Neurologic Investigations Flashcards
What produces the CSF and what absorbs it?
choroid plexus of ventricles makes it, the villi of the arachnoid granulations in the dural venous sinuses absorb it
What disc interspace is typically used for an LP? What anatomical landmark can help you find it?
L3-L4 or L4-L5
the anterosuperior iliac spine is at the level of the L3-4 vertebral interspace
What are the contraindications for LP?
presence of a space-occupying lesion that is causing a mass effect with raised intracranial pressure, local infection or inflammation at the planned puncture site, or significant/uncorrected coagulopathy
What is the best position to place the patient in for an LP?
lateral recumbent position with the legs flexed up over the abdomen, pillow between the legs
How should the glucose of the CSF compare to that of the blood?
should be 2/3 that of blood
What is a normal protein level in CSF?
40-50 ml/dL
How many WBCs is considered normal in CSF?
less than 5
What is the normal opening pressure?
60-150 mmH2O
How can you tell if RBCs in the CSF is due to an actual bleed or just trauma from putting the LP needle in?
If there’s an actual hemorrhage there should also be xanthochromia
You should usually do a CT before doing an LP to look for mass lesion that might cause herniation, but what’s the situation where you should go straight to LP?
with suspected bacterial meningitis
What is the most common complication of an LP and how can it be treated?
low-pressure headache
have the patient lie flat and increase his or her intake of liquids and caffeine. Rarely, it may be necessary to administer an epidural blood patch
What type of WBCs will predominate with a bacterial infection? (except in what type of bacterial infection?)
polymorphs
except in tuberculous meningitis, which has lymphocytes predominating
What type of WBCs will predominate with a viral infection?
lymphocytes
What type of WBCs will predominate with demyelination like MS or ADEM?
lymphocytes
A positive EBV PCR on CSF is highly suggestive of what?
CNS lymphoma in patients with AIDS or other immunosuppression
For MRI….what’s bright on T1 and what’s bright on T2?
T1 - fat is bright
T2 - water (and CSF) is bright
Which one - T1 or T2 - is better at evaluating the spinal cord?
t2
What is the contrast agent used in MRI?
gadolinium
Are gad-enhanced images usually acquired with T1 or T2?
T1
What do we use gad to see?
brain tumors, abscesses (and other areas of inflammation) and new MS lesions
What is FLAIR?
It’s a strong T2-weighted image, but the signal from the CSF is inverted and thus is low rather than high intensity
***FLAIR is the single best screening image sequence for most pathologic processes of the CNS
What is susceptibility-weighted imaging good for?
it’s sensitive to the disruptive effects of a substance on the local magnetic field, so it will show blood breakdown products like ferritin and hemosiderin (will appear black)
What is diffusion-weighted imaging good for?
It demonstrates cellular toxicity with a high sensitivity
most commonly employed in the diagnosis of ACUTE stroke
How soon after an acute stroke will DWI be positive?
within a half hour of symptom onset!
Will areas of restricted diffusion appear bright or dark on DWI?
bright
Which imaging - MRI or CT should you use to look for fresh blood?
CT (without contrast)
Which imaging - MRI or CT - should you use to look at the posterior fossa and craniocervical junction?
MRI because you can’t seen it well on CT due to the artifact of surrounding bone
What is the “gold standard” in cerebral vascular imaging?
conventional angiography (even though MRA is growing more popular)
What are the benefits to MRA or conventional angiography?
it’s less invasive (bc you don’t need to inject a contrast agent - the blood flow is the contrast in MRA)
can be done more quickly
cheaper
just less sensitive/specific
What is the typical clinical scenario for using MRA?
stroke
What are you looking for if you use a “fat-suppressed” MRA of the neck?
vertebral or carotid artery dissections
What are you looking for if you do MR venography?
venous sinus thrombosis
What will PET show in people with epilepsy?
hypermetabolism during the seizures, hypometabolism post-ictally
What will PET show in alzheimer’s disease?
hypometabolism in the temporal and parietal lobes
What will PET show in frontotemporal dementia?
hypometabolism in the frontal and temporal regions
What will PET show in dementia with Lewy bodies?
hypometabolism in the occipital lobes
What type of CT uses a radioactive isotope to demonstrate increased blood flow during seizures or decreased blood flow in the degenerative dementias?
Single-photon emission CT (SPECT)
Rank the typical EEG frequency patterns (alpha, beta, delta, theta) in terms of their frequency from lowest to highest.
delta (0.5 - 3 Hz)
theta (4-7 Hz)
alpha (8-13 Hz)
beta 14-30 Hz)
What are the two types of montages for EEG? How do they differ?
bipolar and referential
bipolar: all the electrodes are active and a recording is made of the difference in electrical activity between two adjacent electrodes
referential: the electrical activity is recorded beneath the active electrode relative to a distant electrode or common average signal
What are three major limitations of EEG?
- patterns are almost never specific to their causes
- EEG can only record cortical neurons
- can only give a measure of cortical activity at the time of recording and can be normal in between episodes
Focal arrhythmic, polymorphic slow activity in the theta or delta range is commonly caused by what?
vascular disease causing local dysfunction
Generalized arrhythmic slow activity often indicates what?
diffuse encephalopathy
What are the most common EEG patterns of seizures?
rhythmic spike or sharp and slow wave discharges or rhythmic slow waves
WHat is the dominant EEG pattern during the awake, resting state with eyes closed?
alpha (8-13 Hz)
Visual evoked potentials is used primarily in the diagnosis of optic neuritis and MS. What would be a positive result?
a delay in the P100 potential suggests dysfunction of the optic nerve
Somatosensory evoked potentials may be used to assess anoxic brain damage. What result indicates a very poor prognosis in coma patients”
absence of the N20 potentials
Brainstem auditory evoked potentials are useful to assess brainstem dysfunction, particularly in patients with what tumor?
vestibular schwannomas
What are the three variables that are measured in motor nerve conduction studies?
distal latency (how long it takes between stimulation and contraction)
conduction velocity
Compound muscle action potential (contraction)
What can repetitive nerve-stimulation studies demonstrate?
either decremental or incremental CMAP responses in disorders of the neuromuscular jucntion
Electromyography involves the insertion of a needle into individual muscles. What are the three types of recordings that are made?
- insertional activity
- spontaneous activity (while muscle is at rest)
- Volitional motor unit potentials (during contraction)
What are the two things a muscle can do to contract more strongly?
the motor units can fire more quickly (activation)
they can add more motor units (recruitment)
Which one shows reduced activation and which one shows reduced recruitment - CNS disease or PNS disease?
CNS has reduced activation
PNS has reduced recruitment
What are the EMG hallmarks of NMJ disease?
increased jitter and blocking
whatever the hell those are…
What happens to insertional activity in neurogenic disease? in myopathic disease?
neurogenic: increased
myopathic: usually normal
What happens to spontaneous activity in neurogenic disease? Myopathic disease?
neurogenic: increased
myopathic: usually normal
What happens to volitional motor unit potentials in neurogenic disease? myopathic disease?
neurogenic: large amplitude/polyphasic
myopathic: small amplitude/polyphasic
How can you differentiate a demyelinating neuropathy from an axonal neuropathy using nerve conduction studies?
distal latency will be markedly prolonged in demyelinating (make sense)
conduction velocity will be markedly reduced in demyelinating (makes sense)
CMAP amplitude will be normal in demyelinating but reduced in axonal (makes sense)
MAKES SENSE
