sgsnyc peripheral nerve disorders I
Terms in this set (106)
Describe what happens in an action potential (4 steps)
1. depolarization of Na channel leads to opening
2. influx of Na into the cell causing further depolarization
3. closing of Na channel and delayed opening of K channels leading to outflux of K and hyperpolarization
4. closing of K channel with repolarization thru 3Na/2K-ATPase pumping Na out of the cell and K into the cell
What's the resting membrane potential? What does it depolarize to in an action potential?
Resting: -60 mV
Depolarization: 30 mV
Name the different types of nerve fibers (I-
IV), their cutaneous classification, size and conduction velocity, myelination, and function
Name the different types of nerve fibers (A-C), their cutaneous classification, size and conduction velocity, myelination, and function
Name 4 skin receptor types. What is their location, adaptation rate, and quality?
Meissner's corpuscle: superfical, rapid, touch
Merkel's cell: superficial, slow, steady indentation
Parcinian corpuscle: deep, rapid, flutter
Ruffinian corpuscle: deep, slow, vibration
Imagine the 4 skin receptor types
Name, again, the types of sensory axons, with classification in motor nerves, cutaneus nerves, size & conduction velocity, myelin + or -, and function
I = Aalpha - 20mm, 100m/s, +, Ia: muscle spindles, Ib: Golgi tendon organs
II = Abeta - 10mm, 60m/s, +, muscles spindles, cutaneous receptors (Meissner, Merkel, Pacinian, Ruffinian)
III = Adelta - 5mm, 20m/s, +/-, fast localizable pain, temperature
IV = C/wide-dynamic, 1mm, 1m/s, -, slow, poorly localized "burning" pain
Picture the organization of a peripheral nerves
What roots form the cervical plexus?
Name the nerves of the cervical plexus (4)
lesser occipital, greater auricular, transverse cervical, supraclavicular
What muscles are innervated by the cervical plexus (5)?
high cervical paraspinals
picture the scalene muscles. what's their function?
it's on the side of the neck, there are three portion, the anterior one is anterior to the brachial plexus, the middle and posterior portion are posterior to the brachial plexus.
They originate from the transverse processes of C2-C7, and insert at the first or second rib.
Function: head tilt
what are the infrahyoid muscles? What is their function?
sternohyoid, sternothyroid, thyrohyoid and omohyoid muscles.
All of the infrahyoid muscles are innervated by the ansa cervicalis from the cervical plexus (C1-C3) except the thyrohyoid muscle, which is innervated by fibres only from the first cervical spinal nerve travelling with the hypoglossal nerve
function to depress the hyoid bone and larynx during swallowing and speech
What is the usual cause of injury to the cervical plexus?
What are signs of mild diaphragm weakness, and severe weakness?
mild: orthopnea, DOE
severe: severe dyspnea, inability to cough
What are the roots of the brachial plexus?
What are causes of brachial plexopathy (5)
immune-mediated brachial plexus neuropathy (Parsonage-Turner)
perioperative plexopathies (open heart surgery, thoracotomy)
Describe the differences between brachial plexopathy caused by neoplasm vs radiation induced brachial plexopathy: preferential involvement, symptoms, EMG findings in radiation induced brachial plexopathy
neoplasm: lower trunk, painful, pain and paresthesias early, sensory and motor loss later
radiation: upper trunk, painless, myokymic discahrges in EMG are strongly suggestive, months to years after radiation, due to microvascular changes and tissue fibrosis
What are the three types of thoracic outlet syndrome?
neurological, arterial, venous
What happens in neurological thoracic outlet?
fibrous band from C7 transverse process to 1st thoracic rib compresses lower trunk supplied by C8-T1 -> medial forearm pain and hand weakness & atrophy
What is the cause of arterial thoracic outlet syndrome? And what are the symptoms?
cervical rib compresses subclavian artery, causes hand and forearm pain and weakness from ischemia
What is the cause of, and what are the symptoms of venous thoracic outlet syndrome?
subclavian vein thrombosis. arm cyanosis and swelling
What are common causes of upper trunk lesions? (2)
forceful shoulder compression, birth trauma
What are risk factors for upper brachial plexus injury at birth? name 4
maternal obesity, multiparity, large baby size >> obstetrical intervention
What is more common, supraclavicular or infraclavicular brachial plexus lesion? And which parts of the brachial plexus are affected in each?
