Board prep - Neuromuscular focus Flashcards
Describe corynebacterium neuropathy and treatment
Diptheria
Differentiate GBS from the. following:
- polio
- tick paralysis
- porphyria
- diptheria
Rules of GBS:
- Abdominal pain should PRECEDE but not occur simultaneously with weakness
- GBS is a pure nerve d/o»_space; you should not see AMS
- CSF finding is albuminocytologic dissociation: high protein, LOW wbc
Diptheria may have more of descending quality
CIDP criteria duration
More than 2 months (>56 days)
Describe CIDP features
Usually motor + sensory
Describe Lewis-Sumner syndrome (MADSAM)
Variant of CIDP which affects asymmetrically the UPPER extremities first
Multifocal conduction block
Responds well to IVIG
Often confused with mononeuropathy multiplex - look for demyelinating features
Describe DADS
Distal Acquired Demyelinating Syndrome often associated with IgM monoclonal gammopathy particularly anti-MAG
Poor response to treatment
What are first-line treatment options for CIDP? How is this different from GBS?
Oral/IV prednisone (unlike GBS/AIDP!!!)
IVIG
Others: azathioprine, cyclosporine, methotrexate
Interpret this motor - NCS
Looking at distal to proximal there is a significant reduction in the size of CMAP c/w a conduction block (drop >50%)
Whenever you see a conduction block think about multifocal motor neuropathy
Speed associations:
Conduction block - dx?
Multifocal motor neuropathy
What are some features of multifocal motor neuropathy?
Male-predominant autoimmune disorder with weakness exceeding atrophy, often upper limb before lower limb and distal more than proximal
Often mimic of ALS because MMN is VERY treatable. Patients with MMN don’t have any upper motor neuron findings
Like GBS steroids are INEFFECTIVE (unlike CIDP)
Multifocal motor neuropathy with conduction block associated antibody
Anti-GM1 (only present in 50%) but another way to differentiate from ALS
GM1 antibodies word of warning - markedly elevated antibodies highly associated with MMN
Intermediate and low range antibodies can be associated with aLS
How to clinically differentiate multifocal motor neuropathy and vasculitis neuropathies?
MMN - motor ONLY
Vasculitic neuropathy - motor AND PAIN, +weight loss, fatigue, arthralgias
Describe vasculitic neuropathies
BURNING
Asymmetric presentation of motor + sensory
Most patients >50yo
Clinical example: 52yo man presents for L wrist drop and subsequently develops R foot drop. He reports significant pain, weight loss, and fatigue. Reflexes are reduced. Focal atrophy of muscle examination. EMG/NCS is notable for asymmetric neuropathy with sensory and motor involvement.
Differentiate the following vasculitides:
- Polyarteritis nodosa
- Microscopic polyangiitis
- Churg-Strauss
- Wegener’s granulomatosis
10-30yo patient with:
- High arched feet
- Hammer toes
- Absent reflexes
- Inverted champagne bottle leg
- Prominent steppage gait
- EMG - markedly slow conduction velocities
Charcot-Marie-Tooth type 1
Autosomal DOMINANT disorder
Hereditary sensory and motor neuropathy (HSMN)
DEMYELINATING
Charcot-Marie-Tooth type 1A gene and inheritance
PMP-22 DUPLICATION (chr 17)
CMT type 1a vs type 1b
CMT type 1a is the more classic and favorite of the boards. Clinically type 1a and type 1b are almost indistinguishable. Type 1b has more “axonal” electrophysiologic features and more likely to be associated with Adie’s pupil
Genetics:
1a: AD PMP-22 duplication (chr 17)
1b: AD myelin protein zero (MPZ) duplication (chr 1)
Describe HNPP
Multiple mononeuropathies often with family hx usually precipitated by positioning
Important to differentiate from vascultitis neuropathies and mononeuritis multiplex:
- not painful
- starts in adolescence
- no other sx features of vasculitic neuropathy
- On US HNPP have sausage feature unlike vasculitic hypoechoic and enlarged
Describe CMT type 2
axonal!
Still AD
MFN2
Describe CMT type X
Differentiate CMT types by inheritance, gene, and neuropathy type:
- CMT 1a
- CMT 1b
- CMT 2
- CMT type X
Describe Refsum disease
What type of neuropathy is suggested by this nerve biopsy?
This is onion bulb sign reflecting demyelination and remyelination with multiple layers of Schwann cells around the axon
Clinical clues for a DEMYELINATING polyneuropathy
Early generalized loss of reflexes
Disproportionately mild muscle atrophy in presence of weakness
Neuropathic tremor
Palpably enlarged nerves
What is the following NCS demonstrating?
What type of neuropathy should that trigger?
Temporal dispersion which is indicative of ACQUIRED DEMYELINATION
(all the fibers aren’t getting together at the same time)
What is a SLOW conduction velocity in nerves of arms? Nerves of legs?
