peripheral nerve diseases; anatomy, physiology and pathophysiological process

Peripheral Nerve Diseases;

Anatomy, Physiology and Pathophysiological

ProcessBerrin Aktekin

Yeditepe University Department of Neurology

Functional Organization of the PNS

Figure 14.1

Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve

A nerve is composed of numerous nerve fibers

Figure 14.2

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)

Spinal Nerves Posterior View

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

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

Spinal Nerves

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)

Innervation of the Back

Figure 14.7b

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

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

Motor Unit=Myotom

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

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

The Brachial PlexusFig 14.9a

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

The Lumbar Plexus

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

The Sacral Plexus

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)

Sensory SystemFive sense !!!Peripheral Sensory System

SpinothalamicDorsal Column

Cortical-integrative Sensory System

Visceral Sensory System

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

Peripheral Sensory System

Spinothalamic system-Cutaneous Pain- Temperature Light touch/pressure

Dorsal Column-Medial Lemniscal System-Proprioception

Vibration Position

Spinothalamic system

Dorsal Column-Medial Lemniscal System-

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

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

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

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)

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

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

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.

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

MotorWeakness first in feetTrippingTurn ankles

Progress to weakness in handsTrouble opening jarsTrouble turning key in lock

Symptoms of Peripheral Neuropathies

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

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

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)

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.

http://www.neuro.wustl.edu/neuromuscular/pathol/nervenl.htmhttp://fulton.edzone.net/cites/winkler-science/team1/chap8.html

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.

Loss of function“- symptoms”

Disturbed function“+ symptoms”

Motor nerves WastingHypotoniaWeaknessHyporeflexiaOrthopedic deformity

FasiculationsCramps

The clinical response to motor nerve injury

www.neuro.wustl.edu/neuromuscular/pics/people/patients/Hands/handatrophymnd3.jpg

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

Loss of function“- symptoms”

Disturbed function“+ symptoms”

Autonomic nerves ↓ SweatingHypotensionUrinary retentionImpotenceVascular color changes

↑ Sweating Hypertension

The clinical response to autonomic nerve injury

http://www.neuro.wustl.edu/neuromuscular/nother/skel.html#nosteo

The two types of peripheral neuropathies:axonopathies and myelinopathies

From Kumar: Robbins and Cotran: Pathologic Basis of Disease, 7th ed.

Using nerve conduction studies in polyneuropathy

= Slow!

= Low!

= Slow!

Normal Nerve Axonal degeneration

Wallerian Degeneration

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

Segmental Demyelination

http://www.neuro.wustl.edu/neuromuscular/pathol

Normal

Demyelination

Normal

Demyelination

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…

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

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