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Flashcards in Week 4 Muscle Diseases- Nelson Deck (7)
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Describe the genetic defect for spinal muscular atrophy.

a. Mutations affecting survival motor neuron 1 (SMN 1)
b. A gene on chromosome 5 that is required for motor neuron survival
c. Patients experience loss of motor neurons leading to muscle atrophy and weakness
d. Most common form = Werdnig-Hoffmann disease


Compare and contrast the pathogenesis and clinical outcome of Duchenne and Becker muscular dystrophy.

-Duchenne → have little or no dystrophin, symptoms by age 5, duck-like gate, wheel chair dependent by 10-12 years

Becker → decreased amounts of dystrophin or a defective abnormal form dystrophin, later onset with milder symptoms, longer survival


Describe the genetic defect for myotonic dystrophy

-Most common adult muscular dystrophy

-Increased CTG trinucleotide repeat sequences on chromosome 19 → effects chloride channel called CLC1


Describe the genetic defect and clinical presentation of malignant hyperpyrexia (malignant hyperthermia).

-Mutations in the proteins that control levels of cytosolic calcium

-Marked hypermetabolic state triggered by certain inhalational anestetics

-Tachycardia, tachypnea, muscle spasms, etc.


Compare and contrast the pathogenesis, clinical presentation, and pathologic findings of the 3 inflammatory myopathies.

-Dermatomyositis → immunologic injury and damage to small blood vessels and capillaries in the skeletal muscle (Skin + myositis). Discoloration of eyelids and Gottron papules → scaling erythematous eruption or dusky red patches over the knuckles, elbows, and knees. Clinical syndrome associated with malignancy!! Screen for malignancy!

-Polymyositis → similar but lacks skin involvement. Antibodies against histidyl t-RNA synthase caused by activated CD8+ cytotoxic T-cells.

-Inclusion Body Myositis → most common, begins with distal muscle involvement


Compare and contrast the pathogenesis and key clinical associations of myasthenia gravis and Lambert-Eaton myasthenia syndrome.

-Myastenia gravis → autoimmune disease causing loss of function of the acetylcholine receptor (AChR), sometimes antibody against muscle specific tyrosine kinase. Associated with thymic abnormalities

-Lamber-eaton myasthenia → autoantibodies against presynaptic calcium channels, which block actelycholine release. Extremity weakness, rapid repetivitive stimulation of affected muscle increases the muscle response. Paraneoplastic syndrome.


List the causes of elevated creatine kinase.

a. Myocardial infarct
b. Skeletal muscle disease such as inflammatory myopathies
c. Cerebrovascular accidents, head injury
d. *Total CK is helpful in the assessment of skeletal muscle inury in the absence of cardiac disease or other conditions that may cause increased CK.