Supraclavicular are more common
upper trunk (C5-6)
middle trunk (C7)
lower trunk (C8-T1)
Draw the brachial plexus! :)
What are the symptoms of an upper trunk lesion? What is the eponym and the common name for the weakness pattern in the arm? What about muscles around the shoulder? And sensory deficits?
- shoulder abduction (supraspinatus and deltoid)
- external rotation (infraspinatus)
- elbow flexion (biceps, brachioradialis)
- forearm supination
-> internally rotated and adducted arm
=> Duchenne-Erb palsy or waiter's tip
- scapula elevation (rhomboid, levator scapulae - dorsal scapular nerve, C5)
- scapula winging (serratus anterior - long thorarcic nerve, C5-7)
- sensory: lateral arm, lateral forearm, lateral hand and fingers
What are the symptoms of a middle trunk injury?
rarely in isolation
- elbow extension
- wrist extension
- finger extension
- forearm pronation (pronator teres and quadratus)
-> decorticate-like posture
- sensory: posterior forearm and dorsal and palmar middle finger
picutre decorticate, decerebrate
What are the symptoms of a lower trunk injury? What causes it (3)? What's the eponym
traumatic extension (catching oneself while falling), breech delivery, apical lung tumors such are Pancoast tumors
- wrist flexion
- finger flexion
- all hand intrinsic muscles
-> claw-like posture
= Klumpke's pasy
- sensory loss: medial forearm and hand
When can you see a Horner's with a lower plexus injury?
when the T1 motor root is injured prior to its fusion into the lower trunk, that is, before the preganglionic sympathetic fibers exit the nerve root and enter the cervical sympathetic chain
What is a Horner's syndrome?
ipsilateral ptosis, miosis, anhidrosis in the face and neck, also problems with accomodation
picture Klumpke's palsy
picture Duchenne-Erb's palsy
What happens in a lateral cord injury?
- shoulder flexion
- shoulder abduction
- elbow flexion
- elbow pronation
- wrist flexion towrads the radial side
sensory loss of
- upper arm
- lateral forearm
- lateral and palmar hand and fingers
What happens in a medial cord injury? What is it similar to?
- wrist flexion to ulnar side
- finger flexion and extension
- hand intrinsic muscles
similar to Klumpke's except sparing of radial innervated finger extension musclse
- medial side of upper extremity
What happens in a posterior cord injury?
- shoulder abduction (deltoid)
- shoulder adduction (latissimus dorsi - thoracodorsal nerve, teres major - lower subscapular nerve)
- elbow extension
- forearm supination
- wrist extension
- finger extension
- shoulder area
- posterior upper and lower arm
- dorsum of the hand
Which roots form the lumbar plexus?
What are symptoms with lumbar versus sacral plexus lesions?
pain worsens with hip extension and straight leg raise (as w radics)
lumbar: pain in back, pelvis, or anterior thigh
sacral: posterior thigh, calf, foot
lumbar: hip flexion and knee extension
sacral: hip extension and ankle movements
pudendal nerve or S2-4: bowel and bladder dysfunction (rare)
Sensory: in nerve distribution
Name 6 causes of lumbosacral plexopathy
mass lesion: retroperitoneal hematoma, psoas abscess
trauma: fracture, obstetric injury, surgical positioning
How do you diagnose brachial and lumbar plexopathy?