Arms <35m/s
Legs <30m/s
Board questions probably going to give you velocities in the 10s because there is no way axonal process could cause velocities that slow
Neurophysiologic findings in demyelinating neuropathy (5)
- MARKED slowing of conduction velocity (<50%, ie 10s)
- Distal latencies are MARKEDLY prolonged (>130%)
Acquired demyelination only - conduction block and temporal dispersion
Because the axon is still intact, there is little muscle atrophy
Unmyelinating fibers are unaffected so temp and pain sensation are typically spared
Describe the NCS findings below
Proximally higher amplitude with dramatic decrease to <50% = conduction block which is always indicative of ACQUIRED demylination
Polio vs GBS
CSF in polio has WBC
CSF in GBS has albuminocytologic dissociation
Describe tick paralysis
American dog tick poisoning include fever, chills and tender lymph nodes.In addition, American dog ticks can cause tick paralysis, which can lead to respiratory distress and muscle weakness.
Porphyria
5 P’s of porphyria
Pain
Psychiatric
Peripheral neuropathy
Pink urine
Precipitated - drugs, alcohol, severe fasting
Describe the following CIDP variants:
- MADSAM (Lewis-Sumner syndrome)
- DADS
Describe features of tetanus
C. tetani toxin is internalized by retrograde axonal transport to alpha motor neurons cell bodies in brainstem and spinal cord
Migrates to presynaptic membrane and blocks release of inhibitory glyvine and GABA. Disinhibits spinal reflex arc and increases the firing rate of alpha motor neurons producing rigidity. Sx: Trismus, risus sardonicus, opisthotonus, hypersympathetic state
Cranial-caudal presentation because short nerves are affected faster. 1-2 weeks after exposure
Mechanism of stiff person syndrome
GAD-65 blocks glutamate decarboxylase leading to excessive glutamate and LESS gaba (More excitation and LESS inhibition anterior horn cells)
Stiff Person Syndrome features
Describe a normal NEUROMUSCULAR synapse
action potential reaches the terminal button of a motor neuron
Ca influx
ACh is released
K channels open allowing +charge out and reset of resting potential
Describe location of action of the following dz in neuromuscular synapse:
- Botulism
- Myasthenia gravis
- Organophosphates
- Lambert Eaton P/Q Ca Ch Abs
- Neuromyotonia
Botulism forms (5)
- Classic - food - pre-formed
- Wound - bacteria produces toxic
- Infant - ingested spores produce the toxin
- Hidden - adult form of infant
- Iatrogenic w/ treatment
What is botulism impact on pupils?
Botulism toxin blocks acetylcholine release thereby blocking pupillary constriction
Features of Lambert-Eaton
Does NOT affect eyes
As more action potentials come down eventually enough Ca channels open so that Ach can be released (Augmentation effect)
Note that 3,4-diaminopyridine (Ampyra) blocks potassium facilitating Ca channel open
Lambert-Eaton syndrome characteristic EMG
Low baseline CMAP with increment upon stimulation - Facilitation of CMAP
Describe neuromyotonia aka Isaac syndrome
Autoimmune condition of stiffness + continuous muscle twitching + EMG high frequency trains (“pinging” and after discharges (due to delayed muscle relaxation)
Synthesis and break down of acetylcholine
Nicotinic and muscarinic receptor distribution
Where do the following toxins work in the neuromuscular junction?
- tetrodotoxin (puffer fish)
- magnesium
- botulism
- lathrotoxin (black widow)
- scorpion venum
- tick paralysis (depate)
- b-bungarotoxin (snakes)
- mushrooms
- curare
Tick paralysis vs GBS
Organophosphate poisoning
What are they at risk for years later??
Years later they are at risk for delayed peripheral neuropathy even with limited exposure (organophosphate induced demyelinating polyneuropathy)
After discharges almost pathognomonic on EMG
Potentially fatal - bronchorrhea and bronchospasm
SLUDGE or DUMBBELSS
S - salivation
L - lacrimation
U - urinary incontinence
D - diarrhea and diaphoresis
G - gi upset
E - emesis
D - diaphoresis
U - urination
M - miosis
B.- bradycardia
B - bronchorrhea
E - emesis/excitation
L - lacrimation
S - Salivation
S - seizures
Describe ciguatera symptoms
Exposed to fish in a question stem think about ciguatera vs mercury… if lots of symptoms, ciguatera
Anticholinergic toxidrome symptoms…
Scalloped tongue with ptosis should make you think…
MuSK variant of myasthenia gravis
Describe MuSK antibody myasthenia gravis
EMG findings for myasthenia gravis
CMAP NORMAL at baseline and decrement with repetitive stimulation because not enough ACh can bind so responses get smaller and smaller
Practice recommendation for thymectomy for MG
If think there is a thymoma - get it our
Respiratory precautions MG
Key points of congenital MG
Inherited NOT autoimmune
Can be delayed but sx usually present at birth
Most AR
NO ROLE for immunosuppression
Transient neonatal myasthenia
Key myopathy features
What are some patient factors and comorbidities that cause elevated CK levels?
Myopathies with:
- Normal CK
- Elevated CK
EMG features myopathy
The number of functioning muscle fibers in a motor unit DECREASES so the smaller unit results in shorter duration and amplitude MUAP but you recruit other small muscle fibers and have polyphasic appearance
Neuropathic vs myopathic EMG features
Neuropathic - large
Myopathic - small, polyphasic
True or false:
Fibrillations does not automatically imply neurogenic process
True:
Use motor recruitment and clinical story to help you
General myopathic changes on biopsy
Myopathy vs neuropathy
