Peripheral Nerves Flashcards
Shoulder Abduction
Axillary Nerve
C5
Elbow Flexion weakness
Musculocutaneous
Elbow Extension weakness
Radial
Wrist extension weakness
Radial
Wrist flexion weakness
Median
Finger extension weakness
Radial
Finger flexion weakness
Median/(Ulnar)
Axillary Nerve
Deltoid muscle
Shoulder abduction 20-90deg
Regimental patch
C5
Critical movement: Elbow flexors
Controls shoulder
Other:
Half of biceps and brachioradialis jerk
Also shoulder abduction
C6
Elbow joint
Wrist extensors
Also
Elbow flexion with C5
Part of bicps an brachioradialis jerk
C7
Wrist joint
Elbow extension
Triceps Jerk
Also related to wrist extension/flexion
C8
Finger flexion/extension
Key movement is flexion
Part of triceps jerk
T1
Finger abductors
Also involved in finger adduction
Radial Nerve
Extension of everything
Elbow weakness if injury above spiral groove
Brachioradialis, wrist and finger weakness: injury in spiral groove
finger abduction appears weak because hard to spread fingers if not straight!
Sensation:
Posterior aspect of arm
Posterior aspect of hand
Snuffbox
Location of lesion
Brachioradialis reflex
What does it mean in the upper limb if extension and flexion are weak at the same joint?
Can’t be a peripheral nerve lesion
Sensation of medial aspect of forearm
From brachial plexus
Winging of Scapula
Proximal lesion
Musculocutaneous Nerve
Motor: Elbow Flexion
Sensory: Lateral forearm
Sensation loss involving forearm and hand
Radiculopathy
Median Nerve
Wrist flexion
Finger flexion
Lumbricals
Thumb Abduction
LOAF of hand (thenar eminence): lateral 2 lumbricals, opponens pollicis brevis, abductor pollicis brevis, flexor pollicis brevis
Weakness: wrist and finger flexion
Hand of benediction → unable to flex middle and index finger
Sensation: lateral 3.5 digits
Plus don’t forget palmar branch
Ulnar Nerve
Finger abduction
Finger adduction
For digit 4 + 5: Flexor digitorum profundus and lumbricals
Wasting of intrinsic muscles of hand except thenar
Weak finger abduction and adduction
Ulnar claw hand: hyperextension of MCPJ, flexion at PIPJ and DIPJ
(Higher the lesion, less the deformity - because FDP also weak and doesn’t try to overcome lumbrical weakness)
Froment’s sign: Adductor pollicis weakness, flexor pollicis longus activats instead
Sensory medial aspect 1.5 fingers
Biceps Jerk
C5/C6
Musculocutaneous
Brachioradialis Jerk
C5/C6
Radial
Triceps Jerk
C7/C8
Radial
Upper Trunk Brachial Plexus injury
Loss of C5 and C6
Loss of shoulder movement
Loss of elbow flexion
“waiter’s tip position”
Sensory: lateral aspect of arm and forearm (musculocutaneous)
Lower Trunk Brachial Plexus Injury
C8 - T1
Loss of everything in the hand
Loss of sensation along medial aspect of hand and forearm
Can get a Horner’s syndrome because the sympathetic pathways come from C8-T1 too.
Femoral Nerve
Hip Flexion
Knee Extension (Quads)
Sensation: medial aspect of thigh
Loss of knee jerk
Sciatic Nerve
Knee flexion
Plus distal movement
Flaccid foot drop
Loss of sensation below knee
Loss of ankle jerk and plantar response
Tibial Nerve
Posterior compartment
Plantarflexion
Ankle Inversion
Loss of ankle jerk
Sensory: most of sole of foot
Common Peroneal Nerve
Ankle eversion (Superficial peroneal)
Dorsiflexion - foot drop (Deep peroneal)
Sensory:
Superficial: lateral aspect leg, dorsum of foot
Deep: between 1st and 2nd toe
Inferior Gluteal Nerve
Gluteus Maximus - Hip extension
Obturator Nerve
Hip Adductors
L2
Hip Flexors
L3
Knee Extensors
L4
Ankle Dorsiflexion
Inversion
L5
Long toe extensors
Inversion/eversion
S1
Ankle plantar flexion
Eversion
Myotomes for lower limb
Count down joints
Then around joints
L3 versus Femoral lesion
L3 has addition to hip adduction weakness
Otherwise:
Knee extension weakness
Hip flexion weakness
Loss of Knee Jerk
Sensation similar - down onto knee
Knee Jerk
Femoral Nerve
L3 L4
Ankle Jerk
Tibial Nerve
S1 S2
Foot Drop
L4/L5: loss of inversion/eversion, but jerk present
Sciatic: everything gone
Common peroneal: eversion gone, but jerk and inversion present (because tibial does this)
Unmyelinated nerves
Small fibre nerves
Pain and autonomic signals
What does Nerve Conduction Studies test?
