Indications for LP?
- emergent
- general
Emergent:
- suspected CNS infection
- suspected subarachnoid hemorrhage in a pt w/ negative CT scan
General:
- dx of CNS malignancies
- demyelinating dz
- guillain barre syndrome
- introduce drugs into the subarachnoid space for tx of cancer or contrast agents.
Site of LP? Explain procedure.
L3-L4 or L4-L5
pt in left lateral decubitus fetal position or sitting upright with spine curved forward, entry through L3/L4 or L4/L5 space. measure opening pressure with manometer, collect 8-15cc of CSF in 4 tubes
LP:
- relative CI
- complications
CI:
- local skin infections over puncture site
- increased ICP; exception is pseudotumor cerebri
- suspected spinal cord mass or intracranial mass lesion
- uncontrolled bleeding predisopsition, thrombocytopenia, or anticoagulation
- spinal column deformities
- suspected spinal epidural abscess
- lack of pt cooperation
Complications:
- post LP HA (CSF leak)
- infection
- bleeding (spinal hematoma)
- cerebral herniation
- minor neurological sx (radicular pain or numbness)
- late onset epidermoid tumors of the thecal sac
- back pain
You need to rule out mass lesion causing increased ICP prior to performing and LP, what are some high risk sx for increased ICP that would require CT of the head prior to LP?
- altered mentation
- focal neurologic signs
- papilledema
- seizure within the previous week
- impaired cellular immunity
What are the CSF Normal Values:
- Pressure
- appearance
- total protein
- glucose
- cell count and diff
- opening pressure
Pressure: 70-180mmH20
Appearance: clear, colorless
total protein: 15-45mg/dL
glucose: 45-85mg/dL or greater than 2/3 of serum blood glucose
Cell count & diff: WBC: 0-5cells/uL
RBC: 0
Opening pressure: 70-180MMH20; increases with increased BMI
CSF Analysis: Appearance:
-what is xanthochromia? What may cause this? What colors might be present and what do they represent?
yellow, orange, or pink from lysis of RBC. May be caused by subarachnoid hemorrhage, increased protein levels, elevated bilirubin.
Yellow: blood breakdown products or hyperbilirubinemia, CSF protein greater than 150mg/dL
Orange: blood breakdown products or high carotenoid ingestion
Pink: blood breakdown products
Green: hyperbilirubinemia, purulent CSF
Brown: meningeal melanomatosis (Melanoma of the CNS)
What is one of the most sensitive indicators of pathology within the CNS?
CSF protein.
CSF Analysis: Protein
-why might this be low? elevated?
Low: repeated LPs, CSF leak, acute water intoxication
Elevated: infections, intracranial hemorrhage, multiple sclerosis, Guillain barre, malignancy, some endocrine abnormalities, inflamm conditions, falsely elevated traumatic tap
CSF analysis: Glucose
-what might cause low and high CSF glucose?
Low: bacterial infection, neoplasm, or fungal infection.
High: when peripheral glucose levels are elevated
*can be normal in viral infection.
CSF analysis: Cell Count
-when might WBC be increased or decreased?
WBC:
-increased: post seizure, ICH, malignancy, inflamm conditions, greater than 1000 more likely bacterial meningitis
-decreased: less than 1000 is more likely viral meningitis
CSF analysis: cell differentail
-normal WBC % of lymphocytes and moncytes?
- meningitis with predominance of neutrophils is caused by what?
- meningitis with predominance of lymphocytes is caued by what?
- increased eosinophils may indicate what type of infection?
Normal WBC:
70% Lymphocytes, 30% monocytes
Neutrophils = bacteria
Lymphocytes= viral, fungal, TB
Eosinophil = parasitic infection
CSF analysis: cell count
-when might you see RBCS?
-traumatic tap; measure cell counts in 3 consecutive tubes an the number of RBC should decrease with each, if they dont then assume from intracranial hemorrhage.
