Neuordiagnostics

Question 1

Indications for lumbar puncture?

Answer 1

• when CSF is needed for biochemical analysis, cellular exam and culture
• also done to introduce drugs into subarachnoid space for tx of cancer or to introduce contrast agents

-emergent indications:
suspected CNS infection,
supected subarachnoid hemorrhage in pt with neg CT scan

general indications:
dx of CNS malignancies, demylenating diseases, Guillain-Barre syndrome

Question 2

Site of LP?

Answer 2

• L3-L4 or L4-L5

Question 3

Technique of LP?

Answer 3

• pt in left lateral decubitus fetal position or sitting upright with spine curved forward
• entry through L3-L4 or L4-L5 space using sterile technique
• measure opening pressure with manometer (best if pt in recumbent position)
• collect 8-15 cc of CSF in 4 tubes for lab studies

Question 4

What are some relative CIs to LP?

Answer 4

• local skin infections over proposed puncture site (absolute CI)
• IICP, exception is pseudotumor cerebri (cause herniation of brain)
• suspected spinal cord mass or intracranial mass lesion (based on lateralizing neuro findings or papilledema)
• uncontrolled bleeding diathesis, thrombocytopenia, or anitcoag
• spinal column deformities (osteoarthritis) (may reqr fluoroscopic assistance)
• lack of pt cooperation

Question 5

Complications of LP?

Answer 5

• post lumbar puncture HA (10-30% of pts): CSF leak - go away when lying down
• infection
• bleeding: spinal hematoma
• cerebral herniation (fatal)
• minor neuro sxs (radicular pain or numbness)
• late onset epidermoid tumors of the theca sac
• back pain

Question 6

What pts should undergo a CT of head prior to LP?

Answer 6

- pts that you want to R/O mass lesion:
altered mentation
focal neuro signs
papilledema
seizure w/in previous week
impaired cellular immunity (cancer)

• some places have protocols where CT is done on all pts prior to LP

Question 7

CSF normal values?

Answer 7

• pressure: 70-180 mmH2O (can be up to 250 in obese people)
• appearance: clear, colorless
• total protein: 15-45 mg/dL
• glucose: 45-85 mg/dL or greater than 2/3 of serum blood glucose
• cell count and diff: WBCs - 0-5 cells/microL, 0 RBCs

Question 8

Opening pressure - CSF analysis?

Answer 8

• normal: 70-180 mmH2O but increases with BMI
• need to be in lateral decubitus position to measure accurately
• elevated ICP can be present in meningitis, ICH, tumors
• will be on high end in obese pts

Question 9

Appearance - CSF analysis?

Answer 9

• normal is crystal clear
• may be cloudy from infection, bloody or colored:
  bloody tap or
  xanthochromia = yellow, orange, or pink from lysis of RBCs (occurs w/in 2 hrs, last 2 weeks) - subarachnoid hemorrhage, increased protein levels, elevated bilirubin

Question 10

Different causes of Xanthochromia? yellow?

Answer 10

• blood breakdown products, hyperbilirubinemia, CSF protein greater than 150 mg/dL, greater than 100,000 rbcs/mm3

Question 11

Xanthochromia - orange?

Answer 11

• blood breakdown products, high carotenoi ingestion

Question 12

Xanthochromia - pink?

Answer 12

• blood breakdown products

Question 13

Xanthochromia - green?

Answer 13

• hyperbilirubinemia, purulent CSF

Question 14

Xanthochromia - brown?

Answer 14

• meningeal melanomatosis (melanoma of CNS)

Question 15

CSF anaylsis: protein?

Answer 15

• CSF protein concentration is one of most sensitive indicators of pathology within CNS
• newborns: up to 150 mg/dL
• adults (15-45 mg/dL), same for kids at 6-12 months
• can diff protein types for conditions such as Guillan Barre and MS
• low: repeated LPs, CSF leak, acute water intoxication
• elevated: infections, ICH, Guillain Barre, malignancy, some endocrine abnormalities, inflammatory conditions
• falsely elev in traumatic tap: correction factor - subtract 1 mg/dL for q 1000 RBCs

Question 16

CSF analysis - glucose?

Answer 16

• glucose level is about 2/3 serum glucocse measured during preceding 2-4 hrs
• normal: can be normal in CNS viral infection
• low: CNS bacterial infection, neoplasm or fungal infection
• high: when peripheral glucose levels are elevated, above a serum glucose of 300 the CSF glucose doesn’t increase that much

Question 17

CSF analysis - WBCs

Answer 17

• WBCs:
  0-5 mm3 adults, up to 20 mm3 in newborns
• meningitis: less than 1000 likely viral, and greater than 1000 likely bacterial
• increased post seizure, ICH, malignancy, inflammatory conditions

Question 18

CSF analysis - cell diff?

Answer 18

• normal WBC 70% lymphocytes, 30% monocytes
• in meningitis: predominance of neutrophils= bacterial
• in meningitis: predominance of lymphocytes = viral, fungal or TB
• increased eosinophils = parasitic infection

Question 19

CSF analysis - RBCs?

Answer 19

• traumatic tap: measure cell counts in 3 consecutive tubes and number of RBCs should decrease with each
• if RBCs don’t decrease then assume from intracranial hemorrhage!!!

Question 20

Microscopic exam?

Answer 20

• gram stain
• acid fast stain for TB
• india ink stain positive in cryptococcus
• wright or giemsa stain + in toxoplasmosis

Question 21

Other tests with LP (latex agglutination, PCR)?

