Myopathy, NMJ, peripheral nerve, anterior horn Flashcards
Brachial neuritis
a) Presentation vs cervical radiculopathy
b) Investigations
c) Management
a) - Severe acute pain in the shoulder/upper arm initially, not affected by movement (cervical radiculopathy is affected by movement), may keep them awake at night.
- The pain lasts 2-3 days
- ~1 week later - weakness/wasting in affected arm, affecting approx 2 nerves of brachial plexus (cervical radiculopathy tends to occur at same time as the pain)
- May be triggered by vaccination, infection, surgery, trauma
b) - MRI spine to r/o other cause
- 3 weeks post-onset, perform NCS (earlier than this may show false negative)
c) - Pain management
- Once pain improved, physiotherapy
- Improves without treatment after a few months
Myotomes
a) Upper limbs C4-T1
b) Lower limbs L2-S1
C4 - shoulder shrug
C5 - shoulder abduction, elbow flexion
C6 - wrist extension
C7 - elbow extension
C8 - finger flexion, thumb abduction
T1 - finger abduction
L2 - hip flexion
L3 - knee extension
L4 - foot dorsiflexion
L5 - hallux dorsiflexion
S1 - foot plantarflexion
Dermatomes
a) Upper limb
b) Trunk
c) Lower limb
Upper limb:
C4: over the acromioclavicular joint
C5: “regimental badge”
C6: the palmar side of the thumb
C7: the palmar side of the middle finger
C8: the palmar side of the little finger
T1: medial aspect ACF
Trunk:
- T4: nipple
- T6: xiphoid process
- T10: umbilicus
Lower limb:
L1: the inguinal region and the very top of the medial thigh.
L2: the middle and lateral aspect of the anterior thigh.
L3: the medial epicondyle of the femur.
L4: the medial malleolus.
L5: the dorsum of the foot at the third metatarsophalangeal joint.
S1: the lateral aspect of the calcaneus.
S2: at the midpoint of the popliteal fossa.
S3: at the horizontal gluteal crease (the horizontal crease formed by the inferior aspect of the buttocks and the posterior upper thigh).
S4/5: the perianal area.
Innervation of lower limb
a) Describe the nerve roots and movements for each of the main nerves in the lower limb
b) Explain the presentation of each palsy
c) Peroneal nerve palsy vs. L5 radiculopathy
d) Which disc protrusion causes (i) L5 radiculopathy, (ii) C7 radiculopathy
e) Assessment of footdrop
f) What is meralgia paraesthetica? How is it differentiated from other pathology?
Common peroneal nerve:
- Peroneal Eversion Dorsiflexion (PED)
- Compression at fibular head/trauma, mononeuritis, MND
- Damage causes weakness in eversion and dorsiflexion (preserved inversion and plantarflexion)
- Also have reduced sensation in lateral aspect of leg
Tibial nerve:
- Tibial Inversion Plantarflexion (TIP)
(not a cause of footdrop)
- May be caused by tarsal tunnel syndrome (pain, numbness affecting first 3 1/2 toes), e.g. by fallen arches
Sciatic nerve:
- L5-S2
- LED + TIP (all movements at foot)
- Plus… knee flexion
L5 radiculopathy: (LIED)
- L5 Inversion Eversion Dorsiflexion
- Plus… hip abduction
- Lateral hip pain common, pain on SLR/dorsiflexion
- Lumbar disc disease, sciatica
Obturator nerve:
- Hip adduction
- Medial sensation of thigh
Femoral nerve:
- L2-L4
- Damage causes weakness of hip flexion (iliopsoas, L2 root) and knee extension (quads, L3 root), with sensory loss in anterior thigh and medial leg
- Will also cause loss of antero-medial sensation to the leg and hallux (saphenous nerve)
- May be caused by retroperitoneal haematoma (beware patients on anticoagulation)
d) - Cervical spinal nerves (C1-8) arise ABOVE the corresponding cervical vertebral bones (C8 arises above T1). Therefore, C7 radiculopathy will be caused by a C6/7 disc protrusion (as C7 arises above C7 vertebra - i.e. between C6 and C7)
- Thoracic and lumbar spinal nerves arise BELOW corresponding vertebral bones. Therefore, L5 radiculopathy will be caused by an L5/S1 disc protrusion (as L5 root arises below L5 vertebra - i.e. between L5 and S1)
e) Footdrop:
- Causes: peroneal neuropathy (habitual leg crossing, fibular neck compression, “slimmer’s palsy”, MND, mononeuritis, diabetes, alcohol, B12), L5 radiculopathy (back pain), sciatic neuropathy (hip surgery), lumbar plexopathy, compartment syndrome (painful!)
