Peripheral Nerve Disorders Flashcards
1
Q
Peripheral Nerve Disorders
Subtypes
A
Peripheral nerve ⇒ neuropathy
Nerve root ⇒ radiculopathy
Lumbar or brachial plexus ⇒ plexopathy
Anterior horn ⇒ motor neuron disease
2
Q
Peripheral Nervous System
Basic Anatomy
A
- Consists of nerves and ganglia outside of the brain and spinal cord
- Peripheral nerves connected to spinal cord by two roots:
- Ventral root ⇒ motor
- Dorsal root ⇒ sensory
- Interconnects all other tissues with the CNS
- Innervates all voluntary muscles
- Transmits the sensory impulses to the whole body
- Individual nerve fibers ⇒ vary widely in diameter and may be heavily myelinated, lightly myelinated or unmyelinated
- Amount of myelin ∝ conduction speed
- Largely under conscious (cerebral) control
- Injury results in both sensory and motor loss
3
Q
Sensory Innervation
A
- A sensory nerve (afferent nerve) carries sensory information toward the CNS
- It is a bundle of nerve fibers coming from sensory receptors in the PNS
- Afferent nerve fibers leave the sensory neuron from the dorsal root ganglia of the spinal cord
- Large myelinated sensory fibers ⇒ vibration and proprioception
- Small myelinated and unmyelinated sensory fibers ⇒ pain and temperature
4
Q
Motor Innervation
A
-
Upper Motor Neuron
- Neuron in the motor cortex
- Travels down and decussates at the level of the medulla
- Travels down the spinal cord
-
Lower Motor Neuron
- Neuron in the spinal cord or cranial nerve of brainstem
- Travel to the skeletal muscle
5
Q
Motor Unit
A
A motor neuron and all the skeletal fibers it innervates.
- Groups of motor units work together to coordinate contraction of a single muscle
-
It is a functional unit made up of:
- Lower motor neuron
- Motor axon
- NMJs
- Muscle fibers innervated by the motor neuron
6
Q
Upper Motor Neuron
Signs
A
- Weakness
- Hyperreflexia
- Spasticity
- Stiffness
- Babinski sign
- Brisk jaw jerk
7
Q
Lower Motor Neuron
Signs
A
- Fasciculations
- Atrophy/muscle wasting
- Weakness
- Muscle cramps
- Loss of reflexes
8
Q
Disease Localization
A
Differentiating PNS from CNS disease
-
Weakness or sensory loss confined to one limb ⇒ peripheral nerve problem
- Associated pain in the extremity ⇒ ↑ likelihood of a peripheral process
- Localization less obvious when weakness/sensory loss involves > 1 extremity or when there is no associated pain or discomfort
- The patient approach will include taking a detailed hx including family hx of similar sx, time course of sx, and comorbidities (ex. DM)
- Complete neurologic exam will be extremely helpful
9
Q
Peripheral Nerve
Composition
A
Peripheral nerve is composed of:
- Motor axon/neuron
- Sensory axon/neuron
- Autonomic fibers
- Myelin
- Other supporting structures
10
Q
Peripheral Nerve
Characteristics
A
- Individual nerve fibers ⇒ vary widely in diameter and may be heavily myelinated, lightly myelinated or unmyelinated
- Amount of myelin ∝ conduction speed
- Myelin made by Schwann cells
- Distance b/t nodes of Ranvier determines conduction rate
- Largely under conscious (cerebral) control
- Injury results in both sensory and motor loss
11
Q
Peripheral Nerve Damage
A
-
Segmental demyelination
- Diseases primarily affect Schwann cells ⇒ loss of myelin
-
Nerve injury/transection
- Primary destruction of the axon ⇒ secondary disintegration of its myelin sheath
- Results in axonal degeneration
- Distal portion ⇒ Wallerian degeneration
- Proximal portion ⇒ retrograde degeneration
- Begins in the periphery and proceeds back toward the cell body ⇒ “dying back“
- Cell body may become chromatolytic
- If process reversed early phases, some regeneration may be possible
12
Q
Axonal Injury
A
Traumatic transection of a nerve
-
Distal portion of the nerve fiber degenerates ⇒ Wallerian degeneration
- Axons begin to break down
- Schwann cells begin to catabolize myelin and later engulf axon fragments, forming myelin ovoids
