Myopathies

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A myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. These conditions have widely varying etiologies, including congenital or inherited, idiopathic, infectious, metabolic, inflammatory, endocrine, and drug-induced or toxic.

Important information to obtain during the patient’s history includes the following:

The common symptoms of myopathy are muscle weakness, impaired function in activities of daily life, and, rarely, muscle pain and tenderness. Significant muscle pain and tenderness without weakness should prompt consideration of other causes.

General signs and symptoms of myopathy include the following:

The acuity of symptom onset may aid in the diagnosis, as follows:

Indications of which muscle groups are involved include the following symptoms:

See Clinical Presentation for more detail.

Laboratory testing

The following laboratory tests may be used to evaluate patients with myopathies:

Other studies may include the following:

See Workup for more detail.

The treatment of a myopathy is dependent on its etiology and can range from supportive and symptomatic management to therapy for specific conditions. Such treatments may include the following:

See Treatment for more detail.

Myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. Etiologies vary widely. The common symptoms are muscle weakness, impaired function in activities of daily life, and, rarely, muscle pain and tenderness. Presence of discolored or dark urine suggests myoglobinuria.

For the emergency physician, it is important to distinguish neurologic from muscular dysfunction. However, in the face of profound weakness, establishing ABCs (airway, breathing, circulation) with attention to airway and aspiration precautions and providing supportive care are indicated while inpatient consultation and detailed studies are performed.

Most congenital myopathies or inherited myopathies are chronic slowly progressive diseases. The emergency physician rarely attends to a patient specifically to treat congenital myopathy unless acute deterioration occurs. Emergency physicians attend to patients with metabolic, [1] inflammatory, endocrine, and toxic causes of myopathy more often than those with congenital causes because of the acute or subacute onset of symptoms associated with noncongenital forms. [2]

Periodic paralyses are a group of diseases that cause patients to present with acute weakness due to potassium shifts, leading to muscle dysfunction. A genetic defect of the sodium ion channel in muscle cell membranes is responsible for the paralysis, which may last from hours to days.

Idiopathic myopathies are thought to result from immune-mediated phenomena including sarcoidosis with myopathy, polymyositis, and dermatomyositis. Some idiopathic myopathies are associated with connective tissue disease, eg, systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and polyarteritis nodosa.

Acute alcoholic myopathy should be considered in patients who, after binging on alcohol, present with muscle pain that mostly involves limb weakness and myoglobinuria. Note the following:

Infectious causes include the following:

Endocrine causes of myopathy include the following:

Drug-induced or toxic causes of myopathy include use of the following [4] :

Acute periodic paralysis may be classified as hypokalemic, hyperkalemic, or normokalemic. Note the following:

Thyrotoxic periodic paralysis and Conn syndrome (ie, primary hyperaldosteronism) occur in Asians and are considered to have low potassium as the mechanism for paralysis. Treatment of the underlying disease and electrolyte disorder are curative.

Excessive licorice ingestion, as well as a myriad of other causes of hypokalemia, can cause paralysis.

Muscular dystrophies are chronic, progressive, inherited myopathies that present from early childhood to adolescence, as follows:

The prognosis varies depending on the etiology. The morbidity and mortality of myopathies is related to the etiology of the condition, severity of disease, and the presence of comorbid conditions. Severe weakness may lead to respiratory failure and death.

Thyrotoxic hypokalemic periodic paralysis is known to occur in Asian men, and one study suggests that Polynesians are also at risk for this condition. [7]

Angelini C. Spectrum of metabolic myopathies. Biochim Biophys Acta. 2015 Apr. 1852(4):615-21. [Medline].

Nance JR, Dowling JJ, Gibbs EM, Bonnemann CG. Congenital myopathies: an update. Curr Neurol Neurosci Rep. 2012 Apr. 12(2):165-74. [Medline].

Plate AM, Boyle BA. Musculoskeletal manifestations of HIV infection. AIDS Read. 2003 Feb. 13(2):62, 69-70, 72, 76. [Medline].

Valiyil R, Christopher-Stine L. Drug-related myopathies of which the clinician should be aware. Curr Rheumatol Rep. 2010 Jun. 12(3):213-20. [Medline]. [Full Text].