- Assess normal gait (slap/drag) and heel walking
- Assess foot movements (dorsi/plantar/inversion/eversion) and knee/hip (hip abduction weak - L5; knee flexion weak - sciatic)
- Assess sensation - midfoot (L5 dermatome), lateral leg (common peroneal)
- Assess for back pain. Assess for fibular compression. Assess for Baker’s cysts
- Tinels sign - tap at fibular head - if causes symptoms likely fibular compression cause
- Assess for other neurology ?fasiculations/ atrophy/ reflexes/ plantars - ?ALS etc.
f) - Compression of lateral femoral cutaneous nerve (L2-L3) around the inguinal ligament/ASIS
- Risk factors - bending down, cycling, pregnancy, obesity, pressure or trauma in that area (e.g. tight low-waisted trousers)
- Presents with purely sensory symptoms - pain, paraesthesia and numbness in the anterolateral thigh, often worse with walking/bending down
- vs L2-L3 nerve/root compression - does NOT cause weakness (normal hip flexion) and no back pain; pain/symptoms reproduced by pressing medial to ASIS or extension of hip (but have NORMAL straight leg raise)
- Should also exclude retroperitoneal mass (e.g. tumour, haemorrhage) and diabetic amyotrophy (tends to be symmetrical)
- NCS may be useful
- Management - weight loss, avoid compression, NSAIDs, neuropathic agents, steroid injections, surgery
Internuclear ophthalmoplegia and one-and-a-half syndrome
INO:
- Caused by damage to the MLF* (causes include MS - often bilateral, stroke - usually unilateral)
- Ipsilateral weakness in ADduction
- Contralateral horizontal nystagmus on ABduction
- No issue with ABduction on ipsilateral side or ADduction on contralateral side
- Lesion in the medial longitudinal fasciculus (connection between CN 3 and 6)
*MLF in the medial medulla - abnormalities could be part of a medial medullary syndrome
OAHS*:
- Caused by pontine lesions affecting the paramedian pontine reticular formation and MLF (causes include pontine stroke, tumour, MS)
- Ipsilateral horizontal gaze palsy
- Contralateral weakness in ADduction, often with nystagmus on ABduction
(could also be caused by CN VI palsy on ipsilateral side and MLF damage on contralateral side)
*One eye cannot move at all, the other can move halfway (i.e. one and a half syndrome)
Demyelinating polyneuropathies
- AIDP (GBS) - typical presentation, results and management
- vs Miller-Fisher - triad, antibodies, etc.
