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Organ Pathology Exam 1 > Neuromuscular > Flashcards

Neuromuscular Flashcards

1
Q

What is the general structure of peripheral nerves and how do they interact with muscle fascicles?

A
  • conduct stimuli to and from spinal cord
  • Peripheral nerve fascicles interact with muscle fascicles at the neuromuscular junction
  • Degree of innervation corresponds to complexity of movements of innervated muscle group
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2
Q

Unmyelinated vs. myelinated nerves in the PNS

A

-Unmyelinated nerve fibers
Small diameter fibers (.2-.3 microns)
Intermingled with myelinated nerve fibers
Myelinated nerve fibers
-Schwann cells produce myelin sheaths with one cell providing all myelin within each internode
-Node of Ranvier: space between internodes
-Larger diameter fibers (2-15 microns)
-Thickness and length of internodes varies with axon size

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3
Q

What is a normal contractile unit composed of?

A
  • intermeshed actin and myosin fibrils
    Z band is junction between sarcomeres (dark band within pale I band)
    A band is central band
    I band is pale band that spans two sarcomeres (represents region of contraction-varies in size)
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4
Q

What’s the difference between type I and II skeletal muscle fibers? How are they staining-wise?

A

Type I mediate tonic contraction
-ATPase staining: dark at pH4.2 and light at pH9.4
Type II fibers mediate phasic contraction
-ATPase staining: light at pH4.2 and dark at pH9.4

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5
Q

What determines Type I vs. Type II?

A

Motor neuron that innervates muscle fiber determines type I vs. type II phenotype

Normally they are evenly intermixed in the fascicle

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6
Q

What are the classic features of neuromuscular disease?

A

Muscle weakness is hallmark:

  • Specific symptoms may suggest etiology
  • Poor dentition related to oro-facial weakness, impaired swallowing and general poor hygiene
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7
Q

What are the different etiologies of neuromuscular disease?

A
  • Peripheral nerve disease: Distal muscle weakness with sensory deficits
  • Myopathies (primary muscle disorders): Proximal muscle weakness without sensory deficit
  • Neuromuscular junction disease: Easy fatigability progressing to severe weakness and potential paralysis
  • Upper motor neuron disease: Weakness with increased muscle tone, hyper-reflexia and pathologic reflexes (Babinski, etc)
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8
Q

What are the four types of neuromuscular injury patterns?

A

Segmental demyelination
Axonal degeneration with muscle atrophy
Nerve regeneration and reinnervation
Muscle fiber damage

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9
Q

Describe the neuromuscular injury battery of SEGMENTAL DEMYELINATION–what causes an “onion bulb”?

A
  • Patchy involvement of internodes
  • Schwann cell death and myelin resorption
  • Endoneurial derived cells differentiate into replacement Schwann cells
  • Remyelination produces thinner, shorter internodes
  • “Onion bulb” formation occurs after repeated episodes of remyelination
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10
Q

Describe the neuromuscular injury of AXONAL DEGENERATiON

A

-Traumatic injury, disuse or intrinsic neuronal disease
Wallerian degeneration: Characteristic breakdown of distal axon
-Atrophy of muscle fibers:
-Decreased size and increased angularity (often triangular) of involved muscle fibers increase of endomysial tissue
–Myelin ovoids: abundant broken down myelin
—Preferential type II fiber atrophy in disuse

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11
Q

Describe the neuromuscular injury of NERVE/AXON REGENERATION AND REINNERVATION. What characterizes these?

A
  • Atrophied muscle fibers reinnervated by sprouting of new nerve endings from neighboring nerve fiber
  • Type grouping: clusters of single type of muscle fiber
    - —Phenotype of muscle fiber can change depending on nerve that innervates it
  • ———Thin axons and myelin sheaths characterize regenerative axons
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12
Q

Describe the neuromuscular injury of MUSCLE FIBER DAMAGE

A
  • Segmental Necrosis: Fragmentation of fibers and macrophage infiltration of fascicles
  • Regenerative changes: Internalized nuclei (enlarged; prominent nucleoli); Muscle fiber splitting and cytoplasmic basophilla
  • Vacuolization and intracytoplasmic deposits
  • Hypertrophy (increased fiber size) may occur in extreme exercise and some diseases
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13
Q

What are the types of peripheral nerve disease generally?

