Systemic nerve and muscle disease Flashcards
Peripheral Polyneuropaties - how to characterize
- acute or gradual onset (e.g. GBS/AIDP v DM PN)
- demyelinating or primarily axonal (e.g., decreased CV, increased latency, +/- CB; or decreased amplitude); or both
- sensor, motor, or both
- diffuse and symmetric or mutlifocal and asymmetric
most are symmetric and symptomatically/electrodiagnostically worse distally
DM PN - pathophysiology, Px, PE
most common form of PN
Hx elevated A1C and poor blood glucose control → narrowing ov vasa nevorum → length-dependent dying back of PNs (axonal loss)
Px: gradual onset numbness/tingling w burning pain in stocking and glove distribution
PE: claw toes and hand muscle atrophy, areflexic achilles reflexes
DM PN - NCS/EMG
primarily axonal (dying back of n) → decreased amplitude
NCS: decreased amplitude on SNAP/CMAPs; may have prolonged latency if demyelinating component (CB, temporal dispersion)
EMG: if axonal process (dying back) → decreased recruitment distal > proximal; polyphasicity (reinnervation)
findings typically symmetric
evaluate at least 3 limbs
GBS/AIDP - pathophysiology, Px, concerns, Tx
recent GI/respiratory infection → rapidly progressive motor polyneuropathy d/t immune system confusing myelin for foreign protein → acute onset ascending paralysis (e.g., over days) with ascending areflexia
quick Dx → quick Tx (IVIG/plasmapheresis) → better prognosis; concern for respiratory compromise
GBS/AIDP - NCS
NCS: 1st change is absent or delayed F waves; H reflexes may also become abnormal early on
abnormal F and H waves → suggests proximal lesion e.g., polyradiculopathy
demyelinating process
SNAP: prolonged latency, reduced amplitude w sural sparing (sural n. large w more myelin than median/ulnar)
CMAP: prolonged latency, decreased CV, +/- CB w abnormal temporal dispersion; usually amplitude is normal
GBS/AIDP - key prognostic factor on NCS
if distal CMAP amplitude is <20% upper limit of normal → bad prognosis
demyelination so severe that axonal loss is ocurring
GBS/AIDP - EMG
mainly demyelinating process → normal EMG if no axonal loss has taken place
if severe w lots of CB → decreased recruitment
several weeks after onset → may see fibs/sharps (active denervation) d/t secondary axonal loss
CIDP v AIDP
CIDP essentially relapsing-remitting AIDP
Px and EDS findings similar except symptom progression is much slower (months)
Tx: plasmapheresis, IVIG, steroids (unlike AIDP)
critical illness neuropathy EDX
axonal sensorimotor polyneuropathy following critical illness, Tx rehab
NCS: abnormal SNAPs and CMAPs (low amplitude d/t axonal loss)
EMG: LDLA (long duration, large amplitude), decreased recruitment (machine gun), fibs/sharps
few axons → fewer motor units doing all the work for muscle contraction
CMT etiology px
many subtypes; duplication of PMP 22 gene
gradual distal > proximal weakness, fewer sensory abnormalities
b/l foot drop, Champagne bottle legs d/t calf and anterior compartment muscle wasting → weak dorsiflexion
deletion of PMP 22 gene
gives HNPP - hereditary neuropathy with liability to pressure palsy
CMT 2
gives you axonal polyneuropathy → EDX: decreased amplitude SNAPs/CMAPs; active denervation/reinnervation on EMG
CMT 1
demyelinating → EDX prolonged latency, decreased CV, without conduction block or abnormal temporal dispersion
usually uniform demyelination w CMT
AIDP v CMT 1 EDX
CMT 1 demyelinating - uniformly therefore universally prolonged latency and decreased CV (without conduction block or abnormal temporal dispersion)
v AIDP - focal demyelination → conduction block at normally non entrapment sites
HIV neuropathy
polyneuropathy
typically distal axonal
symmetric
sensory > motor
NCS: abnormal amplitudes of SNAPs/CMAPs
EMG: abnormal spontaneous activity in distal > proximal muscles
Mononeuritis Multiplex
“mononeuritis multiplexonal” → axonal proccess
axonal peripheral n. injury (e.g., median neuropathy)
combined w other single peripheral n. injuries
Px: acutely, asymmetrically; weakness, numbness/tingling
usually d/t underlying vasculitis which damages axons (e.g., Diabetes, Wegener Granulomatosis, polyarteritis nodosa, lupus)
NCS/EMG: abnormalities in respective peripheral nerves, axonal features generally
MG - EDX
NCS: normal routine studies
abnormal repetitive nerve stimulation
EMG: normal, perhaps increased jitter (variability of neighboring muscle fibers) on single fiber EMG
Tx: thymectomy, pyridostigmine (ACh-esterase inhibitor), plasmapheresis/IVIG
LEMS - EDX
