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Muscle Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Kourosh Rezania, Peter Pytel, Betty Soliven
Enzyme histochemical staining shows significantly reduced or absent myophosphorylase (Figure 27.20). Staining for phosphorylase could be falsely positive soon after an episode of rhabdomyolysis, probably because of upregulation of a fetal isoenzyme.
The locomotor system
Published in C. Simon Herrington, Muir's Textbook of Pathology, 2020
Muscle symptoms in these disorders are related to exercise intolerance. Defects in glycogen, lipid, purine nucleotide, and mitochondrial pathways can all lead to metabolic myopathies. McArdle's disease, the most common disorder of glycogen metabolism, is an inherited recessive disorder due to lack of myophosphorylase (Figure 13.48). Exercise intolerance with stiffness is found, symptoms usually being precipitated by brief bursts of high intensity activity. Severe attacks may involve rhabdomyolysis with myoglobinuria and hence renal failure.
Regulation of Sympathetic Nerve Activity in Humans: New Concepts Regarding Autonomic Adjustments to Exercise and Neurohumoral Excitation in Heart Failure
Published in Irving H. Zucker, Joseph P. Gilmore, Reflex Control of the Circulation, 2020
David W. Ferguson, Allyn L. Mark
In a subsequent study, SNA was recorded in patients with myophosphorylase deficiency (McArdle’s disease) who have impairment in glycolysis and so do not develop lactic acidosis during muscle contraction (Pryor et al., 1987). In these patients, sustained handgrip increased heart rate but did not decrease muscle pH and failed to increase muscle SNA despite cellular accumulation of Pi and ADP.
An update on diagnosis and therapy of metabolic myopathies
Published in Expert Review of Neurotherapeutics, 2018
Needle electromyography may be myopathic neuropathic, non-specifically abnormal, or normal in metabolic myopathies. A useful electrodiagnostic, provocative screening test for GSD-V is the long exercise test (LET) [24]. It relies on the recording of the compound muscle action potential (CMAP) before and after 5 min of isometric contraction [24]. In a study of 25 patients with GSD-V, the LET disclosed a post-exercise decrease of the CMAP amplitude in 23 of them [24]. The immediate and long-lasting decrease differentiated GSD-V patients from controls. Patients with a normal LET demonstrated milder symptoms or residual myophosphorylase activity [24]. The LET is a sensitive, safe, and non-invasive test that may guide clinicians toward molecular analysis of the PYGM gene [24]. The abnormalities observed on LET point toward complex biochemical mechanisms determined by the absence of myophosphorylase, beyond simple glycolytic blockade (ionic pump dysfunction, sarcolemmal inexcitability).
Pre- and peripartal management of a woman with McArdle disease: a case report
Published in Gynecological Endocrinology, 2018
Tina Stopp, Michael Feichtinger, Wolfgang Eppel, Thomas M. Stulnig, Peter Husslein, Christian Göbl
Glycogen storage disease type 5, also called McArdle disease, is an autosomal recessive inherited disorder in muscle metabolism caused by the lack or dysfunction of muscle glycogen phosphorylase (myophosphorylase). Due to this condition the ability to break down glycogen into glucose subunits within the skeletal muscle during muscle activity is inhibited. This results in intolerance to strenuous exercise which manifests as fatigue, muscle stiffness and myalgia, in some cases accompanied by myoglobinuria and in severe instances renal failure due to muscle breakdown and rhabdomyolysis [1]. Most Patients experience a period of less painful and more effective exercise after an initial period of muscle cramps. The so-called ‘second wind phenomenon’ is typical of McArdle disease [2]. This phenomenon is believed to be caused by a switch to alternative sources of energy such as fatty acid oxidation and an increased blood flow to the muscle [3]. The metabolic shift is more effective when the patient’s muscles are conditioned through regular aerobic exercise [4].
Multimodal imaging of posterior ocular involvement in McArdle's disease
Published in Clinical and Experimental Optometry, 2018
Giuseppe Casalino, Wing Chan, Clara Mcavoy, Michele Coppola, Francesco Bandello, Alan C Bird, Usha Chakravarthy
McArdle's disease is an extremely rare glycogen storage disease (type V), first reported by Brian McArdle in 1951.1951 This condition is characterised by rapid fatigue, myalgia and cramps in exercising muscles.2010 Manifestations of McArdle's disease are a direct result of deficiency of myophosphorylase function. Without this enzyme, the glycogenolysis pathway cannot adequately provide energy in the form of adenosine triphosphate for the maintenance of strenuous activity.2010 Homozygous or compound heterozygous mutations in the myophosphorylase gene, located on chromosome 11, are the cause of the deficiency of myophosphorylase function.2010