In
medicine
Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...
, myopathy is a
disease
A disease is a particular abnormal condition that adversely affects the structure or function (biology), function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical condi ...
of the
muscle
Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
in which the
muscle fibers do not function properly. ''Myopathy'' means muscle disease (
Greek : myo- ''muscle'' + patheia ''
-pathy'' : ''suffering''). This meaning implies that the primary defect is within the muscle, as opposed to the nerves ("
neuropathies" or "
neurogenic" disorders) or elsewhere (e.g., the brain).
This muscular defect typically results in
myalgia (muscle pain),
muscle weakness (reduced muscle force), or premature
muscle fatigue
Muscle fatigue is when muscles that were initially generating a normal amount of force, then experience a declining ability to generate force. It can be a result of vigorous exercise, but abnormal fatigue may be caused by barriers to or interfer ...
(initially normal, but declining muscle force).
Muscle cramps,
stiffness
Stiffness is the extent to which an object resists deformation in response to an applied force.
The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.
Calculations
The stiffness, k, of a ...
,
spasm, and
contracture can also be associated with myopathy. Myopathy experienced over a long period (chronic) may result in the muscle becoming an abnormal size, such as
muscle atrophy (abnormally small) or a
pseudoathletic appearance
Pseudoathletic appearance is a medical sign meaning to have the false appearance of a well-trained athlete due to pathologic causes (disease or injury) instead of true athleticism. It is also referred to as a Herculean or bodybuilder-like ap ...
(abnormally large).
Capture myopathy can occur in wild or captive animals, such as deer and
kangaroos, and leads to morbidity and mortality. It usually occurs as a result of stress and physical exertion during capture and restraint.
Muscular disease can be classified as
neuromuscular or
musculoskeletal in nature. Different myopathies may be inherited, infectious, non-communicable, or idiopathic (cause unknown). The disease may be isolated to affecting only muscle (pure myopathy), or may be part of a systemic disease as is typical in
mitochondrial myopathies.
Signs and symptoms
Common symptoms include muscle weakness, cramps, stiffness, and
tetany.
Systemic diseases
Myopathies in systemic disease results from several different disease processes including
endocrine,
inflammatory,
paraneoplastic, infectious, drug- and toxin-induced, critical illness myopathy, metabolic,
collagen
Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...
related,
and myopathies with other systemic disorders. Patients with systemic myopathies often present
acutely or subacutely. On the other hand,
familial myopathies or
dystrophies generally present in a
chronic fashion with exceptions of
metabolic myopathies, where symptoms on occasion can be precipitated acutely. Metabolic myopathies, which affect the production of ATP within the muscle cell, typically present with
dynamic (exercise-induced) rather than static symptoms. Most of the
inflammatory myopathies can have a chance association with malignant lesion; the incidence appears to be specifically increased only in patients with dermatomyositis.
There are many types of myopathy.
ICD-10 codes are provided here where available.
Inherited forms
* (G71.0)
Dystrophies (or muscular dystrophies) are a subgroup of myopathies characterized by muscle degeneration and regeneration. Clinically, muscular dystrophies are typically progressive, because the muscles' ability to regenerate is eventually lost, leading to progressive weakness and often leading to use of a
wheelchair
A wheelchair is a mobilized form of chair using two or more wheels, a footrest, and an armrest usually cushioned. It is used when walking is difficult or impossible to do due to illnesses, injury, disabilities, or age-related health conditio ...
and eventually death, usually related to
respiratory weakness.
* (G71.1)
Myotonia
**
Neuromyotonia
* (G71.2) The
congenital myopathies do not show evidence for either a progressive dystrophic process (i.e., muscle death) or inflammation, but instead characteristic microscopic changes are seen in association with reduced contractile ability of the muscles. Congenital myopathies include, but are not limited to:
** (G71.2)
nemaline myopathy (characterized by presence of "nemaline rods" in the muscle),
** (G71.2)
multi/minicore myopathy (characterized by multiple small "cores" or areas of disruption in the muscle fibers),
** (G71.2)
centronuclear myopathy (or myotubular myopathy) (in which the
nuclei are abnormally found in the center of the muscle fibers), a rare muscle
wasting
In medicine, wasting, also known as wasting syndrome, refers to the process by which a debilitating disease causes muscle and fat tissue to "waste" away. Wasting is sometimes referred to as "acute malnutrition" because it is believed that epis ...
disorder.
