticancer drugs is the key for a prompt diagnosis and appropriate treatment of these treatment-associated neurological complications.

Diagnostic Imaging of Inflammatory Myopathies: New Concepts and a Radiological Approach

PURPOSE OF REVIEW

The purpose of this review article is to highlight the current role of diagnostic imaging in the assessment of inflammatory myopathies.

RECENT FINDINGS

Recent research demonstrates that imaging plays an important role in evaluating patients with symptoms of an inflammatory myopathy. In general, MRI is the pivotal imaging modality for assessing inflammatory myopathies, revealing precise anatomic details because of changes in the signal intensity of the muscles. Whole-body MR imaging has become increasingly important over the last several years. US is also a valuable imaging modality for scanning muscles. Together with the clinical history, familiarity with the imaging features of inflammatory myopathies is essential for formulating an accurate diagnosis.