XR for fractures
CT myelography and MRI for cord (CT myelo better than conventional myelo, esp C5-6 lesions)
MRI, radionucleotide for malignancy
MRI with contrast for inflammation, immune-mediated plexopathy and nerve sheath tumor
What does spontaneous activity or the absence thereof in paraspinal muscles indicate?
absence: doesn't mean nothing
presence: nerve root injury
How do you treat lumbosacral and cervical plexopathy? (4)
usually conservatively, with pain control
traumatic: anastomosis of transected neuroal elements, but this is usually ineffective for root injuries and lower trunk brachial plexus injuries
roids if immune-mediated
destruction of the dorsal root entry zone may help with pain
What does and what does not increase the risk of a focal nerve injury?
does not: one focal nerve injury does not increase susceptibility o second focal injury
Define Wallerian degeneration
disintegration of the nerve distal to site of injury
What are Bands of Bungner
endoneurial tubes formed by proliferated Schwann cells late in Wallerian degeneration, which form a substrate for neural regeneration
What are ovoids?
myelin breakdown into small compartments during Wallerian degeneration
What is the order of progression in Wallerian degeneration? (6)
begins 4-10 days after axon injury
1. accumulation of organelles and mitos, Schwann cell retraction and myelin breakdown in paranodal areas near injury
2. disinteration of smooth endoplasmatic reticulum in the neruonal soma
3. breakdown of microtubule and intermediate fiber structures
4. axon becomes fragmented and myelin breaks down into ovoids
5. Axon fragments are phagocytosed by macrophages (late response)
6. Schwann cells proliferate and form endoneurial tubers = Bands of Bungner within their basal lamina, which is a substrate for regeneration
1. sammeln und zusammenziehen, 2. production stirbt 3. transport system stirbt 4. highway stirbt 5. die Reste werden abtransportiert 6. es gibt doch Hoffnung
What causes Wallerian degeneration? (6)
1. compression, entrapment, trauma
2. vasculitis - isolated to peripheral nerve, a/w systemic vasculitis (polyarteritis nodosa, Wegener, Chrug-Strauss), a/w connective tissue d/o (lupus, RA)
3. immune-mediated (multifocal motor neuropathy, CIDP)
4. infxn (PPh: toxic effect of prganism vs vasculopathy in lyme, HIV vs activation of virus in cell body in HSV)
What 2 structures form the carpal tunnel?
transverse carpal ligament superiorly,
carpal bones inferiorly
What are risk factors for CTS?
repetitive hand use (50%), obesity, pregnancy, endocrinopathy (hypothyroidism, diabetes), rheumatoid or osteoarthritis, previous wrist fracture
What are symptoms of CTS? 3
paresthesias - only 50% localized to median distribution, often involves whole hand but should spare thenar eminence (median branch comes off before wrist), worse in sleep or w sustained hand positions
weakness of thumb abduction & opposition - abductor pollicis brevis and opponens pollicis, thenar atrophy (esp fast in elderly), weakness of flexor pollicis brevis (partly ulnar innervated) and 1st and 2nd lumbricals usually asxs
If there is median nerve injury, what does wrist flexor weakness tell you about localization?
injury is above the wrist
What tests to do for CTS? 2
serology for hypothyroidism, diabetes, pregancy
What is the treatement for CTS?
medical tx: attempt 4-6 weeks if mild - avoid repetitive motions, neutral wrist splint, NSAIDs, diuretics, local roids
surgical open or endoscopic: if atrophy, refractory
What are bad prognostic signs in CTS for conservative treatment? (2)
duration > 10 mo
What are localizations and etiologies of anterior interosseous syndrome?
locations: as it passes over the two heads of the pronator teres, or by muscles/tendon anomalies
etiologies: repetitive elbow flexion, local trauma (radius fracture, venipuncture)
The anterior interosseous is a branch of what?
What are the symptoms of anterior interosseous syndrome? name the 3 weaknesses
no sensory loss (pure motor branch)
- distal thumb flexion (flexor pollicis longus)
- 2nd/3rd digit flexion (radial side of flexor digitorum profundus)
- pronation (pronator quadratus)
for some reason, it mentions here that w Martin-Gruber anastomosis, intrinsic hand muscles may be weak
What are the diagnostic tests for anterior interosseous syndrome?