A 
Inflammatory neuropathies
Infectious polyneuopathies
Hereditary neuropathies
Acquired metabolic and toxic neuropathies
Traumatic neuropathies
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14
Q

Give an example of an inflammatory peripheral nerve disease. What is the histology?

A

Guillain-Barre Syndrome (GBS)–Acute and self-limited

  • Usually preceded by virus which is resolved prior to GBS
  • Ascending paralysis with minor sensory deficits
  • Isolated increase of CSF protein

Histology: Segmental demyelination, peripheral nerve inflammation
-T-cell destruction of peripheral nerve myelin sheath
-Circulating anti-myelin antibodies have been detected
Treatment: Plasmapheresis (Ab clearance)

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15
Q

Give an example of hereditary motor and sensory neuropathy type 1 (HMSN1).

A

Charcot-Marie-Tooth, hypertrophic
Characteristic nerve and muscle histology:
-Grouped muscular atrophy
-Segmental demyelination with prominent onion bulbs

  • Autosomal dominant: PMP-22 (myelin specific protein), chromosome 17
  • Onset in adolescence/early adulthood & slow progression; lower extremities only; normal life expectancy
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16
Q

What are the dental features of HMSN1/Charcot-Marie Tooth?

A

Damaged oral tissues and tongue due to biting without pain

Oral shields can be employed to reduce trauma

17
Q

Give an example of hereditary motor and sensory neuropathy type 2 (HMSN2).

A
  • Charcot-Marie-Tooth, neuronal (the HMSN1 is heterotrophic)
  • Autosomal dominant with genetic abnormality that differs from HMSN I
  • Rare segmental demyelination and onion bulbs
18
Q

Give an example of hereditary motor and sensory neuropathy type 3 (HMSN3).

A

Dejerine-Sotas

  • Autosomal dominant
  • Presentation in infancy with progression to severe neurological impairment
  • Prominent demyelination and onion bulbs (obvious palpable hypertonic nerves)
19
Q

What are some other etiologies of peripheral neuropathies?

A

Infectious – Varicella Zoster Virus/VZV (shingles)

Toxic/Metabolic:

  • Adult onset diabetes mellitus
  • -Neuropathies of Malignancy – Small cell carcinoma of the lung

Traumatic neuroma

20
Q

Give some examples of muscular diseases

A
  • Inflammatory Myopathies (polymyositis and dermatomyositis)
  • Muscular dystrophies – Hereditary myopathy
  • X-linked (Duchenne’s and Becker’s)
  • Autosomal dominant (Myotonic dystrophy)
  • Toxic myopathies (thyroid, EtOH and drugs)
21
Q

What is polymyositis?

A
  • inflammatory myopathy
  • Insidious onset, chronic course
  • Symmetric proximal weakness
  • HIV associated polymyositis (same course and histology)
22
Q

Describe dermatomyositis

A
  • inflammatory myopathy
  • Skin rash precedes weakness with acute progression
  • May be associated with connective tissue disorders or malignancy
23
Q

Dental implications of dermatomyositis

A

Gum margin involvement with capillary dilatation and inflammation
Late calcinosis develops in two-thirds of patients

24
Q

Describe the 2 types of X-linked muscular dystrophies

A

Both Equally effects type I and II fibers; Dense fibers

Duchenne’s M.D. (most severe)

  • Normal infancy with onset between 1-5 years of age and progression to death 20-25 years of age
  • Weakness in pelvic and shoulder muscles
  • Heart involvement with failure and arrhythmias
  • Mental impairment (etiology unclear)

Becker’s M.D. – Less severe: later onset, normal life exp, no heart involvement

25
Q

What is the Dystrophin gene and how is it related to muscular dystrophy?