- MΦ recruited and phagocytose axonal and myelin-derived debris
-
Proximal portion of severed nerve degenerates ⇒ retrograde degeneration
- Degenerative changes involving only the most distal two or three internodes
- Proximal stump then undergoes regenerative activity
- Regenerated fiber has shorter internodes
13
Q
Segmental Demyelination
A
- Selective loss of individual myelin internodes with preservation of the axon
- Process affects some Schwann cells and their corresponding internodes while sparing others
- Disintegrating myelin is engulfed initially by Schwann cells and later by MΦ
- After segmental demyelination, Schwann cells can proliferate and remyelinate
- Example: Guillain-Barré Syndrome
14
Q
Regenerative Processes
A
-
Axonal Sprouting
- After axonal damage, the axon may sprout from the distal end
- Regenerating axons re-grow at ~ 1 mm/day
-
Remyelination stimulated by denuded axon
- Segmentally demyelinated axons may remyelinate ⇒ shorter internodes = slower conduction
- Axonal sprouts will be re-myelinated by surviving Schwann cells
- Remyelination may restore some function
- Repeated episodes of demyelination and remyelination → accumulation of layers of Schwann cell processes
- Onion Bulb: a single thinly myelinated axon surrounded by concentrically arranged Schwann Cells and redundant BM
15
Q
Neurodiagnostic Testing
A
Electromyography (EMG) and Nerve conduction studies (NCS)
- Most common diagnostic tests for dx of nerve and muscle disease after hx and exam
- Both are complementary and are always performed together during the same setting
16
Q
Nerve Conduction Studies (NCS)
A
Measure the ability of sensory and motor fibers to conduct an action potential
Used mainly for eval of paresthesias and/or weakness of arms and legs
-
Axonal injury/neuropathy
- ↓ amplitude of AP
- Mild slowing
- Can see mix of both
-
Demyelination neuropathy
- Conduction block (failure of AP to propogate)
- Slow conduction
- Amplitude of AP may be normal or reduced
17
Q
Electromyography (EMG)
A
Measures muscle response or electrical activity in response to nerve stimulation of the muscle
Used to determine NMJ abnormalities, myopathy, and denervation
-
Increased insertion activity
- Denervation ⇒ will fire spontaneously as a “Fibrillation potential”
- Polymyositis
-
Decreased insertional activity
-
Myopathy ⇒ loss of response of motor units
- Small motor units
- Early recruitment of other motor units
- Muscle is replaced by fat
-
Myopathy ⇒ loss of response of motor units
- Muscle fibers s/p denervation and reinnervated ⇒ very large due to reorganization and formation of large motor units
18
Q
Peripheral Nerve Biopsy
A
- Used when the pathology is in question and when therapy is contemplated
- Superficial sensory branches of the sural or radial nerves are often sampled and examined pathologically
19
Q
Peripheral Neuropathy Patterns
A
Patterns of peripheral neuropathy aids in clinical dx and finding underlying pathologic processes:
- Mononeuropathy
- Mononeuropathy Multiplex
- Polyneuropathy
20
Q
Focal Neuropathies
(Mononeuropathies)
A
- Typically have damage to a single nerve
- Etiologic agents are focal ⇒ process tends to be asymmetric
- Classic cause is vasculitis ⇒ produces discrete infarctions in nerve trunks
- NO distal-proximal gradient b/c an individual nerve trunk is affected
21
Q
Median Nerve
A
Responsible for:
- Flexion of the thumb, index, and middle fingers
- Wrist flexion
- Thumb opposition
- Forearm protonation
- Hand abduction
22
Q
Median Nerve Entrapment
(Carpal Tunnel Syndrome)
A
Secondary to compression of the median nerve as it passes through the carpal tunnel
Most common nerve entrapment
- Due to any condition that causes decreased space within the carpal tunnel
- Tissue edema, pregnancy, inflammatory arthritis, hypothyroidism, amyloidosis acromegaly, DM, and excessive repetitive motions of the wrist