Large Myelinated fibres record best
Aids localisation
Can’t test small fibres or autonomic fibres
Motor: anterior horn cell to muscle (Includes NMJ)
Sensory: skin to dorsal root ganglia
NCS in sensory radiculopathy
Normal
Amplitude loss on NCS
Axonal loss
Conduction Velocity slowing on NCS
Demyelination
Initial finding in compression is sensory CV slowing
Temporal dispersion on NCS
Marker of demyelination
F wave on NCS
Signal goes wrong way up to anterior horn then bounces back, so can assess proximal segment of nerve
May be the only abnormality in early GBS
Inflammatory Peripheral Neuropathy
Onset is subacute
Proximal and Distal: AIDP, CIDP
Asymmetric: Multifocal motor neuropathy, Mononeuritis multiplex
Constitutional symptoms
Leprosy
Mycobacterium leprae
Consider: low/middle income countries with skin lesions, cutaneous sensory loss, thick nerves on palpation, focal mononeuropathies
Sparing of reflexes and dorsal columns
Responsive to antibiotics
Focal, asymmetric axonal loss
Mononeuritis Multiplex
Bilateral CN VII Palsy
Most commonly affected nerve in sarcoidosis
Parotid swelling can also cause this, part of Heerfordt Syndrome with uveitis, transverse myelitis
Sarcoidosis
Small fibre neuropathy is most common presentation for nerve involvement
Bilateral CN VII is the key nerve involvement
Hereditary Neuropathy with Liability to Pressure Palsy (HNPP)
Deletion of ch 17p11.2 containing PMP22 gene
AD inheritance
Predisposition to getting compressive neuropathies
HIV Neuropathy
Distal, symmetric, sensory neuropathy affecting small sensory fibres or both
Posirtive and negative symptoms, most have pain
Usually no motor symptoms
Isoniazid exposure, advanced age increase risk
Paraneoplastic Peripheral Neuropathy
Sensory, motor and small fibre
Axonal or demyelinating
Anti Hu, Anti CV2
Charcot Marie Tooth Neuropathy
Genetic condition with peripheral neuropathy main manifestation.
Insidious onset, can develop during infancy, can develop foot deformities.
Lack of positive sensory symptoms despite clear sensory involvement.
Loss of reflexes
Loss of fine motor movement in hands is a late finding
AD inheritance Demyelinating (CMT1): motor predominant
AD inheritance Axonal (CMT2): sensory predominant
Also X linked and AR forms
Diabetic Neuropathy
Broad spectrum of involvement, including small fibres and autonomic fibres. Even cranial nerves.
Distal symmetric sensorimotor peripheral neuropathy, sensory predominant. Positive and negative symptoms.
Positive and negative symptoms, including pain. Weakness unusual early.
Diabetic Autonomic Neuropathy
Impacts morbidity and mortality
T1DM > T2DM
Increases with time
Resting tachycardia, exercise intolerance, postural hypotension, gastroparesis, dry skin
Best agent for painful peripheral neuropathy
Amitriptyline has lowest NNT
Duloxetine, venlafaxine, gabapentin and pregabalin are other options.
Drug related Peripheral Neuropathies
Key Chemotherapy agents causing Peripheral Neuropathy
Aensorimotor axonal length dependent neuropathy in majority
Platinum based (platins): develop very quickly, within weeks. Due to binding to DNA inducing apoptosis.
Taxanes (Paclitaxel, docetaxel) and Vinca alkaloids (Vincristine, vinblastine). Due to disruption of microtubules.
Bortezomib (Proteasome inhibitor) That is frequently dose limiting
Nutritional Causes of Peripheral Neuropathy
Vitamin B1
Vitamin B6
Vitamin B12 (subacute combined degeneration of dorsal column and spinocerebellar - UMN + proprioceptive loss)
Vitamin E
Copper
Thiamine deficiency
Which nerve is involved when there is Nerve Compression (Radiculopathy) in the Lumbar Spine?
