MUSCLE DISEASES Flashcards by Jill LaBine

2 pathologic processes that affect skeletal muscle

denervation atrophy (abnormality of the nerve)

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mutation causing spinal muscular atrophy

survival motor neuron 1 - gene on chromosome 5

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what is SMN1 required for

motor neuron survival

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most common form of spinal muscular atrophy

werdnig - hoffman disease

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spinal muscular atrophy inheritance

autosomal recessive

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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

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cause of duchene muscular dystrophy and becker muscualr dystrophy

X linked gene that codes for dystrophin is mutated.

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what does dystrophin do

tranfers contractile force to the connective tissue from the EC matrix

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patients with this have little or no dystrophin

duchenne muscular dystrophy

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when does DMD develop

by age 5

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signs of DMD

Gowers maneuver

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gowers maneuver

waddling duck like gait where they place hands on knees to assist standing

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what’s increased in the disease

creatine kinase

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mean survival with Duchene muscular dystrophy

35 years old

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genetic tests used to establish diagnosis

peripheral blood

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patients with this have DECREASED amounts of dystrophin or a DEFECTIVE or abnormal form of dystrophin

Becker muscular dystrophy

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onset of Becker muscular dystrophy

later than Duchennes

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survival with Becker muscular dystrophy

well into 40s and beyond

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treatment for Becker muscular dystrophy

immunosupression

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most common adult muscular dystrophy

myotonic dystrophy

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myotonia

sustained involuntary contraction of group of muscles

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inheritance of myotonic dystrophy

autosomal dominant

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type of disorder that myotonic dystrophy is and the chromosome it affects

trinucleotide repeat disorder on chromosome 19

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what does myotonic dystrophy affect

mRNA for dystrophia myotonia protein kinase that results in defects affecting transcription of proteins for chloride channel

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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

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

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