- vs BBE
- vs CIDP
- vs MMN
- features on NCS
GBS:
- Causes include 75% preceding GI/resp infection, lymphoma, vaccines
- Clinical fx: ascending symmetrical weakness, areflexia, sensory loss, may involve bulbar/respiratory muscles, autonomic dysreflexia. Note that back pain is a common feature so don’t assume this means CES
- Peak symptoms at 4 weeks
- Monitor FVC, ECG
- CSF - albuminocytological dissociation (elevated protein with normal WCC)
- Anti-GM1 antibodies may be present (esp. recent c.jejuni infection)
- NCS: segmental demyelination with conduction block and temporal dispertion (in severe cases may cause axonal degeneration, with action potential amplitude reduction)
- Rx: supportive, IVIG, plasma exchange
Miller-Fisher:
- Similar to GBS, acute progression over days, often 1-4 weeks following infection, e.g. gastroenteritis
- Classic triad: ataxia, ophthalmoplegia, areflexia
- Affects cranial/facial nerves (e.g. opthlalmoplegia, ptosis, facial palsy, dysphagia, dysarthria) but not limb weakness
- CSF elevated protein, antibodies to ganglioside GQ1b (90%)
- May progress to involve limbs/respiratory (evolving into GBS)
BBE:
- Brachial-cervical-pharyngeal weakness with ophthalmoplegia, ataxia and encephalopathy (Miller fisher with confusion or coma)
- May have hyperreflexia and upgoing plantars
- also associated with GQ1b antibody
CIDP:
- Symptoms lasting >8 weeks, slowly progressing
- Typical - symmetrical distal and proximal weakness, areflexia
- Atypical - multifocal (asymmetric)
MMN:
- Pure motor neuropathy (LMN pattern of weakness)
- Asymmetrical, predominantly affecting upper limbs, does not affect bulbar muscles, often following a particular peripheral nerve
- Weakness may be worse in the cold
- Conduction blocks on NCS
- Anti-GM1 antibodies
- Rx: IVIG
Nerve conduction studies
- Axonal vs demyelinating neuropathy
- Examples of each
- Which does isoniazid cause? How can this risk be reduced?
Axonal
- action potential amplitude reduced, conduction speed preserved
- Amplitude of compound muscle action potential (CMAP) correlates with the number of motor nerve axons, and amplitude of sensory nerve action potential (SNAP) reflects the number of sensory nerve axons.
- There may also be evidence of active denervation in EMG - neurogenic pattern (few motor units but some with very high activity - positive sharp waves and fibrillations)
- Alcoholic neuropathy is pure axonal; paraneoplastic is usually axonal; diabetic is mixed axonal and demyelinating.
- MND causes retrograde axonal neuropathy, and should not have features of demyelination or conduction block
- Isoniazid causes axonal neuropathy, often painful, which can be reduced by use of pyridoxine (vitamin B6)
Demyelinating
- conduction speed reduced, action potentials normal.
Note that in severe demyelinating disease, axonal loss may follow.
- GBS/CIDP demyelinating; compressive neuropathy demyelinating
- Note that severe cases of demyelinating neuropathy may progress to involve the axons
Patterns of neuropathy:
a) Symmetric, length-dependent distal weakness with sensory loss (Most Common type)
b) Symmetric proximal and distal weakness with sensory loss and areflexia
c) Multiple mononeuropathies
d) Asymmetric weakness with intact sensory exam
e) Asymmetric weakness with pain in a dermatomal distribution
f) Sensory ataxia with or without weakness
g) Significant autonomic involvement
a) Metabolic neuropathies (e.g. diabetes), toxic neuropathies, Charcot-Marie-Tooth disease
b) Inflammatory demyelinating polyneuropathies (CIDP and GBS)
c) Vasculitic neuropathy (mononeuritis multiplex), hereditary neuropathy with liability to pressure palsies (HNPP)
d) Motor neuron disease, multifocal motor neuropathy, atypical CIDP
e) Radiculopathy
f) Sensory neuronopathies from paraneoplastic syndrome, Sjogren’s syndrome, DM, etc.