Disc Herniation: lower of the two involved Vertebrae = involved nerve
Foraminal stenosis: upper of the two involved vertebrae = involved nerve
Radiculopathy Investigations
Sensory studies normal
Motor studies: normal or reduced amplitude
EMG: neurogenic changes in affected myotome muscle groups (increased amplitude, polyphasia, decreased recruitment)
Sciatica Management
Remain active
Don’t give opioids or pregabalin
Steroids variable
Physiotherapy
33% resolve within 2 weeks, 90% in 3 months spontaneously
Surgery may be helpful if pain persists past 4 months, unclear if improves weakness
Pathogenesis of Guillain-Barré Syndrome
AIDP
Mean age of onset 40, M > F
Humorally mediated disorder leading to TT lymphocyte infiltration and intense macrophage associated segmental demyelination in proximal nerve segments and nerve roots
Antibodies
Axonal subtype: GM1 GD1a
Miller Fisher: GQ1b
IgG and complement deposition
Molecular mimicry with campylobacter jejuni can play a role
Weakness predominant ascending pattern is most common but lots of others
Miller Fisher Syndrome features
Viral prodrome 1-2 weeks prior
Ophthalmoplegia
Loss of reflexes
Ataxia
GQ1b antibodies
Triggers for GBS
Prodromal illness in 4 weeks prior in 60-70% of cases
URTI and campylobacter jejuni most common
Surgery, malignancy (esp. Hodgkin Lymphoma), pregnancy, mycoplasma pneumoniae, CMV, EBV, HIV, VZV, HBV/HCV, Zika
Post immune checkpoint inhibitors
Classic CSF finding in GBS
Albuminocytologic dissociation
So markedly raised protein in CSF with normal or slightly raised white cell count
May be delayed if taken early
NCS in GBS
Prolonged F wave latency
Prolonged distal latencies/reduced velocity (motor before sensory)
Conduction block
Sural often preserved
Sensitivity is poor early in disease
Management of GBS
PLEx or IVIg
PLEx:
- Removes autoantibodies, immune complexes, cytokines
- Needs to be given within 2-4 weeks
- Reduces time to walk unaided by 32-41 days and time on ventilator by 2 weeks
IVIg:
- Benefit seen within 2 weeks in those unable to walk unaided
- Repeat dosing at 4 weeks if slow improvement is not necessarily helpful
No benefit of both
Oral Steroids → worse outcome
Infections with bad prognosis in GBS
Campylobacter jejuni
CMV
CIDP
Chronic version of AIDP, nadir past 4 weeks, usually progressive >8 weeks.
Lower limb predominant, but similar pattern of proximal and distal weakness. Usually milder than AIDP
NCS and LP findings similar
Treat with steroids
- Pulse MP 3 days, then monthly 1 day ongoing
- Long term IVIg often required
Nodopathy
Antibodies to the nodes and paranodal proteins.
Atypical disease
Specific antibodies
Rituximab for management
Checkpoint Inhibitor Induced Neuropathy
Can present like AIDP, also as a cranial neuropathy
Mechanism not fully understood
CSF pleocytosis typical compared to AIDP/CIDP
Treat with steroids
IgM Paraprotein Neuropathy
Older men
Sensory ataxia, mild weakness
Prolonged distal latency on NCS
50% have anti-MAG antibody
Rituximab
Can mimic CIDP - all with CIDP like presentation need paraproteins sent
Amyloid Peripheral Neuropathy
Painful length dependent small fibre peripheral neuropathy with generalised autonomic failure
Orthostatic hypotension common
for ATTR, can use Inotersen (antisense oligonucleotide) and Patisiran (RNA interference agent)
Multifocal Motor Neuropathy
Motor only components of peripheral nerves → asymmetric
Upper limb predominant
Decreased tendon reflexes in affected areas
Investigations:
- Serum anti-GM1 antibodies
- Motor conduction block
IVIg for management
steroids can worsen
Pure sensory loss of upper limbs at same time as or before lower limbs
Think about dorsal root ganglionopathy
HSV-2 Lumbosacral Radiculopathy
Radicular pain, paraesthesia, genital discomfort, lower extremity weakness.
If conus or caua equina involved, urinary retention can occur.
MRI: nerve root enlargement, T2 hyperintensity
CSF: lymphocytic pleocytosis, high protein
Aciclovir IV if immunocompromised
Otherwise Valacyclovir
Parsonage-Turner Syndrome
Severe pain in shoulder
Vasculitis of brachial plexus
Followed by weakness and atrophy of muscles of shoulder
Mostly middle aged men
Axonal loss as vessels infarct
Recover well with steroids
Lumbosacral Radiculoplexopathy
New name for diabetic amyotrophy
NMJ Dysfunction
- Weakness with no sensory symptoms
- Fatiguability
- Proximal symmetric weakness
- Respiratory symptoms
- Neck weakness
Motor Unit
1 motor nerve fibre and all the muscle fibres it innervates
Number of muscle fibres innervated by a single motor nerve fibre varies.
