Hertz Muscles Flashcards
Type I vs Type II muscles
One slow fat red ox
I: sustained force, aerobic exercise, low power, high resistance to fatigue, high lipid content, low glycogen content, low glycolytic capacity, high oxidative capacity, high mitochondrial density
Type II: fast movement, anaerobic exercise, high power, low resistance to fatigue, low lipid content, high glycogen content,
muscle biopsy pattern should look like
checkerboard- even spread of light and dark
Skeletal Muscle Atrophy
Clusters or groups of atrophic fibers are seen in neurogenic disease
** Perifascicular atrophy is seen in dermatomyositis
Type II fiber atrophy with sparing of type I fibers is seen with prolonged corticosteroid therapy or disuse atrophy
Neurogenic and Myopathic Changes in Skeletal Muscle
Disorders impacting skeletal muscle may do so by damaging myofibers directly (myopathic injury) or by disrupting muscle innervation (neurogenic injury). Neurogenic injuries lead to ** fiber type grouping and grouped atrophy**
Other changes: can see Segmental myofiber degeneration and regeneration, myofiber hypertrophy, or cytoplasmic inclusions
Segmental myofiber degeneration and regeneration
is seen when only part of a myofiber undergoes necrosis. Degeneration is associated with release of cytoplasmic enzymes into the blood such as * creatine kinase, making these useful markers of muscle damage.
Myofiber hypertrophy
physiologic adaptation to exercise or in association with certain chronic myopathic conditions.
Cytoplasmic inclusions (muscle)
in the form of vacuoles, aggregates of proteins, or clustered organelles are characteristic of several primary forms of myopathy.
Inflammatory Myopathies
Historically, * polymyositis, * dermatomyositis, and * inclusion body myositis have been considered the three main primary inflammatory myopathies; however, inclusion body myositis is an enigmatic condition in which the role of inflammation is uncertain.
Other immune-mediated disorders, such as systemic lupus erythematosus, systemic sclerosis, and sarcoidosis, as well as certain infectious agents, can also cause myositis
proximal muscle weakness is what?
can’t get up out of a chair, e.g.
going up stairs wears out
Dermatomyositis
Dermatomyositis is a systemic autoimmune disease that typically presents with * proximal muscle weakness and skin changes
Dermatomyositis is an immunologic disease in which damage to small blood vessels contributes to muscle injury
mechanic’s hands
anti Jo-1
Autoantibodies in dermatomyositis
Anti-Mi2 antibodies (directed against a helicase implicated in nucleosome remodeling) show a strong association with prominent * Gottron papules and heliotrope rash.*
Anti-Jo1 antibodies (directed against the enzyme histidyl t-RNA synthetase) are associated with interstitial lung disease, nonerosive arthritis, and a skin rash described as “mechanic’s hands.”
Anti-P155/P140 antibodies (directed against several transcriptional regulators) are associated with paraneoplastic and juvenile cases of dermatomyositis.
CREST syndrome
Calcinosis Reynaud's Esophageal dysmotility Sclerodactyly (sausage fingers) Telangiectasias
dermatomyositis clinical features
heliotrope rash, CREST syndrome, perifascicular rash, peripheral muscle weakness- elevation in serum creatine kinase
red patches over the knuckles, elbows, knees- Gottron papules
Dysphagia
interstitial lung disease
Polymyositis
adult-onset inflammatory myopathy that shares myalgia and weakness with dermatomyositis but lacks its distinctive cutaneous features
diffuse lymphocytes on mucle biopsy (spider web, not perifascicular)
CPK high
Inclusion Body Myositis
Inclusion body myositis is a disease of late adulthood that typically affects patients * older than 50 years and is the most common inflammatory myopathy in patients older than age 65 years
Most affected individuals present with slowly progressive muscle weakness that tends to be most severe in the * quadriceps and the distal upper extremity muscles
- do not get better with steroids
- stuff in the middle of the muscle cells
Treatment of Inflammatory Myopathies
Corticosteroids remain the first-line of treatment for polymyositis and dermatomyositis.
Immunosuppressive drugs are used in steroid-resistant disease or as steroid-sparing agents and include azathioprine and methotrexate. Intravenous immunoglobulin (IVIG), cyclophosphamide, cyclosporine, and rituximab (an antibody that targets B cells) are third-line therapies.
Inclusion body myositis usually responds poorly to steroids or immunosuppressive therapies, another feature that argues against an inflammatory or immune origin for this disorder.
Toxic Myopathies
Myopathy is the most common complication of statins
Chloroquine and hydroxychloroquine (antimalarial agents)
Thyrotoxic myopathy presents most commonly as an acute or chronic proximal muscle weakness that may precede other signs of hyperthyroidism
Alcohol can also be myopathic. Most notably, binge drinking may produce an acute toxic syndrome of rhabdomyolysis, myoglobinuria, and renal failure.
Muscular Dystrophies
include several inherited disorders of skeletal muscle that have in common progressive muscle damage that typically manifests itself between * childhood and adulthood
The most common muscular dystrophies are X-linked and stem from mutations that disrupt the function of a large structural protein called * dystrophin
- Duchenne and Becker muscular dystrophy are caused by loss-of-function mutations in the dystrophin gene on the X chromosome
Becker is like bud and bud light
later and less severe
Duchenne’s no dystrophin
Becker a little dystrophin
normal lots of dystrophin
clinical features of Duchenne muscular dystrophy
normal at birth. Very early motor milestones are met, but * walking is often delayed. The first indications of muscle weakness are clumsiness and inability to keep up with peers.
Weakness begins in the * pelvic girdle muscles and then extends to the shoulder girdle. Enlargement of the muscles of the lower leg associated with weakness, termed * pseudohypertrophy, is often present. The mean age of wheel chair dependence is around 9.5 years. Patients develop joint contractures, scoliosis, worsening respiratory reserve, and sleep hypoventilation.
- Serum creatine kinase is markedly elevated during the first decade of life due to ongoing muscle damage, and then falls as the disease progresses and muscle mass is lost. The presence of a dystrophin mutation can be confirmed by genetic studies
Gower’s sign
can’t get up normally
pushing on knees to get up
classic muscular dystrophy sign
mitochondrial myopathies- what do we see?
ragged red fibers at periphery of muscle fibers
young athlete
Spinal Muscular Atrophy and the Differential Diagnosis of a Hypotonic Infant
Spinal muscular atrophy is a neuropathic disorder in which loss of motor neurons leads to muscle weakness and atrophy
Infants with neurologic or neuromuscular disease may present with generalized hypotonia (“floppy infant”).
ddx of hypotonia: primary diseases of skeletal muscle (e.g., congenital myasthenic syndrome, congenital myotonia, congenital myopathies, and congenital muscular dystrophies), abnormalities of the brain (e.g. encephalopathy), and neuronopathies, of which spinal muscular atrophy is a prototypic example.
Ion Channel Myopathies (Channelopathies)
Symptomatic patients have elevated, depressed, or normal serum potassium levels and are called * hyperkalemic, hypokalemic, and normokalemic periodic paralysis*
linked to malignant hyperthermia
Upon exposure to anesthetic, the mutated receptor allows increased efflux of calcium from the sarcoplasmic reticulum, leading to tetany and excessive heat production.
DANTROLENE
