MUSCLE DISEASES Flashcards
2 pathologic processes that affect skeletal muscle
denervation atrophy (abnormality of the nerve)
mutation causing spinal muscular atrophy
survival motor neuron 1 - gene on chromosome 5
what is SMN1 required for
motor neuron survival
most common form of spinal muscular atrophy
werdnig - hoffman disease
spinal muscular atrophy inheritance
autosomal recessive
heterogenous group of inherited disorders that result in muscle weakness and eventually muscle atrophy and wasting with muscle being replaced by fibrofatty tissue
muscular dystrophy
cause of duchene muscular dystrophy and becker muscualr dystrophy
X linked gene that codes for dystrophin is mutated.
what does dystrophin do
tranfers contractile force to the connective tissue from the EC matrix
patients with this have little or no dystrophin
duchenne muscular dystrophy
when does DMD develop
by age 5
signs of DMD
Gowers maneuver
gowers maneuver
waddling duck like gait where they place hands on knees to assist standing
what’s increased in the disease
creatine kinase
mean survival with Duchene muscular dystrophy
35 years old
genetic tests used to establish diagnosis
peripheral blood
patients with this have DECREASED amounts of dystrophin or a DEFECTIVE or abnormal form of dystrophin
Becker muscular dystrophy
onset of Becker muscular dystrophy
later than Duchennes
survival with Becker muscular dystrophy
well into 40s and beyond
treatment for Becker muscular dystrophy
immunosupression
most common adult muscular dystrophy
myotonic dystrophy
myotonia
sustained involuntary contraction of group of muscles
inheritance of myotonic dystrophy
autosomal dominant
type of disorder that myotonic dystrophy is and the chromosome it affects
trinucleotide repeat disorder on chromosome 19
what does myotonic dystrophy affect
mRNA for dystrophia myotonia protein kinase that results in defects affecting transcription of proteins for chloride channel
patient presentation with myotonic dystrophy
abnormal gait
what do tests for myotonic dystrophy show
elevated creatine kinase
group of diseases caused by mutations affecting function of ion channel proteins
ion channel myopathies
clinical manifestation of ion channel myopathies
epilepsy
what can ion channel myopathies affect
potassium
what do ion channel myopathies result in
hypotonia (decreased muscle tone) or hypertonia (increased muscle tone)
what are the clinical symptoms of malignant hyperpyrexia (malignant hyperthermia)
hyperbolic state - tachycardia, tachypnea, muscle spasms
what triggers malignant hyperthermia
anesthetics
what mutation leads to malignant hyperthermia
mutations that encode proteins that control levels of cytosolic calcium. Channels release calcium concontrollably.
Is malignant hyperthermia a medical emergency
Yes. there is excessive heat production and increased muscle metabolism.
often manifest in infancy and may include inborn errors of metabolism
congenital myopathies
3 types of inflammatory myopathies
Infectious
infectious inflammatory myopathies
necrotizing fasciitis, clostridial gangrene, etc.
systemic disease inflammatory myopathies
systemic lupus
Noninfectious inflammatory diseases (3)
dermatomyositis
autoimmune disease w/immunologic injury and damage to small blood vessels and capillaries in skeletal muscle, along with skin involvment and characteristic rash
dermatomyositis
main signs of dermatomyositis
muscle weakness
presentation of rash
discoloration of upper eyelids, scaling red rash, dusty patches over knuckles, knees, and elbows
presentation of muscle weakness
affects PROXIMAL MUSCLES first and is often SYMMETRIC
what can be found with dermatomyositis
15-25% of patients have underlying malignancy
what do patients have elevated
creatine kinase
has muscle and systemic involvement but NO skin involvement
polymyositis
where is polymyositism mainly seen (what age)
adults
what are autoantibodies directed against in polymyositis
histidyl t-RNA synthetase
what is though to cause polymyositis
activated CD8+ T cells
what is elevated with polymyositis
creatine kinase
treatment for polymyositis and dermatomyositis
immunosupressive agents
typically affects people older than 50 and involves DISTAL MUSCLES FIRST
inclusion body myositis
muscle pattern involvement with inclusion body myositis
asymmetric
shows MODEST elevations of creatine kinase
inclusion body myositis
does inclusion body myositis show benefit with immunosuppressive agents
No
3 toxic myopathies
Thyrotoxic myopathy
disease characterized by loss of function of the acetylcholine receptor
myasthenia gravis
what can you detect with myasthenia gravis
autoantibodies that lead to degradation of the receptor
what can some people have antibodies directed against?
tyrosine kinase - interferes with the function of the receptor
what is myasthenia gravis often associated with
thymic abnormalities
treatment for myasthenia gravis
anticholinesterase drugs
presents with extremity weakness
lambert-eaton myastenia syndrome
what does lambert-eaton myastenia syndrome have autoantibodies directed against
presynaptic calcium channels - block acetylcholine release
what can increase muscle response with lambert-eaton myastenia syndrome
rapid repetitive stimulation of the muscle
what is lambert-eaton myastenia syndrome often seen with
paraneoplastic syndrome w/malignancy present in 60% (often small cell lung carcinoma)
do patients show improvement w/anticholinesterase agents
No
enzyme that converts creatine to phosphocreatine
creatine kinase
creatine kinase that skeletal muscle expresses
CK-MM
creatine kinase that gets expressed as skeletal muscle is damaged
CK-MB
creatine kinase expressed at low levels in many tissues
CK-BB
where is creatine kinase released when cells are damaged
interstitial space and blood
conditions with elevated creatine kinase
acute myocardial infart
used for diagnosing acute myocardial infart
cardiac troponin I
when is total creatine kinase helpful in assessment of skeletal muscle injury
when there is absence of cardiac disease or other conditions that may cause increased CK
where is myoglobin found
skeletal and cardiac muscle
disease where elevated levels of myoglobin can cause acute tubular necrosis with acute renal failure
rhabdomyolysis