Myopathies in the intensive care unit

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.

Advances in the epidemiology, pathogenesis, and management of Cushing's syndrome complications

Cushing's syndrome (CS) is a clinical condition resulting from chronic exposure to glucocorticoid excess. As a consequence, hypercortisolism contributes significantly to the early development of systemic disorders by direct and/or indirect effects. Complications such as obesity, hypertension, diabetes, dyslipidemia, and hypercoagulability cause premature atherosclerosis and increase cardiovascular mortality. Impairment of the skeletal system is a relevant cause of morbidity and disability in these patients especially due to the high prevalence of vertebral fractures. In addition, muscle weakness, emotional lability, depression, and impairment of quality of life are very common. Clinical management of these patients is complex and should be particularly careful in identifying global cardiovascular risks and aim at controlling all complications. Although the primary goal in the prevention and treatment of complications is the correction of hypercortisolism, treatment does not completely eliminate these comorbidities. Given that cardiovascular risk and fracture risk can persist after cure, early detection of each morbidity could prevent the development of irreversible damage. In this review we present the various complications of CS and their pathogenetic mechanisms. We also suggest the clinical management of these patients based on our extensive clinical experience and on the available literature.

Glucocorticoid-induced myopathy

Glucocorticoid-induced myopathy, characterized by muscle weakness without pain, fatigue and atrophy, is an adverse effect of glucocorticoid use and is the most common type of drug-induced myopathy. This muscle disturbance has a frequency of 60%, and it has been most often associated with fluorinated glucocorticoid preparations. Glucocorticoids have a direct catabolic effect on muscle, decreasing protein synthesis and increasing the rate of protein catabolism leading to muscle atrophy. In clinical practice, it is important to differentiate myopathy due to glucocorticoid from muscle inflammatory diseases. The treatment is based on reduction or, if possible, on discontinuation of the steroid. Fluorinated glucocorticoids such as dexamethasone should be replaced with nonfluorinated glucocorticoids such as prednisone. Other experimental treatments may be tried such as IGF-I, branched-chain amino acids, creatine, androgens such as testosterone, nandrolone and dehydroepiandrosterone (DHEA), and glutamine.

Drug-induced myopathy and neuropathy

We review the drugs that are known to induce muscle and/or nerve toxicity, describe the commonly encountered signs and symptoms, and discuss the mechanisms believed to be behind these iatrogenic effects. The diagnostic approach to patients suspected of having drug-induced neuromuscular disorders includes a comprehensive history and physical examination, proper blood workup, electrophysiological studies, and, if necessary, muscle or nerve biopsy. A lot of controversial issues continue to prevail when reviewing such a topic, secondary to the greatly variable levels of certainty for the association between drugs and their neuromuscular toxicity. We focus on drugs that are proven to cause these adverse effects, with less emphasis on the anecdotally suspected agents for which coincidence has not been eliminated.

The effects of toxins on muscle

Substances known to be myotoxic are reviewed, including descriptions of the resultant clinical syndromes and the mechanisms important in their development. Certain host characteristics such as altered immune and metabolic regulation are known to modulate the effects of individual myotoxins, producing varied clinical syndromes. Evaluation procedures important in identifying a toxin-induced myopathy are described.

Endocrine myopathies

This article provides a review of some of the muscular disorders that can arise from some of the commonly seen endocrinologic disturbances. Thyroid, parathyroid, and adrenal dysfunctions as they relate to neuromuscular symptoms are discussed. Common clinical presentations of the endocrine myopathies are highlighted, along with diagnostic evaluation and treatments.