Metabolic myopathies: update 2009

A randomized trial of coenzyme Q10 in mitochondrial disorders

Case reports and open-label studies suggest that coenzyme Q(10) (CoQ(10)) treatment may have beneficial effects in mitochondrial disease patients; however, controlled trials are warranted to clinically prove its effectiveness. Thirty patients with mitochondrial cytopathy received 1200 mg/day CoQ(10) for 60 days in a randomized, double-blind, cross-over trial. Blood lactate, urinary markers of oxidative stress, body composition, activities of daily living, quality of life, forearm handgrip strength and oxygen desaturation, cycle exercise cardiorespiratory variables, and brain metabolites were measured. CoQ(10) treatment attenuated the rise in lactate after cycle ergometry, increased (∽1.93 ml) VO(2)/kg lean mass after 5 minutes of cycling (P < 0.005), and decreased gray matter choline-containing compounds (P < 0.05). Sixty days of moderate- to high-dose CoQ(10) treatment had minor effects on cycle exercise aerobic capacity and post-exercise lactate but did not affect other clinically relevant variables such as strength or resting lactate.

Necrotizing vacuolar myopathy presenting with recurrent myoglobinuria

Myoglobinuria occurs in a variety of systemic and neurological disorders and can pose diagnostic challenges. We report on a 23-year-old man in whom recurrent myoglobinuria was observed due to necrotizing vacuolar myopathy confirmed on muscle biopsy. Histopathologically the intramuscular vacuoles lacked the typical findings reported in vacuolar myopathy due to disorders of glycogen and lipid metabolism. We discuss the management approach to recurrent myoglobinuria. Recurrent myoglobinuria in the absence of toxin or drug exposure and seizure is more often due to primary muscle disease. Recognizing the presence of myoglobinuria and the proximate cause is essential in preventing the development of renal dysfunction and the future recurrence of symptoms.

Clinical and biochemical improvement of very long-chain acyl-CoA dehydrogenase deficiency in pregnancy

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an enzymatic defect of the fatty acid (FA) beta oxidation pathway. In catabolic states, such as labor and early postpartum period, patients are potentially prone to metabolic decompensation and subsequent rhabdomyolysis with increased risk for myoglobinuria and renal insufficiency. We report a 21-year-old primigravida with a previously characterized VLCAD deficiency, who experienced frequent and unprovoked episodes of rhabdomyolysis before pregnancy. As there was no published experience to guide her management, a detailed multidisciplinary care plan was established to minimize the potential morbidity. Although there is little known about the antenatal course of gravidae affected by VLCAD, we predicted that placental and fetal beta-oxidation in an unaffected pregnancy may temporize or even improve maternal FA beta-oxidation. Consistent with our prediction, we observed a significant clinical and biochemical improvement throughout her pregnancy, and she delivered vaginally with an uncomplicated postpartum course. We conclude that although VLCAD deficiency can present a therapeutic challenge during pregnancy, the beneficial placento-maternal metabolic interactions and the implementation of a proper peripartum management reassure a successful antenatal and perinatal outcome.

A diagnostic algorithm for metabolic myopathies

Metabolic myopathies comprise a clinically and etiologically diverse group of disorders caused by defects in cellular energy metabolism, including the breakdown of carbohydrates and fatty acids to generate adenosine triphosphate, predominantly through mitochondrial oxidative phosphorylation. Accordingly, the three main categories of metabolic myopathies are glycogen storage diseases, fatty acid oxidation defects, and mitochondrial disorders due to respiratory chain impairment. The wide clinical spectrum of metabolic myopathies ranges from severe infantile-onset multisystemic diseases to adult-onset isolated myopathies with exertional cramps. Diagnosing these diverse disorders often is challenging because clinical features such as recurrent myoglobinuria and exercise intolerance are common to all three types of metabolic myopathy. Nevertheless, distinct clinical manifestations are important to recognize as they can guide diagnostic testing and lead to the correct diagnosis. This article briefly reviews general clinical aspects of metabolic myopathies and highlights approaches to diagnosing the relatively more frequent subtypes (Fig. 1). Fig. 1 Clinical algorithm for patients with exercise intolerance in whom a metabolic myopathy is suspected. CK-creatine kinase; COX-cytochrome c oxidase; CPT-carnitine palmitoyl transferase; cyt b-cytochrome b; mtDNA-mitochondrial DNA; nDNA-nuclear DNA; PFK-phosphofructokinase; PGAM-phosphoglycerate mutase; PGK-phosphoglycerate kinase; PPL-myophosphorylase; RRF-ragged red fibers; TFP-trifunctional protein deficiency; VLCAD-very long-chain acyl-coenzyme A dehydrogenase.

Assessment and management of fatigue in neuromuscular disease

Fatigue is a common and potentially debilitating symptom of neuromuscular disease (NMD). Studies show that patients with NMD subjectively report increased levels of fatigue. Laboratory testing has demonstrated that patients with NMD show objective physiological signs of increased fatigue, with both central and peripheral components. To date, no treatment has been proven to be truly effective through evidence-based medicine. Thus, the clinician must use a multimodality approach to treating fatigue in patients with NMD. Management interventions are generally based on a sequential approach including treatment of comorbid factors, with the goal of maximizing physical and psychological functioning. This might include low-intensity exercise training, cognitive therapy, treatment of associated depression, correction of risk factors such as obesity, poor nutrition, and inactivity (deconditioning). Optimizing cardiopulmonary function is also critical and measures such as noninvasive, positive pressure ventilation may reduce fatigue in patients with NMD. Novel medications such as modafinil, a nonamphetamine stimulant, may be a helpful pharmacological treatment. Nutraceutical agents, such as creatine monohydrate, coenzyme Q10 (CoQ10), and alpha-lipoic acid, may also improve neuromuscular function and reduce fatigue.

