Peripheral Nerve Diseases; Anatomy, Physiology and Pathophysiological Process
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Peripheral Nerve Diseases;
Anatomy, Physiology and Pathophysiological
ProcessBerrin Aktekin
Yeditepe University Department of Neurology
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Functional Organization of the PNS
Figure 14.1
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Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve
A nerve is composed of numerous nerve fibers
Figure 14.2
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Spinal Nerves
31 pairs – contain thousands of nerve fibers
Connect to the spinal cordNamed for point of issue from the spinal cord- 8 pairs of cervical nerves (C1 – C8)- 12 pairs of thoracic nerves (T1 – T12)- 5 pairs of lumbar nerves (L1 – L5)- 1 pair of coccygeal nerves (Co1)
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Spinal Nerves Posterior View
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Spinal Nerves
Connect to the spinal cord by the dorsal root and ventral root
Dorsal root – contains sensory fibers- cell bodies located in the dorsal root ganglion
Ventral root – contains motor fibers arising from anterior gray column
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Spinal Nerves
Branch into dorsal ramus and ventral ramus- dorsal and ventral rami contain sensory and motor fibers
Rami communicantes – connect to the base of the ventral ramus- lead to the sympathetic chain ganglia
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Spinal Nerves
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Innervation of the Back
Dorsal rami – innervate back muscles- follow a neat, segmented pattern- innervate a horizontal strip of muscle and skin (in line with emergence point from the vertebral column)
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Innervation of the Back
Figure 14.7b
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Innervation of the Anterior Thoracic and Abdominal Wall
Thoracic region – ventral rami arranged in simple, segmented pattern
Intercostal nerves supply intercostal muscles, skin, and abdominal wall- each gives off lateral and anterior cutaneous branches
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Introduction to Nerve Plexuses
A network of nervesVentral rami (except T2 – T12)- branch and join with one another- form nerve plexuses in the cervical, brachial, lumbar, and sacral regions- primarily serve the limbs- fibers from ventral rami crisscross
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Motor Unit=Myotom
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The Cervical Plexus
Buried deep in the neck under the sternocleidomastoid muscle
Formed by ventral rami of first 4 cervical nerves (C1 – C4)
Most are cutaneous nervesSome innervate muscles of the anterior neck
Phrenic nerve – major nerve
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The Brachial Plexus and Innervation of the Upper Limb
Brachial plexus lies in the neck and axillaFormed by ventral rami of C5 – C8
Cords give rise to main nerves of the upper limb
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The Brachial PlexusFig 14.9a
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Lumbar Plexus and Innervation of the Lower Limb
Arises from L1 – L4Smaller branches innervate the posterior abdominal wall and psoas muscle
Main branches innervate the anterior thigh- femoral nerve innervates anterior thigh muscles- obturator nerve innervates adductor muscles
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The Lumbar Plexus
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Sacral PlexusArises from spinal nerves L4 – S4Caudal to the lumbar plexusOften considered with the lumbar – lumbosacral plexus
Sciatic nerve – largest nerve- 2 nerves in one sheath: Tibial nerve – innervates most of the posterior lower limb;Common fibular (peroneal) nerve – innervates muscles of the anterolateral leb
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The Sacral Plexus
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Autonomic Nervous System
General visceral motor part of the PNSHas 2 divisions (with opposite effects):- Parasympathetic: ‘housekeeping’ activities (rest and digest)- Sympathetic: extreme situations (fight or flight)
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Sensory SystemFive sense !!!Peripheral Sensory System
SpinothalamicDorsal Column
Cortical-integrative Sensory System
Visceral Sensory System
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Innervation of the Skin: Dermatomes
Dermatome – an area of skinInnervated by cutaneous branches of a single spinal nerve
Upper limb – skin is supplied by nerves of the brachial plexus
Lower limb:Lumbar nerves – anterior surfaceSacral nerves – posterior surface
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Peripheral Sensory System
Spinothalamic system-Cutaneous Pain- Temperature Light touch/pressure
Dorsal Column-Medial Lemniscal System-Proprioception
Vibration Position
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Spinothalamic system
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Dorsal Column-Medial Lemniscal System-
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Peripheral Sensory Receptors
Most fit into 2 main categories:1. free nerve endings of sensory neurons
- monitor general sensory information such as touch, pain, pressure, temperature, and proprioception
2. complete receptor cells – specialized epithelial cells or small neurons that transfer sensory information to sensory neurons- monitor most special sensory information such as taste, vision, hearing, and equilibrium
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Sensory Receptors of the PNS
Also classified according to:a) Location – based on body location or location of stimuli to which they respondb) Type of stimulus detected – kinds of stimuli that most readily activate themc) Structure – divided into 2 broad categories free or encapsulated nerve endings
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Classification by Location Exteroceptors – sensitive to stimuli arising from outside the body
- located at or near body surfaces- include receptors for touch, pressure, pain, temperature, and most receptors of the special sense organs
Proprioceptors – monitors degree of stretch and sends input on body movements to the CNS- located in musculoskeletal organs such as skeletal muscles, tendons, joints, and ligaments
Interoceptors (visceroceptors) – receive stimuli from internal viscera (digestive tube, bladder, lungs)- monitor a variety of stimuli such as changes in chemical concentration, taste stimuli, stretching of tissues, and temperature- activation causes visceral pain, nausea, hunger, or satiety
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Classification by Stimulus Detected
Mechanoreceptors – respond to mechanical forces- such as touch, pressure, stretch, vibrations, and itch
Thermoreceptors – respond to temperature changes
Chemoreceptors – respond to chemicals in solution (molecules tasted or smelled) and to change in blood chemistry
Photoreceptors in the eye – respond to lightNociceptors – respond to harmful stimuli that result in pain (noci = harm)
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Peripheral NeuropathyWeakness or sensory loss or both based on nerve injury
Generally distal symptoms, legs before arms, but there are exceptions
Mostly symmetrical but can be asymmetric or focal
Small fiber - diminished pain/temperature, preserved strength, reflexes
Large fiber - loss position, vibration touch/pressure, areflexia
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Symptoms of Peripheral Neuropathies
Symptoms are related to the type of affected nerve and may be seen over a period of days, weeks, or yearsMuscle weakness is the most common symptom of motor nerve damage
Sensory nerve damage causes a more complex range of symptoms because sensory nerves have a wider, more highly specialized range of functions
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Symptoms of Peripheral NeuropathiesSx’s of autonomic nerve damage depend upon the affected organs/glands
Can become life threatening and may require emergency medical care
Common symptoms of autonomic nerve damage include:
unable to digest food easily an inability to sweat normally, which may lead to
heat intolerance a loss of bladder control, which may cause
infection or incontinence an inability to control muscles that expand or
contract blood vessels to maintain safe blood pressure levels
organ failure may occur.
