Musculoskeltal System: Lec.7 - Diseases Of Skeletal Muscle

Front 1

Musculoskeltal System Lecture 7 Diseases of Skeletal Muscle

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Musculoskeltal System Lecture 7 Diseases of Skeletal Muscle

Front 2

7Q:

most common form of denervation atrophy is....

Back 2

Werdnig-Hoffmann Disease, SMA Type 1

-atrophy caused by any process that affects the anterior horn cell or it’s processes in the peripheral nervous system

Spinal Muscular Atrophy (SMA)- autosomal recessive motor neuron diseases
-locus on chromosome 5

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7Q:

most common muscular dystrophy, and a brief description

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Duchenne MD:
-x-linked MD
-more boys than girls. (1:3500)
normal at birth but by age 5 get weakness, and by 12 need a wheelchair
-heart and cognitive impairment components

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7Q:

Histological findings to X-linked MDs

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-Variation in fiber size
-Increased numbers of internalized nuclei
-Degeneration of muscle fibers
-Regeneration of muscle fibers
-Proliferation of enomysial connective tissue

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7Q:

What gene is related to x-linked MDs, and what does it encode?

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Xp21 region and encodes a 427-kD protein

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7Q:

Whats the difference between Duchenne and Beckers?

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same genetic locus as Duchenne muscular dystrophy but is less common and much less severe, onset occurs later in childhood or in adolescence and has a slower, more variable rate of progression

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7Q:

Where does Limb Girdle Muscular Dystrophies Affect?

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LGMDs affect the proximal musculature of the trunk and limbs with either an autosomal (LGMD1) or recessive (LGMD2) inheritance.

Dystrophin interaction with mutated proteins in recessive LGMDs.

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7Q:

How does Myotonic Dystrophy present

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abnormalities in gait, secondary weakness of foot dorsiflexor, weakness with atrophy of muscles of the face, and pstosis

-autosomal dominant that increases with severity
-sustained, involuntary contraction of a group of muscles!!!
-gene contains a trinucleotide repeat- the disease is caused by repeat expansion.

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7Q:

How is myotonic dystrophy different from other dystrophies?

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Myotonic dystrophy is the only dystrophy that shows pathologic changes in muscles spindles, with fiber splitting, necrosis, and regeneration

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7Q:

Whats the deal with Malignant hyperpyrexia (malignant hyperthermia) ?

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it's an autosomal dominant, ion channel myopathy. there's dramatic hypermetabolism (tachycardia, tachypnea, muscle spasms, hyperpyrexia)
-triggered by induction of ANESTHESIA, halogenated inhaled agents, succinylcholine.

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7Q:

name an example of a congenital myopathy

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floppy babies from hypotonia. congenital myopathies are characterized by onset early in life, non or slowly progressive course, proximal or generalized muscle weakness, severe joint contractures

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7Q:

Whats a common issue with myopathies associated with inborn errors of metabolism?

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association with glycogen synthesis and degradation, and can also result from disorders of mitochondrial function

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7Q:

whats the main morphologic characteristic of lipid myopathies?

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it's accumulation of lipid withint the myoctyes in vacuoles. these myopathies are caused by carnitine transport system abnormalities/deficiencies of mitochondrial dehydrogenase enzyme systems

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7Q:

Whats the important point with myopathies with metabolic issues?

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you have myoglobin in the urine, and the next thing you know, you have renal failure.

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7Q:

What can binge drinking cause?

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acute toxic syndrome of rhabdomyolysis with accompanying myoglobinuria, which can lead to renal failure.

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7Q:

What in the world is Thyrotoxic Myopathy?

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acute or chronic, proximal muscle weakness sometimes presents before clinical thyroid dysfunction. In thyrotoxic periodic paralysis, there is weakness and hypokalemia

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7Q:

What determines a steroid toxic myopathy?

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not dependent on the amount of steroids used, but instead it's the patient sensitivity.

myopathies may occur in Cushing syndrome or therapeutic admin. of steroids.

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7Q:

Distinguish the three types of Inflammatory Myopathies.

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Infectious- directly involved with muscle; invasion from skin into the muscle.

Noninfectious- associated rash with the muscle issues. including polymyositis, dermatomyositis, and inclusion body myositis

Systemic- muscles and other organs

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7Q:

Big example of a neuromuscular junction disorder is...

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Myasthenia gravis-

an autoimmune disease characterized clinically be easy fatigability, ptosis, and diplopia resulting from an immune-mediated injury, which causes a decree in the number of muscle acetylcholine receptors (AChRs)

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7Q:

What is present in about 90% of Myasthenia Gravis patients?

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antibodies to AChR is found in the serum. These antibodies accelerate degradation of the AChR.

Tx with plasmapheresis
Ladies got it more.

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7Q:

What is found in up to 75% of the patients with myasthenia gravis?

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Thymic hyperplasia is seen in about 65 to 75% of patients, and a thymoma is found in 15%. Resection of thymoma can improve symptoms

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7Q:

Whats the difference between Lambert-Eaton Myasthenic Syndrome and Myasthenia Gravis?

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It has increased contractions with repeated stimuli.

it is a paraneoplastic NM junction disorder, mostly with small cell carcinoma of the lung (60%).

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7Q:

Four types of Rhabdomyosarcomas
(tumors of skeletal muscle):

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1.Embryonal
2.Botryoid- project into cavity (vagina, bladder, as grapelike masses)
3.Alveolar
4. Pleomoprhic- rare, in old pts. large tumor cells with a lot of cytoplasm, cross-striations

*all but pleomorphic responds to surgery/radiation/chemotherapy.

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7Q:

What is Leiomyoma and leiomyosarcoma

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Benign smooth muscle tumors occur predominantly in the female genital tract

leiomyomas are more common.
mostly developed in skin and deep soft tissue.

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7Q:

How do Leiomyoma and leiomyosarcoma present? tx?

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They are usually large, soft, gray masses of spindle cells with cigar-shaped nuclei
Variants may be myxoid or epithelioid

Superficial lesions often can be excised; deep tumors are invasive and rarely excisable