A
  • Key component for muscle/tissue interaction
  • Prevents muscle damage during changes in size
  • Help maintain myocyte membranes during contraction
  • Mutations in gene cause both Duchenne’s and Becker’s but DIFFERENT AREAS OF GENE

Duchenne’s: Protein absent – frameshift with premature stop codon

Becker’s MD: Protein present but shortened with abnormal function
De novo mutations cause 1/3 of cases

26
Q

Describe the gene therapy used for Duchenne’s MD

A

Exon skipping: Can restore dystrophin expression with little loss of normal protein function
-Antisense oligonucleotides block inclusion of exon with premature stop codon

Many DMD mutations are deletions that are amenable to this type of therapy!!!
Other strategies: Induce utrophin expression; Stem cell (myoblast) trasplants

27
Q

Describe myotonic dystraphy

A

Autosomal dominant M.D.
Clinical features:
Myotonia: sustained involuntary muscle contraction
-Starts in hands and feet then progresses to face, etc.
-SM involvement, frontal balding, cardiomyopathy, gonadal atrophy, abnormal GTT and occasional dementia

  • Anticipation: Increasing severity with generations
  • Progression varies, but often prematurely fatal
  • Genetics: gene located on chr.19q13.2-13.3
  • Myotonin-protein kinase gene is site of mutation

Histology – Characteristic ring fiber; similar to Duchenne’s

28
Q

What are the dental features of hereditary myopathies?

A

Craniofacial morphology – Malocclusions

  • Posterior crossbite with anterior open bite
  • Weak masticatory muscles and hypotonic tongue contribute to developing these deformities during childhood development
  • Duchenne’s - Wide maxillary and mandibular dental arches
  • Myotonic Dystrophy - Deep and narrow palate
  • Chewing difficulties – Weak muscles of mastication mean that more and longer chewing necessary
29
Q

What are three diseases of the neuromuscular junction?

A

Myasthenia Gravis
Lambert-Eaton Syndrome
Botulism

30
Q

What are characteristics of Myasthenia Gravis?

A
  • Episodic weakness (often precipitated by medical illness)
  • often with ocular symptoms (diplopia, ptosis) followed by limb strength abnormalities
  • Sensory and autonomic function may be compromised
  • Tensilon test: improvesymptoms with administration of acetylcholinesterase inhibitor - diagnostic test!!!

Autoimmune disease:
Circulating antibodies to Ach receptor –> loss of receptors
-Antibody levels don’t correlate with disease activity
Immune complexes found on post-synaptic membranes

31
Q

What are the thymic abnormalities related to myasthenia gravis?

A

Thymic abnormalities related autoimmune activity
-65-75% show thymic hyperplasia
-15% develop thymoma
Thymectomy associated with clinical improvement in all

32
Q

What are the dental implications of myasthenia gravis?

A

Functional related problems:

  • Mastication problems – Flaccid tongue (furrowed appearance) and weak muscles
  • Chronic mucocutaneous candidiasis–Dysfunc. T-cells

Dental management;

  • Anti-cholinesterase therapy causes many problematic drug interactions and functional side effects
  • Exacerbation of weakness by a number of drugs
  • Anesthetic/muscle relaxant choice, careful with dose
  • aspiration risk during procedures – more salivation/ impaired swallowing
33
Q

What is Lambert Eaton Syndrome? How is it distinguished from Myasthenia Gravis?

A
  • Paraneoplastic process usually (Small cell CA)
  • Negative tensilon test and lack of AChR antibodies distinguish from Myasthenia Gravis
  • Proximal weakness and autonomic dysfunction
  • Histology is non-specific
34
Q

What does botulism do?

A

Botulinum toxin disrupts neurotransmitter release
Long lasting paralysis occurs
Can be used in some therapeutic applications

Organ Pathology Exam 1 (4 decks)

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