* (G71.3)
Mitochondrial myopathies, which are due to defects in
mitochondria, which provide a critical source of energy for muscle
* (G72.3) Familial
periodic paralysis
* (G72.4)
Inflammatory myopathies, which are caused by problems with the immune system attacking components of the muscle, leading to signs of
inflammation
Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...
in the muscle
* (G73.6)
Metabolic myopathies, which result from defects in biochemical metabolism that primarily affect muscle
** (G73.6/E74.0)
Glycogen storage disease
A glycogen storage disease (GSD, also glycogenosis and dextrinosis) is a metabolic disorder caused by a deficiency of an enzyme or transport protein affecting glycogen synthesis, glycogen breakdown, or glycolysis, glucose breakdown, typically in m ...
s, which may affect muscle
** (G73.6/E75)
Lipid storage disorder
* (G72.89) Other myopathies
**
Brody myopathy
**
Congenital myopathy with abnormal subcellular organelles
**
Fingerprint body myopathy
**
Inclusion body myopathy 2
**
Megaconial myopathy
**
Myofibrillar myopathy
**
Rimmed vacuolar myopathy
Acquired
* (G72.0 - G72.2) External substance induced myopathy
** (G72.0) Drug-induced myopathy
***
Glucocorticoid
Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebra ...
myopathy is caused by this class of steroids
increasing the breakdown of the muscle proteins leading to
muscle atrophy.
** (G72.1)
Alcoholic myopathy
** (G72.2) Myopathy due to other toxic agents, including
atypical myopathy in
horses caused by toxins in
sycamore seeds and seedlings.
* (M33.0-M33.1)
**
Dermatomyositis produces muscle weakness and skin changes. The skin rash is reddish and most commonly occurs on the face, especially around the eyes, and over the knuckles and elbows. Ragged nail folds with visible capillaries can be present. It can often be treated by drugs like corticosteroids or immunosuppressants. (M33.2)
**
Polymyositis produces muscle weakness. It can often be treated by drugs like corticosteroids or immunosuppressants.
**
Inclusion body myositis is a slowly progressive disease that produces weakness of hand grip and straightening of the knees. No effective treatment is known.
* (M60.9)
Benign acute childhood myositis
* (M61)
Myositis ossificans
* (M62.89)
Rhabdomyolysis and (R82.1)
myoglobinurias
The Food and Drug Administration is recommending that physicians restrict prescribing high-dose
Simvastatin
Simvastatin, sold under the brand name Zocor among others, is a statin, a type of lipid-lowering medication. It is used along with exercise, diet, and weight loss to decrease hyperlipidemia, elevated lipid levels. It is also used to decrease t ...
(Zocor, Merck) to patients, given an increased risk of muscle damage. The FDA drug safety communication stated that physicians should limit using the 80-mg dose unless the patient has already been taking the drug for 12 months and there is no evidence of myopathy.
"Simvastatin 80 mg should not be started in new patients, including patients already taking lower doses of the drug," the agency states.
*
Statin-associated autoimmune myopathy
Myocardium / cardiomyopathy
* ()
Acute myocarditis
* ()
Myocarditis in diseases classified elsewhere
* ()
Cardiomyopathy
** ()
Dilated cardiomyopathy
** () Obstructive
hypertrophy cardiomyopathy
** () Other
hypertrophic cardiomyopathy
** ()
Endomyocardial (
eosinophilic) disease
***
Eosinophilic myocarditis
***
Endomyocardial (tropical) fibrosis
***
Löffler's endocarditis
** ()
Endocardial fibroelastosis
** () Other
restrictive cardiomyopathy
** ()
Alcoholic cardiomyopathy
** () Other
cardiomyopathies
***
Arrhythmogenic right ventricular dysplasia
* ()
Cardiomyopathy in diseases classified elsewhere
Differential diagnosis
At birth''
* None as systemic causes; mainly hereditary
Onset in childhood
* Inflammatory myopathies: dermatomyositis, polymyositis (rarely)
* Infectious myopathies
* Endocrine and metabolic disorders: hypokalemia, hypocalcemia, hypercalcemia
Onset in adulthood
* Inflammatory myopathies: polymyositis, dermatomyositis, inclusion body myositis, viral (HIV)
* Infectious myopathies
* Endocrine myopathies: thyroid, parathyroid, adrenal, pituitary disorders
* Toxic myopathies: alcohol, corticosteroids, narcotics, colchicines, chloroquine
* Critical illness myopathy
* Metabolic myopathies
* Paraneoplastic myopathy
Treatments
Because different types of myopathies are caused by many different pathways, there is no single treatment for myopathy. Treatments range from treatment of the symptoms to very specific cause-targeting treatments.
Drug therapy,
physical therapy
Physical therapy (PT), also known as physiotherapy, is a healthcare profession, as well as the care provided by physical therapists who promote, maintain, or restore health through patient education, physical intervention, disease preventio ...
, bracing for support,
surgery
Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...
, and massage are all current treatments for a variety of myopathies.
References
External links
GeneReviews/NCBI/NIH/UW entry on Myopathy with Deficiency of ISCU* See http://neuromuscular.wustl.edu/ for medical descriptions.
{{Authority control
Muscular disorders