- Pain primarily at the wrist, may radiate to forearm, arm, or shoulder
-
Sensory findings: paresthesia and sensory loss in the thumb, index and lateral half of ring fingers of affected hand
- Often noted more at night
- Motor findings: Weakness of thumb abduction and atrophy of the thenar eminence
-
Diagnostic signs:
- Phalen’s Sign: elicited when wrist flexion produces paresthesias in the median nerve distribution
- Tinel’s Sign: present when tapping over the median nerve at the wrist elicits paresthesias in the median nerve distribution
- NCS: focal slowing or conduction block of median nerve fibers
- Treatment: wrist splints in mild cases and surgical decompression in severe cases
23
Q
Ulnar Nerve
A
Responsible for:
- Wrist flexion
- Flexion of 4th and 5th digits
- Thumb adduction
- Finger abduction and adduction
24
Q
Ulnar Neuropathy
(Cubital Tunnel Syndrome)
A
Nerve entrapment due to compression of the ulnar nerve in the cubital tunnel at the elbow.
- Sensory signs: numbness of the little finger and half of the ring finger
- Motor signs: decreased grip and problems with finger dexterity
- NCS: Slow conduction velocity at the elbow, or conduction block
- Treatment: avoidance of behaviors involving leaning on elbows, elbow pads or surgical decompression in severe cases
25
Q
Radial Nerve
A
Responsible for:
- Supination of forearm
- Brachioradialis reflex
- Extension of fingers, thumb, wrist, and elbow
26
Q
Radial neuropathy
“Saturday Night Palsy”
A
Results from compression of the radial nerve at the radial/spiral groove.
- Classic case seen with sleeping with arm draped over a chair
- Can also be seen with humerus fracture or other insult
- Sensory sx: sensory loss over lateral dorsal hand
- Motor sx: wrist drop, finger drop, weakness of supination, mild elbow flexion weakness
- Treatment is supportive with generally spontaneous recovery
27
Q
Peroneal (Fibular) Nerve
A
-
Deep peroneal nerve
- Ankle and toe dorsiflexion
- Foot eversion
-
Superficial peroneal nerve
- Sensory over anterior and lateral lower leg
28
Q
Peroneal Neuropathy
A
Results from compression of the peroneal nerve as it wraps around the fibular head.
- Often results from leg crossing, prolonged bedrest, knees casts, fibular fractures
- Motor sx: weakness of toe and foot dorsiflexion and foot eversion
- Sensory sx: sensory loss over the dorsum of the foot and lateral distal lower extremity
- NCS: Slow conduction velocity at fibular head
- Management is usually supportive with removing cause of compression
29
Q
Lateral Femoral Cutaneous Nerve
A
Provides sensation to the:
- Anterior thigh
- Knee
- Upper part of lateral thigh
30
Q
Lateral Femoral Cutaneous Neuropathy
(Meralgia Paresthetica)
A
Results from entrapment of the lateral femoral cutaneous nerve as it passes under the inguinal ligament.
- Causes include tight clothing, obesity, and pregnancy
- Presents with paresthesias in the lateral thigh
- NCS/EMG not helpful
- Tx: supportive, meds
34
Q
Polyneuropathy
Clinical Manifestations
A
- Length dependent sensory loss and weakness
- Reflexes are decreased
- Autonomic dysfunction can occur in severe cases
- Sx may be variable
36
Q
Diabetic Polyneuropathy
A
- Most common cause of neuropathy
- Most common complication of DM
- Involves peripheral and autonomic nervous system
- Has a distal-proximal gradient
- Duration and severity of hyperglycemia ⇒ crucial risk factor for development of diabetic neuropathy
- Microvascular injury to blood vessels that supply the nerve
- Prominent axonal degeneration w/ myelin debris, distal > proximal
-
Sx vary depending on areas affected:
- Sensitive to touch
- Pain
- Anesthesia
- Burning sensation
- Muscle weakness or wasting
- Ataxia
- Treatment includes better glycemic control, gabapentin, pregabalin, SSNRI
39
Q
Guillain-Barre Syndrome (GBS)
(“Acute Inflammatory Demyelinating Polyneuropathy (AIDP)”
A
Severe ascending, symmetric weakness with areflexia.
