Neurodiagnostics

Question 1

Site of puncture

Answer 1

L3-L4 or L4-L5

Collect 8-15 cc of cerebral spinal fluid in 4 tubes for lab studies

Question 2

Relative Contraindications to LP

Answer 2

*Local skin infections over proposed puncture site (absolute contraindication)
*Increased intracranial pressure (ICP); exception is pseudotumor cerebri
Suspected spinal cord mass or intracranial mass lesion
Uncontrolled bleeding diathesis, thrombocytopenia or anticoagulation
Spinal column deformities
Suspected spinal epidural abscess
Lack of patient cooperation

Question 3

LP Complications

Answer 3

Post lumbar puncture headache (10-30%)
Infection
Bleeding (Spinal hematoma)
Cerebral herniation (fatal)
Minor neurologic symptoms (radicular pain or numbness)
Late onset epidermoid tumors of the thecal sac
Back pain

Question 4

CSF normal values

Answer 4

Pressure: 70-150 mmHg (can be up to 250 in obese pts)
Cell count & differential:
WBCs: 0-5 cells/µL
RBCs: 0
Clear, Colorless
Protein: Newborns (up to 150 mg/dL), Adults (15-45 mg/dL)…CSF protein concentration is one of the most sensitive indicators of pathology within the CNS
the CSF glucose level is about 2/3 of the serum glucose measured during the preceding 2-4 hours

Question 5

Xanthochromia

Answer 5

Yellow: Blood breakdown products, hyperbilirubinemia, CSF protein > 150 mg/dL, > 100,000 rbcs per mm3
Orange: Blood breakdown products, high carotenoid ingestion
Pink: Blood breakdown products
Green: Hyperbilirubinemia, purulent CSF
Brown: Meningeal melanomatosis (Melanoma of the CNS)

Question 6

Classification of nerve fibers

Answer 6

A-alpha:
Large myelinated fibers
Touch, vibration, position	
A-delta:
Small myelinated fibers
Cold and pain sensation
C fibers:
Unmyelinated fibers
Warm and pain

Question 7

Nerve conduction velocity

Answer 7

Nerve conduction velocity can only study the largest A-alpha fibers
Tests motor and sensory nerves
Can appear normal in polyneuropathies with primarily small fiber involvement
Useful in demyelination conditions

Question 8

EMG

Answer 8

Find diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle
Herniated disc, amyotrophic lateral sclerosis (ALS) or myasthenia gravis

Question 9

Clinical utility of EEG

Answer 9

To distinguish epileptic seizures from: Psycogenic spells, syncope, movement disorders, migraine variants
Testing for brain death
Determining whether or not to wean anti-epileptic meds

Question 10

Increased slow wave activity in an awake pt may Equal…

Answer 10

focal brain lesion
Increased slow activity: theta and delta waves
Increased slow wave activity when awake is virtually always abnormal
Focal delta activity is usually irregular in configuration and is termed polymorphic delta activity (PDA)
PDA is usually indicative of a focal brain lesion