Download Motor Disorders Sites of Damage in Nerve and Muscle Site Disorder

Neurophysiological Basis of Movement
World VI:
Motor Disorders
Lecture 30: Peripheral Muscular
and Neurological Disorders
Sites of Damage in Nerve and Muscle
Site
Disorder
Neuron cell body
Root
Axon
Demyelination
Neuromuscular synapse
Muscle
ALS (Lou Gehrig’s disease)
Cervical or lumbar radiculopathy
Axonal neuropathy
Guillain-Barré syndrome
Myasthenia gravis
Muscular dystrophy
Muscular Dystrophies
 Genetic diseases: progressive weakness and
degeneration of skeletal muscles
 Duchenne and Becker dystrophy—1 in 3,500 to
5,000 births
 Mostly males are affected
Muscular Dystrophies:
Duchenne Dystrophy
 Mutation of a gene responsible for dystrophin, a
protein involved in maintaining integrity of
muscle fibers
 Clinical symptoms at 2 to 6 years; all muscles are
affected
 Late to walk; waddling, unsteady gait
 Respirator dependence by the age of 20
Muscular Dystrophies:
Becker Dystrophy
 Similar to Duchenne dystrophy; mutation of a
gene responsible for dystrophin
 Clinical symptoms appear at adolescence
 Slower disease progression; longer life
expectancy
Muscular Dystrophies:
Myotonic Dystrophy
 Most common adult form of muscular dystrophy
 Myotonia: prolonged episode of muscle activity
after its voluntary contraction
 Commonly in finger and facial muscles
 High-stepping, floppy-footed gait
 Long face; drooping eyelids
Myotonic Discharge
Stiff Person Syndrome
 Excessive motoneuron excitation
 Starts at 30 to 60 years of age
 Leads to boardlike rigidity of trunk muscles
Stiff Person Syndrome
Continuous Muscle Fiber
Activity Syndromes
Tetanus (induced by tetanus toxin):
 The toxin blocks postsynaptic inhibition
at the spinal level.
 EMG bursts can be stopped by
neuromuscular or peripheral nerve block.
 Discharges are attenuated during sleep
and under general or spinal anesthesia.
Continuous Muscle Fiber
Activity Syndromes
Stiff person syndrome:
 Excessive motoneuron excitation
 Coactivation of agonist–antagonist muscles
 Proximal muscles are particularly involved
Neuromyotonia:
 Continuous activity of single muscle fibers
 Seen at rest and on the background of vol. activation
 Defect probably in the motor axon terminals
Neuromyotonia
Small potentials on the background on voluntary
activation
Myasthenia Gravis
 Disorder of transmission at the neuromuscular synapse
 Clinical signs:
– fatigue, exhaustion, muscle atrophy
– any muscle(s) can be affected, but especially eye, face,
lip, tongue, throat, neck, and limb muscles
– ocular signs (eyelid droop; inability to open one eye)
– facial weakness (stiffness of the face; difficulties with
chewing, swallowing, laughing, and speech [dysarthria])
– may lead to ventilatory insufficiency and death
Myasthenia Gravis: Epidemiology
 3 to 4 new cases per million annually
 Prevalence: 60 cases per million
 Can start at any age
 Women are affected 2:1 over men
 Death rate in the 1930s was 40%; death rate in the
1970s–1980s was 7%
Myasthenia Gravis: Physiology
 Autoimmune process (the body produced
antibodies to ACh receptors)
 Reduction of ACh receptors
 Reduction of postsynaptic potentials
Myasthenia Gravis: Increased Duration
of Action Potentials in the Muscle
Myasthenia Gravis: Treatment
 ACh-esterase inhibitors (neostigmine, distigmine)
 Thymectomy to suppress autoimmune processes
 Plasmapheresis to remove autoimmune antibodies
 Side effects with any treatment
Peripheral Neuropathies:
Mononeuropathies
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Slowed conduction in a single nerve
Reduced amplitude of motor and/or sensory potentials
Signs of denervation
Carpal tunnel syndrome: entrapment of the median nerve
at the wrist
Ulnar nerve can be entrapped near the elbow
Brachial plexus lesions: mostly seen in muscles innervated
by median and ulnar nerves
Peroneal: peroneal pressure palsy
Tibial: tarsal tunnel syndrome
Sciatic
Carpal Tunnel Syndrome
Peripheral Neuropathies:
Multiple Mononeuropathies
 Diabetes mellitus
 Polyarteritis nodosa (connective tissue
disorder, vasculitis)
 Leprosy
Diabetes (Diabetes Mellitus):
Impaired Ability to Metabolize Glucose
 Total number of cases in the U.S.: 16 million
 Yearly increase: 650,000 new cases
 Long-term complications:
– Peripheral sensory neuropathy
– Peripheral motor neuropathy
– Loss of autonomic nerve function
– Atrophy of peripheral tissues
Diabetes
Clinically apparent peripheral nerve damage occurs:
 In 25% of patients after 10 years
 In 50% of patients after 20 years
Consequences:
 Loss of balance and coordination
 Increased probability of falls, fractures,
bruises, etc.
Diabetes
Effects of muscle vibration on posture:
 Lower during vibration of Achilles tendon
 Higher during vibration of hamstrings
Reorganization of postural control: switch
to alternative sources of information
Consequence of Diabetes:
Atrophy of Peripheral Tissues
 Is it a consequence of inadequate blood supply?
 Is it a consequence of abnormal pressure
distribution with foci of high pressure?
 Studies by the group of Peter Cavanagh
Diabetes
VIF
VIF
VIF
VIF
Peripheral Neuropathies:
Polyneuropathies
 May be associated with demyelinating
neuropathies
 Guillain-Barré syndrome: reduced recruitment;
conduction block; may result in permanent
axonal loss
 Chronic inflammatory demyelinating
polyneuropathy: common recovery, but nerve
conduction velocity may remain slow
Peripheral Neuropathies:
Polyneuropathies
 Axonal neuropathies (mostly of toxic origin)
 Neuronal degenerations:
– Amyotrophic lateral sclerosis (Lou Gehrig’s
disease)
– Poliomyelitis (enterovirus destroying anterior
horn cells; EMGs show chronic denervation;
may lead to weakness and pain—a postpolyo
syndrome)
ALS
 20,000 Americans have ALS (one in 15,000).
 5,000 people in the United States are diagnosed with
ALS each year.
 Men are affected more often than women.
 ALS most commonly strikes people between 40 and
60 years of age.
 About 5 to 10 percent of all ALS cases are inherited.
 About 20 percent of all familial cases result from a
specific genetic defect: mutation of superoxide
dismutase 1 (SOD1).
ALS
 The earliest symptoms may include twitching,
cramping, or stiffness of muscles; muscle weakness
affecting an arm or a leg; slurred and nasal speech;
or difficulty chewing or swallowing.
 Patients have increasing problems with moving,
swallowing (dysphagia), and speaking or forming
words (dysarthria).
 Patients have tight and stiff muscles (spasticity)
and exaggerated reflexes (hyperreflexia).