Answer 21

• send for culture
• latex agglutination: allows for rapid detection of bacterial antigens in CSF, variable sensitivity and specificity
• PCR: high sensitivity and specificity, fast, particularly useful in viral meningitis, HSV-1, EBV, enterovirus, CMV, TB, acute neurosyphilis

Question 22

Expected LP results in bacterial meningitis?

Answer 22

• pressure of over 300 mmH20
• cloudy, purulent
• increased total protein
• decreased glucose
• greater than 1000 cell count, greater than 80% are neutrophils

Question 23

Expected LP results in viral (aseptic meningitis)?

Answer 23

• over 200 mmH2O
• clear
• increased total protein
• normal glucose
• increased cell count, but less than 1000 (lymph up to 50%)

Question 24

Expected LP results in fungal meningitis?

Answer 24

• over 300 mmH2O
• clear or cloudy
• increased total protein
• decreased glucose
• increase but less than 500 cell count, lymph up to 50%

Question 25

Multiple sclerosis findings in LP?

Answer 25

- normal pressure - clear color - increased total protein - increased WBC 0-20 (lymph)

Question 26

Guillian-Barre findings in LP?

Answer 26

- normal pressure - clear or xantho colore - increased total protein - normal glucose - normal or elevated cell count

Question 27

2 diff types of nerve conduction studies?

Answer 27

- Nerve Conduction Velocity (NCV): measures how well and how fast the peripheral nerves send the signals - eval of entrapment neuropathies and Guillian Barre - electromyelography (EMG): measures the electrical activity of muscles during rest and contraction

Question 28

What are nerve conduction studies?

Answer 28

- test the peripheral nerves only and can dx a focal or generalized disorder - used to diff muscle disorders from nerve disorders - Use to figure out if the nerve signal is adequate but muscle isn't responding vs altered nerve signals and intact muscle response

Question 29

Indications of nerve conduction studies?

Answer 29

- eval of paresthesias of arms and legs - eval of weakness of arms and legs - some disorders that can be dx by nerve conduction studies: carpal tunnel, ulnar neuropathy, spinal disc herniation, Guillian Barre, peripheral neuropathy - myasthenia gravis

Question 30

Classification of nerve fibers?

Answer 30

- A-alpha: large, myelinated fibers, touch, vibration and position - A-delta: small myelinated fibers, cold and pain sensation - C-fibers: unmyelinated fibers, warm and pain

Question 31

What is NCV? What does it study? Limitations? Useful in testing for what diseases?

Answer 31

- only study the largest A-alpha fibers: touch, vibration and position - tests motor and sensory nerves - can appear normal in polyneuropathies with primarily small fiber involvement - stim of motor or sensory nerve at diff pts and calculation of velocity of conduction of propagated impulse - measures velocity of fastest conducting fibers - normal velocity if myelin is intact - slow conduction velocity if demylenation or destruction of large fibers - Useful in studying demyelinating polyneuropathy (Guillain-Barre syndrome) or focal demyelination (entrapment neuropathies such as carpal tunnel syndrome)

Question 32

Indications for EMG?

Answer 32

- find diseases that damage msucle tissue, nerves, or junctions b/t nerve and muscle - herniated disc, amyotrophic lateral sclerosis (ALS) or myasthenia gravis - involves cooperative pt who can voluntarily contract muscles when needed (it does hurt!) - needle electrodes are used (surface EMG unreliable)

Question 33

Mechanism of EMG?

Answer 33

- needle is placed into muslce (motor unit) | - electrical stimulus delivered and a motor unit AP is created

Question 34

Use of nerve conduction tests?

Answer 34

- should always be ordered together (EMG and NCV) - may be used to dx or follow progression of various diseases - consider for eval of peripheral weakness and or parasthesias - characterizes disorders of motor neuron, neuromuscular jxn, primary nerve disorder or nerve root disorders - ** these shouldn't be first tests ordered but should be used to confirm a dx or judge severity of disease

Question 35

Clinical utility of EEG?

Answer 35

- to distinguish epileptic seizures from: psychogenic spells, syncope, movement disorders, migraine variants - diff organic causes of encephalopathy or delirium from psychiatric causes - testing for brain death - determining whether or not to wean anti-epileptic meds (not having seizures anymore)

Question 36

Setup of electrodes in an EEG?

Answer 36

- consists of 10-20 electrodes and a nasopharyngeal lead that is placed in nose and advanced to pharynx near the temporal lobe - electrodes on the scalp record synaptic activtiy of the brain - electrical activity is recorded as a wave form - the wave forms are labeled according to their amplitude: delta - 0.4 Hz, theta 4-8 Hz, alpha 8-12 Hz, beta is greater than 12 Hz

Question 37

What does increased slow wave activity in an awake person mean?

Answer 37

- may be focal brain lesion theta and delta wves - increased slow waves - abnormal - focal delta activity is usually irregular in configuration and is termed polymorphic delta activity (PDA- usually indicative of focal brain lesion)

Question 38

What is EEG a sensitive test for?

Answer 38

- for encephalopathy - gen. theta and delta activity is an indication of encephalopathy - also very useful in dx of seizure disorders, epileptiform d/c's are common b/t overt seizures as well as during seizures

Question 39

What events can induce seizures, thus increasing EEG test sensitivity?

Answer 39

- hyperventilation, photic stimulation, sleep, sleep deprivation, drugs

Question 40

When is an EEG used?

Answer 40

- commonly used to work up seizure disorder - able to dx seizures, encephalopathy, focal brain lesions - However, normal EEG doesn't rule out epilepsy (possible to miss infrequent epileptic activity - try for multiple recordings)