- Rapidly progressive acute segmental demyelination
- ± Preceding illness
- Distal to proximal gradient
- Begins with distal paresthesias, pain in back/neck, and leg weakness
- ± Cranial nerve involvement
- ± Secondary respiratory failure
- ± Autonomic instability ⇒ arrythmia and BP changes
- Progresses for up to several weeks
- ↑ CSF protein but normal WBC count (albumnio-cytological dissociation)
- NCS/EMG: slow conduction velocities or conduction block
- Management: Plasmapheresis or IVIG ⇒ slows progression
46
Q
Charcot Marie Tooth (CMT)
A
Hereditary motor and sensory neuropathy
-
Clinical manifestations:
- Foot drop
- Claw toe / hammer toes
- Pes cavus (high arch of foot)
- Wasting of hands, feet, and distal leg muscles
- Mild sensory loss
- Enlarged nerves
- Pathology: demyelination and onion bulbs
- Multiple variants with different transmission patterns: autosomal dominant, autosomal recessive, or X-linked
52
Q
Radiculopathy
Overview
A
- Due to damage to a nerve root
- Disc herniation is the most common cause
- Characterized by sensory complaints in a dermatomal distribution and weakness in the muscles innervated by the root
- If nerve root involved in a reflex, reflex may be decreased
- Pain
- NCS/EMG: sensory AP’s are normal, EMG w/ fibrillations in paraspinal muscles (acute)
- Treatment:
- Supportive - PT, pain management
- Surgery
60
Q
Plexopathy
A
- Disorder affecting a network of nerves, blood vessels, or lymph vessels
- Brachial or lumbosacral plexus
- Sx include pain, loss of motor control, atrophy and sensory deficits
- The entire plexus, or just portions may be involved
61
Q
Brachial Plexopathy
A
- Can be d/t compression, transection, ischemia, inflammation, metabolic abnormalities, neoplasia, radiation therapy, trauma, burns, postoperatively, autoimmune or post-infectious, or direct infiltration
- Muscle weakness, atrophy, sensory loss, and pain
- Acute onset ⇒ pain in the shoulder and upper arm
- Insidious onset ⇒ progressive pain, evolving numbness, weakness of selected muscle groups
62
Q
Lumbosacral Plexopathy
Clinical Manifestations
A
Pattern of weakness/numbness helps localize lesion:
-
Lumbar plexus:
- Weakness of hip flexion and adduction and/or knee extension
- Sensory disturbance in anterior thigh and medial leg
-
Lumbosacral trunk and upper sacral plexus:
- Foot drop, flail foot, weakness of knee flexion or hip abduction
- Sensory disturbance in leg, dorsum of foot, posterior thigh, perineum
64
Q
Motor Neuron Disease
A
Neurodegenerative disorders that selectively affect motor neurons of the spinal cord
- ALS is most common
- Can have UMN + LMN signs or just LMN
- Progressive
65
Q
Amyotrophic Lateral Sclerosis
(ALS)
A
Neurodegenerative disease of the upper and lower motor neurons.
- Onset 55-75 years
- UMN dysfunction ⇒ increased tone, spasticity, hyperreflexia and positive Babinski
- LMN dysfunction ⇒ atrophy, weakness, fasciculation and loss of reflexes
- Extraocular muscles and sensation usually spared
- Late in course, spasticity may occur
- Bulbar weakness ⇒ dysarthria, dysphagia
- Pts present with asymmetric distal weakness
- Usually weakness starts in one region then spreads to adjacent regions then spreads to contralateral limb
- Pts often die with respiratory insufficiency or aspiration pneumonia
- Management: Supportive (multidisciplinary clinics), Riluzole (may prolong survival)