r/o small cell lung ca
NCS: low amplitude CMAPs bc hard to get response
normal RNS
EMG: increased jitter and blocking on single fiber EMG
Tx: rehab, corticosteroids, anticancer therapy, plasmapheresis/IVIG
botulism - EDX
NCS: decreased/absent CMAP, abnormal RNS
EMG: active denervation w decreased recruitment, increased jitter on single-fiber EMG
Tx: antitoxin, rehab, respiratory support
RNS - EDX indications, findings/Dx
when NMJ disorder suspected
normal people: CMAP looks fine
NMJ disorder: CMAP amplitude will decreased
>10% decrement between 1st and 4th waveforms is positive for NMJ disease
RNS can be given at low rate or high rate
low v high rate RNS
low: muscle stimulated at 2-3 Hz; NMJ dz will cause amplitude decrement
high: muscle stimluated at 10-50 Hz
Ca builds up in neuron → facilitates normal NMJ transmission → normal CMAP
all NMJ dz will show some CMAP repair, but with LEMS it will show huge increase in CMAP amplitude (300%)
post exercise facilitation v exhaustion
similar to RNS
facilitation: like high rate RNS
after low rate RNS → maximal contraction, 60 seconds → repair of CMAP
exhaustion: CMAP decreased the more a person exercises overall
after low rate RNS → CMAP does not show decrement → if still suspect NMJ dz → repeat low rate RNS q1min x5mins → one test should show CMAP decrement
anterior horn cell dz - EDX
PE: usually LMN signs, sometimes UMN present (ALS, PLS, HSP)
in general, SNAPs normal as well as latency/CV (not demyelinating but axonal loss)
must demonstrate abnormalities in 3 out of 4 spinal segments (cervical, thoracic, lumbosacral)
e.g., SMA, ALS, poliomyelitis, post-polio syndrome
SMA - Px/course/EDX
mutations in SMN1 gene →
SMA1 (Werdnig-Hoffman): floppy infant, dies of resp failure
SMA2: weak 1 year old, wheelchair as toddler, can sit independently and stand w ADs, dies of respiratory failure
SMA3: gradually weakning ~10 year old, can walk independently, normal life expectancy
labs: elevated CK
EDX: normal SNAPs, abnormal CMAPs, LDLA MUAPs w decreased recruitment
Tx: rehab, nusinersen, Zolgensma
ALS -Px/EDX
60 year old, progressive weakness w UMN/LMN signs (pure motor), no bowel/bladder abnormalities
NCS: normal SNAPs, possibly normal CMAPs d/t reinnervation
EMG: LDLA MUAPs, decreased recruitment, fibs/sharps, increased jitter and fiber densitiy
show denervation in 3 of 4 spinal segments
Tx: rehab, submaximal exercise, riluzole (anti-glutamate)
poliomyelitis - EDX
pure motor anterior horn degeneration following polio infection
NCS: normal SNAPs, decreased amplitude CMAPs
EMG: LDLA MUAPs, fibs/sharps, decreased recruitment
Tx: supportive
post-polio syndrome
clinical Dx, no EDX required
Px: new onset progressive weakness
Hx: prior recovery from polio 15 years ago
remaining anterior horn cells get burnt out
if EDX:
NCS: normal SNAPs, low amplitude CMAPs
EMG: giant MUAPs, decreased recruitment, fibs/sharps
myopathy - Dx/EDX
muscle Bx can show type I (aerobic) or type II (anaerobic) muscle fiber atrophy
type II atrophy usually w steroid myopathy
EMG only evaluates type I fibers → will appear normal with steroid myopathy
EDX:
NCS: normal SNAPs, abnormal CMAP amplitude d/t atrophied muscles
EMG: SDSA polyphasic MUAPs (myopathic motor units); muscle so atrophied and small that takes early/increased recruitment to summate for muscle contraction
myotonic discharges divebomber sound
Gottron papules
purple patches over MCPs/PIPs/DIPs
associated w heliotrope trash
inflammatory myopathy (e.g., dermatomyositis, polymyositis)
Hx viral infection/cancer
dermatomyositis/polymyositis - Px/Dx/EDX
Hx viral infection/cancer
“type 3 not me” type 3 = cancer
proximal weakness +/- heliotrope rash and Grotton papules (purple patches of MCP/PIP/DIP)
labs: elevated CK, ESR, LDH; perifasicular atrophy on muscle Bx
NCS: normal SNAPs and CMAPs
EMG: abnormal MUAPs (SDSA w increased/early recruitment)
Tx: corticosteroids, plasmapheresis/IVIG
statin myopathy
stop offending agent, can slowly reintroduce or switch to other statin
proximal muscle pain (myalgias), Hx statin use, often iso CYP450 inhibitors
NCS: normal SNAPs and CMAPs
EMG: normal
steroid myopathy
causes type II muscle atrophy (Bx)
NCS/EMG: normal
critical illness myopathy
Hx: patients in ICU; weakness and atrophy in both proximal and distal muscles with normal sensation; thus not critical illness neuropathy or AIDP
labs: elevated CK (muscle dz)
NCS: normal SNAPs, low amplitude CMAPs
EMG: SDSA MUAPs, sometimes fibs/sharps, with normal/early recruitment