Spontaneous Activity
Abnormal
Denervated fibres express ACh receptors along their entire length, which leads to spontaneous firing due to background levels of ACh
Sign of active denervation
Fibrillation and positive spark waves
Fibrillation potentials and positive sharp waves
Abnormal spontaneous firing of individual muscle fibres, sign of active denervation and inflammatory myopathies
Fasciculations
Firing of part or all of a motor unit
Can be normal (Classic group is doctors and medical students)
Mostly abnormal however and occur when there are sick or dying axons
- MND
- CIDP
- Chronic nerve entrapments
Neurogenic Morphology on EMG
- Broad and polyphasic morphology as there muscle axons are messy
- Also increased amplitude because more muscles fibres firing from the same muscle axon
- Reduced recruitment with maximum contraction as fewer motor units
Myopathic Morphology
Smaller amplitude as fewer fibres in each motor unit so smaller signal
Increased or early recruitment as need lots of motor units for same force
Presynaptic NMJ Dysfunction
- Lambert Eaton Myasthenic Syndrome (Voltage gated calcium channel disorder)
- Botulism (vesicle problem)
Postsynaptic NMJ Dysfunction
Myasthenia Gravis (Ab against ACh receptors)
Organophosphate poisoning (Acetylcholinesterase problem)
Most common presentation of Myasthenia
Ocular symptoms: Ptosis, diplopia
Can mimic just about anything
Generalised weakness, fluctuating and fatiguable
Bulbar weakness, neck weakness, limb girdle, respiratory weakness.
Check accomodation
Myasthenia Gravis Diagnosis
- Ice test
- Check for antibodies: AChR (85%), MuSK (6-10%)
- Single nerve fibre (good for ocular) and repetitive nerve stimulation (10% decrement diagnostic - good for general)
- Tensilon test (Edrophonium administration)
- Hold eyes up, double vision occurs
Ocular Myasthenia
15% of patients have isolated ocular myasthenia (although often the presenting symptom of generalised)
50% AChR Ab positive
66% will progress to generalised within 2 years
90% who don’t generalise within 2 years remain ocular
MuSK Disease
IgG4 disease, non complement activating. Receptors not destroyed and thus respond quite well to Rituximab
Early onset, severe disease. Not related to thymoma
Management of Myasthenia Gravis
Remove Thymoma if present (unless MuSK Ab)
Cholinesterase inhibitors: Pyridostigmine
Steroids: reduce risk of developing generalised MG, however can worsen before improving if give too much
AZA, MMF, Tac, MTX
IVIg, PLEx as rescue therapy
Evidence for Rituximab as a single dose for new onset AChR+ve disease
Complement Inhibition and Myasthenia Gravis
Eculizumab, Ravulizumab, zilucoplan
Used for generalised AChR+ moderate severity disease who’ve already had some form of immunosuppression which they’ve failed.
Need meningococcal vaccine prior
Works rapidly
Neonatal Fc Receptor Myasthenia Gravis
Neonatal Fc Receptor molecule recycles IgG, extending half life. Keeps IgG around, and thus maintains availability of IgGZ autoantibodies in IgG mediated disease
Efgartimod and Rozanolixizumab are human IgG1 Ab Fc-fragment, with higher affinity to the FcRn → outcompetes endogenous IgG → Pathogenic IgG degraded
Improves outcomes.
IVIg is essentially a blunt tool to overwhelm FcRn. More expensive.
Benefits of Thymectomy in MG
Thymoma should be removed. Thymic hyperplasia should be removed if ACHr+ generalised disease.
Lower disease scores
Lower pred requirement
Fewer patients on AZA
Fewer admissions
Fewer immunosuppression side effects
Myasthenic Crisis
Severe respiratory weakness due to fatigue
Treatment
- Intubate
- IVIg
- PLEx
- Supportive Care
- Immunosuppression
5% mortality
Medications that can trigger Myasthenic Crisis
Aminoglycosides
Fluoroquinolones
Tetracyclines
Macrolides
Beta blockers
CCB (Verapamil)
Phenytoin
Lithium
HLA-B8-DR3
NOn paraneoplastic Lambert Eaton
Triad of:
- Proximal weakness that temporarily improves post exercise
- Autonomic Features: dry mouth, urinary retention, orthostatic hypotension
- Areflexia: post exercise facilitation
Lambert Eaton Myasthenic Syndrome
Lambert Eaton Diagnosis
NCS: Attentuated CMAP without muscle mass loss, increases post exercise
EMG: abnormal
VGCC Ab positive in 90-100% of patients
Malignancy screen
Lambert Eaton Treatment
- Tumour resection if present
- 3-4-diaminopyridine: blocks efflux of potassium ions, prolonging depolarisation (as disease is due to problems with calcium channels)
- Immunosuppression, IVIg
Mechanism of Botulinium Toxin
Blocks presynaptic Acetylcholine release
Foodborne Botulism
2 day incubation
Starts in eyes and descends
Symmetric descending flaccid paralysis
Autonomic symptoms
Internal and external ophthalmoplegia (fixed pupils)
Reflexes and cognition preserved
Management of Botulism
- Avoid aminoglycosides
- Remove unabsorbed toxin if appropriate, e.g. ileus
- Equine trivalent (A, B, E) antitoxin: lowers mortality, shortens course of illness. Stabilises but doesn’t reverse disease
Recover over months, but some symptoms can persist for years.
