In
medicine, myopathy is a
disease of the
muscle[1] 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 (initially normal, but declining muscle force).
Muscle cramps,
stiffness,
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 (abnormally large).
Capture myopathy can occur in wild or captive animals, such as deer and
kangaroos, and leads to morbidity and mortality.[2] 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. Some conditions, such as
myositis, can be considered both neuromuscular and musculoskeletal. 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.[citation needed]
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 related,[3] and myopathies with other systemic disorders. Patients with systemic myopathies often present
acutely or sub acutely. 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.[4] 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.[5]
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, often leading to use of a
wheelchair, and eventually death, usually related to
respiratory weakness.
(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 disorder
(G72.4)
Inflammatory myopathies, which are caused by problems with the immune system attacking components of the muscle, leading to signs of
inflammation in the muscle
(G73.6)
Metabolic myopathies, which result from defects in biochemical metabolism that primarily affect muscle
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.
The Food and Drug Administration is recommending that physicians restrict prescribing high-dose
Simvastatin (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.
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, bracing for support,
surgery, and massage are all current treatments for a variety of myopathies.[citation needed]
^Green-Barber JM, Stannard HJ, Old JM (2018). "A suspected case of myopathy in a free-ranging eastern grey kangaroo (Macropus giganteus)". Australian Mammalogy. 40: 122–126.
doi:
10.1071/AM16054.
^Voermans NC, van Alfen N, Pillen S, Lammens M, Schalkwijk J, Zwarts MJ, van Rooij IA, Hamel BC, van Engelen BG (June 2009). "Neuromuscular involvement in various types of Ehlers-Danlos syndrome". Ann. Neurol. 65 (6): 687–97.
doi:
10.1002/ana.21643.
PMID19557868.
S2CID22600065.