g) Amyloidosis, diabetic neuropathy, Sjogren’s, Parkinson’s-Plus syndromes
Trendelenburg sign
- what is it
- cause
- When standing on affected leg, pelvis will drop to contralateral side
- Damage to superior gluteal nerve (e.g. IM injection)
Demyelination
a) Wallerian vs. segmental demyelination
b) Findings on NCS
Wallerian demyelination involves demyelination distal to a focal lesion/trauma (e.g. nerve compression)
Segmental demyelination occurs from an inflammatory process (e.g. GBS)
b) Reduced conduction velocity
Prolonged F wave latency
Normal action potential amplitude (SNAP and CMAP)
Genetic cause of adrenal insufficiency + demyelination
a) Name
b) Inheritance and gene
c) Presentation
d) Tests
e) Treatment
a) X-linked adrenoleukodystrophy
b) X-linked
- ABCD1 gene
c) 3 types:
- Childhood form - age 4-8, seizures, mobility issues, learning disability
- Early adulthood form - age 20s, MS-like presentation (myelopathy) + Addisonian syndrome
- Addisonian-only form
d) Very long chain fatty acids (VLCFA)
e) Lorenzo oil can reduce serum levels of VLCFA
Only curative treatment is bone marrow transplant
MG vs LEMS
- Both commonly cause proximal muscle weakness and can affect the respiratory, bulbar and ocular muscles
- MG affects CNs more often, especially extra-ocular muscles (90% MG have ptosis or diplopia vs 20-25% in LEMS)
- Both may be paraneoplastic: MG may be associated with thymoma, while 60% LEMS is from SCLC (smoking history)
- Both cause fatigable weakness, but LEMS may be better in the evening while MG is always worse in the evening
- LEMS almost always (90%) have autonomic symptoms (e.g. dry mouth, postural hypotension, urinary/bowel/sexual dysfunction); autonomic symptoms less common in MG
- LEMS - hyporeflexic (reflexes may improve after exertion); MG reflexes normal
- Antibodies to post-synaptic ACh receptor or MuSK in MG; antibodies to pre-synaptic voltage gated calcium channels in LEMS
- MG is more steroid responsive; LEMS often only improves if underlying malignancy is treated (though you can trial 3,4-Diaminopyridine i.e. amifampridine)
Spinal shock vs neurogenic shock
Spinal shock
- Flaccid paralysis and areflexia that occurs in the acute phase of a traumatic or ischaemic spinal cord injury (last hours to days, before progressing to typical UMN spinal cord pattern of weakness)
Neurogenic shock
- Hypotension + bradycardia (or lack of appropriate tachycardia)
- Caused by spinal cord lesions above T6, affecting sympathetic tone
Anterior vs. medial vs. posterior cavernous sinus syndrome
Anterior - affects V1
Medial - affects V1 + V2
Posterior - affects V1 + V2 + V3
Orbital apex syndrome vs. cavernous sinus syndrome vs. superior orbital fissure syndrome
Orbital apex syndrome:
- involves the optic canal and superior orbital fissure
- involves the optic nerve, plus CN III, IV and VI
- commonly causes proptosis and chemosis, may also cause Horner’s
- is generally indolent in presentation (weeks - months)
- may be caused by tumour extension into orbital apex (e.g. NP tumour, Burkitt’s, schwannoma, metastates)
- may also be caused by inflammatory (sarcoid, vasculitis) or infective (invasive sinusitis or orbital cellulitis)
Cavernous sinus syndrome
- Does not affect optic nerve, but commonly affects CN III, IV, V1, V2, VI
- Main cause is CST, which can be septic (usually staph aureus) or aseptic. Other causes include tumour infiltration, trauma and infective infiltration
- Septic CST usually results from peri-orbital or sinus infection, but may be from sepsis or distant site (septic emboli)
- Aseptic CST occurs in a pro-thrombotic state - genetic (e.g. antithrombin 3 def/protein C or S def/factor V leiden) or acquired (pregnancy, COCP, APLS, nephrotic syndrome, leukaemia, PRV)
- Presents with retro-orbital headache, proptosis, chemosis, ophthalmoplegia, fever (if septic CST), Horner’s, stroke-like syndrome, features of raised ICP
- Does NOT involve optic nerve, unless progressing into the orbital apex
- CN VI (lateral gaze) palsy often first due to position within sinus (surrounded by blood)
- Diagnose via cerebral MR venography
- Rx: fluids, LMWH
Superior orbital fissure syndrome:
- Main cause is trauma
- Features include the above (ophthalmoplegia, chemosis, proptosis), but…
- Does NOT affect optic nerve (vs. orbital apex syndrome)
- Does NOT cause Horner’s, unlikely to be painful, and unlikely to have features of raised ICP/sepsis (vs. CST)