Exam 5 muscular diseases Flashcards
Define muscular dystrophy
heterogenous group that results in muscle weakness and eventually muscle atrophy and wasting, muscle is replaced with fibrofatty tissue
T/F: most common muscular dystrophies are X-linked?
True; Duchenne’s MD, Becker MD
What is the gene that is deficient/mutated in muscular dystrophy? What does it do?
dystrophin; located adjacent to sarcolemma and forms interface between intracellular contractile units and extracellular connective tissue
What is the difference between Duchenne and Becker MD?
DMD have littler or no dystrophin, Becker have decreased amount of defective dystrophin
What are the two classical movement signs of DMD?
waddling “duck-like” gait, place hands on knees to assist standing (Gower’s maneuver)
What is pseudo hypertrophy? Where does it usually occur in DMD pts?
enlargement of calf due to replacement with adipose tissue
What is the blood marker of DMD pts?
elevated creatine kinase early in disease
What is the progression of DMD?
Develop symptoms by age 5, weakness in pelvic girdle, followed by shoulder girdle
What does a muscle biopsy of Becker’s MD and DMD show?
shows variation of muscle fiber size, increased endomysial connective tissue, degeneration of muscle fibers, replacement of muscle with fat and connective tissue
What is the treatment of BMD?
immunosuppression
What can female carriers of BMD be at risk for?
cardiomyopathy, will show increased creatine kinase
What is the genetic difference of myotonic dystrophy and DMD/BMD?
Myotonic is an autosomal dominant disorder, where as DMD/BMD are X-linked
What is incorrect in myotonic dystrophy?
increased CTG trinucleotide repeat sequences on chromosome 19, which affects mRNA for dystrophia myotonia protein kinase. Affects chloride channels
What do patients with myotonic dystrophy present with?
abnormal gait, weakness of hand and wrist, facial muscle atrophy/sagging face, ptosis (drooping eye) and open mouth
What does a muscle biopsy of myotonic dystrophy look like?
selective atrophy of type 1 fibers as well as ring fibers; elevated creatine kinase
What are the three subgroups of inflammatory myopathies?
Infection (group A strep, clostridial gas gangrene), Systemic inflammatory disease (SLE), Non-infectious inflammatory diseases (dermatomyositis)
What is dermatomyositis?
autoimmune against small blood vessels and capillaries in skeletal muscle; characteristic skin rash
What is the molecular/immunological basis of dermatomyositis?
activated B and T cells and antibodies with complement activation causing capillary damage
What are the classical clinical presentations of dermatomyositis?
Classic rash is violaceous discoloration of upper eyelids associated with periorbital edema, accompanied by scaling erythematous eruption or dusky red patches over joints (Gorton papule)
What are the lab values of dermatomyositis?
increased creatine kinase, treat w/ immunosuppressives
What does difference between polymyositis and dermatomyositis?
polymyositis has a lack of skin or vascular injury involvement
What is the pathogenesis of polymyositis?
caused by immunological injury to muscle by activated CD8+ T cells; muscle biopsy shows lymphatic inflammation surrounding and invading muscle fibers
What is the difference in terms of affects between dermatomyositis and polymyositis, and inclusion body myositis
Inclusion body myositis begins to affect distal muscles first
Do immunosuppressive agents help treat inclusion body myositis?
nope
What is the most common cause of drug-induced myopathies?
Statins
What is the cause of the symptoms of myasthenia gravis?
Antibodies against the nicotinic receptor at neuromuscular jxn
What are ways to diagnose myasthenia gravis?
detecting autoantibodies to nicotinic receptor, edrophonium test
What is the treatment of myasthenia gravis?
anti cholinesterase drugs (neostigmine, pyridostigmine, edrophonium)
What is the classical sign of Lambert-eaton myasthenia syndrome?
rapid repetitive stimulation of the affected muscle increases the muscle response; pts usually respond with extremity weakness
What causes Lambert-Eaton myasthenia syndrome?
autoantibodies against presynaptic calcium channels that blocks acetylcholine release
What are the three isotypes of creatine kinase?
CK-BB, CK-MB, CK-MM (B= brain, M= muscle)
What isoform is most dominant in skeletal muscle? What does it switch to when it’s damaged and is regenerating?
CK-MM; switches to CK-MB
What kinds of diseases is elevated creatine kinase seen in?
Skeletal muscle diseases such as inflammatory myopathies, muscular dystrophy, rhabdomyolysis, skeletal muscle trauma
What is the specific elevated blood protein seen after an MI?
cardiac troponin 1
What does myoglobinemia occur?
When cardiac or skeletal muscle is damaged
What can myoglobinuria cause?
rhabdomyolysis (acute tubular necrosis with acute renal failure)