Mangravite LM, Engelhardt BE, Medina MW, et al. A statin-dependent QTL for GATM expression is associated with statin-induced myopathy. Nature. 2013 Oct 17. 502(7471):377-80. [Medline].

Muntean DM, Thompson PD, Catapano AL, et al. Statin-associated myopathy and the quest for biomarkers: can we effectively predict statin-associated muscle symptoms?. Drug Discov Today. 2017 Jan. 22(1):85-96. [Medline].

Elston MS, Orr-Walker BJ, Dissanayake AM, Conaglen JV. Thyrotoxic, hypokalaemic periodic paralysis: Polynesians, an ethnic group at risk. Intern Med J. 2007 May. 37(5):303-7. [Medline].

Wortmann RL. Lipid-lowering agents and myopathy. Curr Opin Rheumatol. 2002 Nov. 14(6):643-7. [Medline].

Kuncl RW. Agents and mechanisms of toxic myopathy. Curr Opin Neurol. 2009 Oct. 22(5):506-15. [Medline].

Carstens PO, Schmidt J. Diagnosis, pathogenesis and treatment of myositis: recent advances. Clin Exp Immunol. 2014 Mar. 175(3):349-58. [Medline].

Tansley SL, McHugh NJ. Serological subsets of juvenile idiopathic inflammatory myopathies–an update. Expert Rev Clin Immunol. 2016. 12(4):427-37. [Medline].

Babu S, Li Y. Statin induced necrotizing autoimmune myopathy. J Neurol Sci. 2015 Apr 15. 351(1-2):13-7. [Medline].

Cherin P, Belizna C, Cartry O, et al. Long-term subcutaneous immunoglobulin use in inflammatory myopathies: A retrospective review of 19 cases. Autoimmun Rev. 2016 Mar. 15(3):281-6. [Medline].

Mathevon L, Michel F, Decavel P, Fernandez B, Parratte B, Calmels P. Muscle structure and stiffness assessment after botulinum toxin type A injection. A systematic review. Ann Phys Rehabil Med. 2015 Dec. 58(6):343-50. [Medline].

Allen DG, Whitehead NP, Froehner SC. Absence of dystrophin disrupts skeletal muscle signaling: roles of Ca2+, reactive oxygen species, and nitric oxide in the development of muscular dystrophy. Physiol Rev. 2016 Jan. 96(1):253-305. [Medline].

Fischer S, Julius U. Management of patients with statin intolerance. Atheroscler Suppl. 2017 Nov. 30:33-7. [Medline].

Statland JM, Fontaine B, Hanna MG, et al. Review of the diagnosis and treatment of periodic paralysis. Muscle Nerve. 2017 Nov 10. [Medline].

Lee TW, Bae E, Hwang K, et al. Severe hypokalemic paralysis and rhabdomyolysis occurring after binge eating in a young bodybuilder: Case report. Medicine (Baltimore). 2017 Oct. 96(40):e8251. [Medline].

Patel K, McCoy JV, Davis PM. Recognizing thyrotoxic hypokalemic periodic paralysis. JAAPA. 2018 Jan. 31(1):31-4. [Medline].

Courtney A Bethel, MD, MPH Clinical Assistant Professor, Department of Emergency Medicine, Mercy Catholic Medical Center, Drexel University School of Medicine

Courtney A Bethel, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Paul Blackburn, DO, FACOEP, FACEP Attending Physician, Department of Emergency Medicine, Maricopa Medical Center

Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, Arizona Medical Association, American College of Osteopathic Emergency Physicians, American Medical Association

Disclosure: Nothing to disclose.

Barry E Brenner, MD, PhD, FACEP Professor of Emergency Medicine, Professor of Internal Medicine, Program Director for Emergency Medicine, Sanz Laniado Medical Center, Netanya, Israel

Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, New York Academy of Medicine, New York Academy of Sciences, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Jerry R Balentine, DO, FACEP, FACOEP Vice President, Medical Affairs and Global Health, New York Institute of Technology; Professor of Emergency Medicine, New York Institute of Technology College of Osteopathic Medicine

Jerry R Balentine, DO, FACEP, FACOEP is a member of the following medical societies: American College of Emergency Physicians, New York Academy of Medicine, American College of Osteopathic Emergency Physicians, American Association for Physician Leadership, American Osteopathic Association

Disclosure: Nothing to disclose.

Myopathies

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