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Sensory symptoms Start in feet, move proximally Hand sxs appear when LE sxs up to
knees Positive Pins and needles Tingling Burning
Negative Numbness Deadness “Like I’m walking with thick socks on”
Symptoms of Peripheral Neuropathies
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MotorWeakness first in feetTrippingTurn ankles
Progress to weakness in handsTrouble opening jarsTrouble turning key in lock
Symptoms of Peripheral Neuropathies
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Polyneuropathy: SignsDistal sensory loss
Large fiberloss position, vibration touch/pressure, areflexia
Small fiberdiminished pain/temperature, preserved strength, reflexes
Distal weakness and atrophyDecreased or absent reflexes
Ankle jerks lost first
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The 3 questions of clinical neurology… 1. Where is the lesion? 2. What is the etiology? 3. What is the treatment?
www.ama-assn.org/ ama/pub/category/7172.html
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The patterns of peripheral neuropathy
www.ama-assn.org/ ama/pub/category/7172.html
• Mononeuropathy?
• Polyneuropathy? multiple nerves
contiguous typically length dependent
(“stocking-glove”)
Polyneuropathy is common! 2.4% (8% over 55 yr)
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Mastering polyneuropathy#1. Where is the injury?The syndrome depends on: what modalities are injured, what fibers are injured, whether axon or myelin (or both) injured.
#2. What is the etiology?Tricky – hence an approach necessary at the bedside.
#3. What is the treatment?Depends on reversing the underlying cause.
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http://www.neuro.wustl.edu/neuromuscular/pathol/nervenl.htmhttp://fulton.edzone.net/cites/winkler-science/team1/chap8.html
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The clinical effect of a polyneuropathy depends on 1) what modalities involved 2) what fibers are effected 3) whether the injury is axonal or demyelinating.
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Loss of function“- symptoms”
Disturbed function“+ symptoms”
Motor nerves WastingHypotoniaWeaknessHyporeflexiaOrthopedic deformity
FasiculationsCramps
The clinical response to motor nerve injury
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www.neuro.wustl.edu/neuromuscular/pics/people/patients/Hands/handatrophymnd3.jpg
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Loss of function“- symptoms”
Disordered function“+ symptoms”
Sensory “Large Fiber”
↓ Vibration↓ ProprioceptionHyporeflexiaSensory ataxia
Paresthesias
Sensory “Small Fiber”
↓ Pain↓ Temperature
DysesthesiasAllodynia
The clinical response to sensory nerve injury
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Loss of function“- symptoms”
Disturbed function“+ symptoms”
Autonomic nerves ↓ SweatingHypotensionUrinary retentionImpotenceVascular color changes
↑ Sweating Hypertension
The clinical response to autonomic nerve injury
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http://www.neuro.wustl.edu/neuromuscular/nother/skel.html#nosteo
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The two types of peripheral neuropathies:axonopathies and myelinopathies
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From Kumar: Robbins and Cotran: Pathologic Basis of Disease, 7th ed.
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Using nerve conduction studies in polyneuropathy
= Slow!
= Low!
= Slow!
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Normal Nerve Axonal degeneration
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Wallerian Degeneration
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Axonopathies
By far the majority of the toxic, metabolic and endocrine causes
NCVs: CMAPs ↓ 80% lower limit of normal w/o or min velocity or distal motor latency change.
Legs>> arms.EMG: Signs of denervation (acute, chronic) and reinnervation
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Segmental Demyelination
http://www.neuro.wustl.edu/neuromuscular/pathol
Normal
Demyelination
Normal
Demyelination
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Question #2. What is the etiology?Only a limited number of ways a peripheral nerve can react to injury, thus a multitude of different etiologies can cause similar effects…
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Problem: The multitude causes of peripheral neuropathy!!!
Inherited: e.g. Charcot-Marie-Tooth disease (HMSN)Infectious: e.g. LeprosyInflammatory: e.g. Guillain Barre syndrome (AIDP)Neoplastic: e.g. Monoclonal gammopathyMetabolic: e.g. DiabetesDrug: e.g. VincristineToxic: e.g. Ethanol
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Peripheral Neuropathy in summary…1. Patterns: mononeuropathy, mononeuropathy multiplex or polyneuropathy – focal, multifocal or diffuse
2. “Signature” manifestations of a polyneuropathy depend on what modalities affected (motor, sensory, autonomic) and whether it is axonal or demyelinating.
3. Examination, NCS/EMG & biopsy can discriminate axonopathy from myelinopathy
4. The multiple potential etiologies of polyneuropathy are manageable recognizing patterns of disease by the 6 Ds