NCS not so helpful as nerve cannot be studied alone
EMG: sparing of wrist flexion differentiates anterior interosseous from more proximal median nerve injury (flexor carpi radialis, C6-7)
How do you treat the anterior interosseous syndrome? 4
avoid provocative movements, NSAIDs, local roids, surgical to explore if no obvious cause and if refractory to medical tx for 6 mo
Ulnar nerve compression at the elbow PPh
No soft-tissue protection at cubital tunnel
What is the other name for cubital tunnel?
humero-ulnar aponeurotic arcade
What is typical posture/sign for median neuropathy? Where is the lesion?
finger flexor weakness with
lesion proximal to the wrist
What can cause cubital tunnel syndromes? 5
bone deformities (old fracture, arthritis)
anatomical variations (accessory anconeous muscle, olecranon hypertrophy)
Where is the anconeous muscle?
posterior surface at lateral epicondyle
What are symptoms of ulnar neuropathy at the elbow?
exacerbated by flexion
paresthesias of digit 4 and 5 (20% also 3rd, 20% only 5th)
weakness of intrinsic hand muscles, wrist flexion (FCU), 4th and 5th digit flexion (FDP)
What is the weakness pattern in
- ulnar lesion
- lower brachial plexus lesion
- C8 lesion?
ulnar: digit $ and 5 sensory
- intrinsic hand muscles, FDI
lower brachial plexus: Th1 and C8 sensory dermatome
- flexor muscles of the forearm
- a little ABP weakness
C8 lesion: C8 dermatome
- radial nerve & triceps
- pronator teres, palmaris longus
- flexor muscles of the forearm
- APB, IO
How do you diagnose ulnar neuropathy at the elbow?
NCS: slowing of conduction velocity or conduction block across the elbow (the latter in 70% of cases with weakness on exam), reduced amplitude if severe
EMG: FDP (or FCU)
What is the treatment of ulnar neuropathy at the elbow?
2-3 months of splints, NSAIDs
roids have no benefit
- nerve transposition if injury at medial epicondyle of humerus
What is the PPh of ulnar neuropathy at the wrist? What is the name of the anatomical structure? And what are its borders?
- radial: hook of hamate (Hakenbein)
- roof: transverse carpal ligament
- ulnar: pisiform bone (Erbsenbein)
- floor: pisiohamate ligament
What causes ulnar neuropathy at the wrist?
trauma, extrenal compression (bkining), fracture, ganglion cyst, synovial cyst, tumor
What is the other name for ganglion cyst?
What symptoms does ulnar neuropathy at the wrist cause?
- Guyon's canal
- superficial sensory nerve only
- deep motor branch
- distal portion of deep motor branch
- sensory loss on volar aspect of 4th and 5th digit
- weakness of ulnar-innervated hand muscles
superficial sensory nerve
- sparing of motor
deep motor branch
- spares sensory, affects all hand muscles
distal portion of deep motor branch
- spares hypothenar muscles and sensory, affects FDI
How do you diagnose ulnar neuropathy at the wrist?
prolonged distal latency, evtl decr amplitude in ADM and FDI and sensory
EMG: muscles proximal to wrist (FDP, FCU) are nl
How do you treat ulnar neuropathy at the wrist?
splint, NSAIDs, surgical if trauma or refractory
What causes radial nerve injury (2)? What is the eponym (1)?