Microscopic Examination of CSF: what would each of the following tests reveal?
- acid fast stain
- india ink
- wright or giemsa
Acid fast: TB
India ink: cryptococcus
Wright/giemsa: toxoplasmosis
How might Latex agglutination and PCR be useful in examination of CSF?
Latex agglutination: allows for rapid detection of bacterial antigens in CSF, variable sensitivity and specificity
PCR:
- high sensitivity and specificity
- fast
- useful in viral meningitis, HSV-1, EBV, enterovirus, CMV, TB, acute neurosyphilis
Nerve Conduction Studies:
- what are the two types?
- what do each of them measure?
- what is the utility of theses tests?
Nerve conduction velocity: measure how well and how fast the peripheral nerves send the signals.
Electromyelography: measures the electrical activity of muscles during rest and contraction
Utility:
-both tests are done together to sort out if there is a nerve signal problem or is the muscle just not responding?
(e. g. is the nerve signal adequate but the muscle is not responding vs. altered nerve signals and intact muscle response. )
- characterize disorders of the motor neuron, NMJ, primary nerve disorder or nerve root disorders
What are the three types of nerve fibers?
A-alpha: large myelinated, senses touch, vibration, position
A-delta: small myelinated fibers, senses cold and pain
C fibers: unmyelinated fibers, sense warm and pain
Indications for EMG and Nerve conduction velocity?
WHat are some disorders that can be diagnosed by nerve conduction velocity studies?
nerve conduction study velocity can only study which nerve fibers?
- evaluation of paresthesias of the arms and legs
- evaluate weakness of the arms and legs
Disorders:
-carpal tunnel, ulnar neuropathy, spinal disc herniation, guillian barre, peripheral neuropathy, Myasthenia Gravis
Nerve conduction velocity can only study the largest A-alpha fibers, so if you have neuropathy of the A-delta small fibers the test can be normal
Nerve conduction velocity is useful in studying what types of neuropathy?
How will nerve conduction velocity be impacted if demyelination is present?
- demyelinating polyneuropathy (e.g guillian barre) or focal demyelination (e.g carpal tunnel)
- these both slow down velocity
There will be slow conduction velocity if demyelination or destruction of large fibers.
EMG:
- use?
- example of disorders dx
- how is this done?
Use: finds diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle
-herniated disc, amyotrophic lateral sclerosis, or myasthenia gravis
How:
-needle placed into muscle and electrical stimulus is delivered to create an action potential.
Electroencaphalogram (EEG)
- clinical utility
- how does this work?
Utility:
-to distinguish epileptic seizures from psychogenic spells, syncope, movement disorders, migraine variants
- differentiate organic causes of encephalopathy or delerium from psychiatric causes
- test for brain death
- determine whether or not to wean anti-epileptic meds
Work:
-10-20electrodes on the scalp record the synaptic activity of the brain, this is recorded as a wave form.
*Wave forms are labeled according to their amplitude;
Delta: 0-4Hz, Theta: 4-8Hz, Alpha 8-12Hz, Beta greater than 12hz
EEG:
-what might increased slow wave activity in an awake patient mean? What waveforms present?
slow wave activity in an awake patient is demonstrated by theta and delta waves indicating a focal brain lesion.
- focal delta activity is usually irregular in configuration and is termed polymorphic delta activity (PDA)
- increased slow wave activity when awake is virtually always abnormal!
PDA = focal brain lesion.
Generalized _____ and ____ activity is an indication of encephalopathy.
EEG is very useful in the dx of seizure disorders, T/F?
theta and delta
True.
WHat are some common EEG techniques used to induce epileptic activity?
- hyperventillation
- photic stimulation
- sleep
- sleep deprivation
- drugs
What three disorders are EEGs commonly used for dx?
Can a normal EEG rule out epilepsy?
Seizures, focal brain lesions, encephalopathy
No, a normal EEG does not rule out epilepsy