A second MNGIE patient without typical mitochondrial skeletal muscle involvement

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease caused by mutations in the gene encoding thymidine phosphorylase (TYMP). Clinically, MNGIE is characterized by gastrointestinal dysmotility, cachexia, ptosis, ophthalmoparesis, peripheral neuropathy and leukoencephalopathy. Most MNGIE patients have signs of mitochondrial dysfunction in skeletal muscle at morphological and enzyme level, as well as mitochondrial DNA depletion, multiple deletions and point mutations. A case without mitochondrial skeletal muscle involvement and with a TYMP splice-acceptor site mutation (c. 215-1 G>C) has been reported. Here, we describe an Italian patient with the same mutation and without mitochondrial skeletal muscle involvement, suggesting a possible genotype-phenotype correlation.

The evolution of mass spectrometry in the clinical laboratory

Clinical laboratories around the world are recognizing the power of mass spectrometry. This technique, especially when coupled to gas chromatography or liquid chromatography, is revolutionizing the analysis of many analytes. Unlike many other techniques which measure one analyte at a time, these techniques can measure multiple analytes (>40) at one time. In recent years the scope of testing using these techniques has expanded from toxicological purposes to newborn screening to hormones, proteins, and enzymes. It is not uncommon any more to see mass spectrometry being used in the routine clinical laboratories.

Lipid oxidation and peroxidation in CNS health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) are produced at low levels in mammalian cells by various metabolic processes, such as oxidative phosphorylation by the mitochondrial respiratory chain, NAD(P)H oxidases, and arachidonic acid oxidative metabolism. To maintain physiological redox balance, cells have endogenous antioxidant defenses regulated at the transcriptional level by Nrf2/ARE. Oxidative stress results when ROS production exceeds the cell's ability to detoxify ROS. Overproduction of ROS damages cellular components, including lipids, leading to decline in physiological function and cell death. Reaction of ROS with lipids produces oxidized phospholipids, which give rise to 4-hydroxynonenal, 4-oxo-2-nonenal, and acrolein. The brain is susceptible to oxidative damage due to its high lipid content and oxygen consumption. Neurodegenerative diseases (AD, ALS, bipolar disorder, epilepsy, Friedreich's ataxia, HD, MS, NBIA, NPC, PD, peroxisomal disorders, schizophrenia, Wallerian degeneration, Zellweger syndrome) and CNS traumas (stroke, TBI, SCI) are problems of vast clinical importance. Free iron can react with H(2)O(2) via the Fenton reaction, a primary cause of lipid peroxidation, and may be of particular importance for these CNS injuries and disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Atherosclerosis, the major risk factor for ischemic stroke, involves accumulation of oxidized LDL in the arteries, leading to foam cell formation and plaque development. This review will discuss the role of lipid oxidation/peroxidation in various CNS injuries/disorders.

Imitators of exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) is described by transient narrowing of the airways after exercise. It occurs in approximately 10% of the general population, while athletes may show a higher prevalence, especially in cold weather and ice rink athletes. Diagnosis of EIB is often made on the basis of self-reported symptoms without objective lung function tests, however, the presence of EIB can not be accurately determined on the basis of symptoms and may be under-, over-, or misdiagnosed. The goal of this review is to describe other clinical entities that mimic asthma or EIB symptoms and can be confused with EIB.

[McArdle disease revealed by exercise intolerance associated with severe rhabdomyolysis]

McArdle's disease (MAD) is a rare hereditary myopathy secondary to a deficit in myophosphorylase, an essential enzyme for the use of muscular glycogen reserves. Exercise intolerance to a variable degree is the fundamental manifestation. Muscular enzymes are usually normal or slightly elevated, except during episodes of rhabdomyolysis. Generally, the electromyogram has poor sensitivity for the diagnosis of exercise myopathies. The muscular biopsy can be misleadingly normal. The role of MRI in the diagnosis of MAD is not well clarified in the literature. We report the case of a 16-year-old patient, hospitalized in July 2008 for exercise intolerance. On admission, he was asymptomatic and the physical examination was non contributive. Serum creatine kinase levels and renal function measures were normal. Cycloergometer exercise testing unmasked the disease. EMG and muscular biopsies were normal. During the second hospitalization, this time for rhabdomyolysis, T2 weighted MRI of the thighs showed high intensity signals from the gracilis muscles. The control MRI, made after 2 weeks of rest, was normal. Right gracilis muscle biopsy demonstrated excess glycogen with myophosphorylase deficiency, establishing the diagnosis of MAD. MAD is a rare metabolic myopathy to consider in patients with a history of exercise intolerance. The muscle biopsy can be misleadingly normal and should be, to our opinion, be guided by MRI findings.