Saturday night palsy
proximal humeral fracture, or prolonged compression at the spiral groove
What are sxs of radial nerve compression? (3 muscles)
- wrist extensors
- finger extensors
- radial side of dorsal hand and thumb
- dorsal brachium and antebrachium
Dx of radial nerve injury
NCS: conduction block at spiral groove
EMG: evidence of denervation
Tx of radial nerve injury - how can you make a wrist extend again?
medical : splints to wrist support and to prevent contractures
surgical: after severe trauma or 4 mo of failed medical tx
tendon transfer from anterior forearm comppartment to wrist and thumb extensors allows for wrist extension
picture radial sensory distribution
The posterior interosseous nerve is a branch of what nerve? What's its course in the arm?
the radial nerve:
the radial nerve splits near the elbow into a pure sensory branch (ramus superficialis) and a pure motor branch (ramus profundus = posterior interosseous branch). The latter run through the radial tunnel (by regional bones and muscles) and the arcade of Frohse (formed by supinator muscle fascia)
picture the arcade of Frohse
What are the sxs in posterior interosseous syndrome?
- weakness of wrist and finger extension
- ECR (extensor carpi radialis) may be spared because branch comes off proximal to arcade of Frohse
- no sensory loss at it's a pure motor branch
Dx of posterior interosseous syndrome?
NCS: conduction block
Tx of posterior interosseous syndrome?
wrist extension splint, local glucocorticosteroids, surgical exploration
What is innervated by the ANTERIOR interosseous nerve? Where is it often injured (2)?
branch of the median nerve,
often injured at two heads of pronator teres, or repetitive elbow flexion/trauma
- weakness of distal thumb flexion (FPL)
- weakness of 2nd and 3rd digit flexion (FDP)
- weakness of pronation (pronator quadratus)
- no sensory loss - pure motor branch
Where does the femoral nerve get injured, and how?
- retroperitoneal or iiliacus hematoma
- surgical positioning (lithotomy)
- inguinal ligament compression after prolonged hip flexion or abduction w external rotation
- hip arthroplasty or dislocation
- penetrating groin trauma
What is weak, and where is the sensory loss in femoral nerve injuries?
- knee extension
- if above the inguinal ligament, hip flexion may also be weak
- sensory loss in the anterior thigh and medial calf due to saphenous nerve involvement
picture the anatomy of the femoral nerve
What diagnostic tests may be ordered for femoral neuropathy? Which muscles may you want to check on EMG? What are the treatment options?
CT of pelvis for retroperitoneal mass (abscess or hematoma)
NCS conduction block
EMG: denervation in femoral distribution. Sparing of hip adductors, hip abductor and extensors, and paraspinal muscles
Tx: Knee bracing, surgery if mass
What nerve supplies the hip adductors?
What nerve supplies the hip abductors and extensors?
What is the nerve that is injured in meralgia paresthetica?
lateral femoral cutaneous nerve
What causes meralgia paresthetica?
tight pants or belts, pannus
compression underneath inguinal ligament
What are the symptoms of meralgia paresthetica?
pain and sensory changes
What is the treatment for meralgia paresthetica?
weight loss, avoid compression
What causes peroneal lesions?
external compression (bedrest, surgical positioning, weight loss, prolonged leg crossing or squatting), structural pathology at the fibular head (cysts, tumors), fibular fracture or knee dislocation
What it the etiology of symptoms in the peroneal distribution that occur only when standing?
disruption of the tibio-fibular joint capsule causing synovial fluid dissection into the common peroneal nerve
What are symptoms of peroneal nerve injury? weakness (2), sensory (2)
- ankle eversion (superficial branch, peroneus longus)
- ankle dorsiflexion (deep peroneal branch, TA)
- anterior lateral lower leg and foot dorsum (superficial branch)
- 1st and 2nd digit web (deep peroneal branch)
Which nerve mediates ankle inversion and plantar flexion?
How do you diagnose peroneal nerve injuries?
NCS: conduction block. SNAP may be nl if only deep branch affected
- deep branch: TA
- superficial branch: peroneus longus, peroneus brevis
- short head of biceps femoris should be normal if lesion at fibula (common peroneal, L5-S1)
What nerve supplies the long head of the biceps femoris muscle?
tibial nerve, L5-S1
How is an L5 lesion different from a peroneal lesion? (4)
- weakness in hip abduction
- weakness in foot inversion
- numbness on the sole
- numbness above the knee
Picture the sensory distribution of the peroneal nerve
Picture the L5 dermatome