Diagnostic tests

Question 1

What blood testing can be performed?

Answer 1

 Haematology
 infectious and inflammatory dx
 hyperviscosity (polycythaemia)
 inclusions (lysosomal storage dx)
 thrombocytopenia

 Biochemistry
 liver function (bile acid stimulation test, ammonia)
 glucose and fructosamine (weakness, seizures)
 electrolytes (Na, K, Ca – weakness, seizures)
 CK, AST (muscle damage)

 Endocrine (mainly for neuromuscular diseases)
 thyroid dysfunction
 adrenal dysfunction
 insulin

Question 2

What immune mediated dzs can be tested for?

Answer 2

 Acute phase proteins (such as C-reactive protein)
 can be used as aid for diagnosis and mainly monitoring of any immune-mediated dx but better documented for steroid responsive meningitis arteritis (SRMA)

 Acetylcholine receptor antibodies titres
 gold standard diagnostic tool for the acquired form of Myasthenia Gravis (immune-mediated form where there are high numbers of circulating Ach recept Ab blocking Ach recepts at post-synaptic membrane of N-M junction). BUT takes approx 2 weeks for resuls

 Type IIM antibodies titres
 gold standard diagnostic tool for Masticatory Muscle Myositis (MMM). In this immune-mediated dx, there are large numbers of circulating Abs against the type
2M muscle fibres (only existent in MMs)

Question 3

What tests give you a quick indication of if a pet has myasthenia gravis?

Answer 3

Edrophonium test
 IV administration of edrophonium chloride after collapse - fast acting cholinesterase inhibitor
Pet will get up immediately and be OK for a couple of mins then get weak again.
 can cause cholinergic crisis – bradycardia, salivation, miosis, dyspnoea, tremors – give atropine!

If edrophonium OOS, Neostigmine test
 slower-acting drug so pre-treat patient with neostigmine IV or IM and exercise
 pre-treatment with atropine advised

Question 4

What serological testing may be required?

Answer 4

Dogs - 
 Neospora
 Toxoplasma
 CDV
 Cryptococcus
 Tick-borne diseases…

Cats
FIV
 FeLV
 FIP
 Toxoplasma
 Cryptococcus

Question 5

Outline the assessment of CSF analysis

Answer 5

 not consistently affected in CNS disease
 depend on location and extent of CNS lesion
 meningeal and ependymal lesions vs.
 parenchymal, extradural and non-exfoliative
 cell count does not correlate with severity
 always prior to myelography
 collect sample caudal to lesion

Question 6

When is CSF analysis contraindicated

Answer 6

 ↑ICP:
 mental status
 pupil size and PLR
 abnormal postures
 vestibular eye movement

 clotting problems
 Chiari-like malformation
 AA instability or trauma

Question 7

What do you analyse in CSF?

Answer 7

 differential cell count
 cytology
 protein
 PCRs
 normal:
 ≤ 5 WBC/µl
 no RBC
 protein ≤ 30-45 mg/dl-

Question 8

Outline cervical CSF collection

Answer 8

 cerebellomedullary cistern
 lateral recumbency
 head 90°, nose parallel to table
 imaginary line between occipital
protuberance and the atlas wings
 1.5 inch needle, 21-22G

Question 9

Outline lumbar CSF collection

Answer 9

 lumbar subarachnoid space
 lateral recumbency
 L5-L6 in dogs & L6-L7 in cats (and small dogs)
 2.5-3.5 inch needle, 21-22G

Question 10

When may you see a neutrophilic pleocytosis on CSF?

Answer 10

 SRMA
 bacterial (intracellular)
 MUOs
 fungal
 FIP
 post myelography, haemorrhage, trauma, neoplasia

Question 11

When may you see a mononuclear pleocytosis

Answer 11

 MUOs
 CNS lymphoma
 viral (CDV)
 bacterial and SRMA (chronic)

Question 12

When may you see a mixed pleocytosis?

Answer 12

 MUOs
 bacterial and SRMA (chronic)
 fungal
 protozoal
 non-inflammatory dx (infarction)

Question 13

When may ultrasound be useful?

Answer 13

 to investigate possible:
 PSS
 systemic disease (e.g. strokes)
 neoplastic disease
 can be used in cases of suspected hydrocephalus
when fontanelle is still open but requires some experience…

Question 14

When may you see eosinophilic pleocytosis

Answer 14

 eosinophilic ME
 fungal
 protozoal
 parasitic

Question 15

What anomalous ddx are rads good for seeing?

Answer 15

 AA luxation
 transitional vertebrae
 abnormal no. of vertebrae
 hemivertebrae, block vertebrae, butterfly vertebrae

Question 16

How can rads be used to check for trauma

Answer 16

 Can see fractures and luxations
 orthogonal views, survey of all spine, chest and abdomen
 3 compartment model

Question 17

Where can myelography detect issues

Answer 17

 extradural

 intradural (extramedullary vs intramedullary)

Question 18

Outline the use of myelography

Answer 18

 mainly useful for IVDD, to guide surgery (which disc and which side)
 can detect some neoplasia (not intramedullary); not useful in cases of vascular, inflammatory and some types of traumatic injury (ANNE)
 possible complications:
 neurological deterioration
 seizures
 difficult technique (possible trauma to SC); non-diagnostic (if SC too swollen)

Question 19

Outline the use of CT

Answer 19

 several x-rays projected by circular anode and then
information collected by detectors – image can be
reconstructed from multiple projections
 brain, skull, tympanic bullae, spine, SC with myelography
 can use 3D reconstructions
 can administer IV contrast (taken up by blood vessels or any structures with disrupted vascular endothelium or BBB – inflammation, neoplasia)

Question 20

Outline the use of brain CT

Answer 20

 very good for trauma (better bony detail than MRI)
 good for haemorrhage and middle ear disease
 fair for most tumours (some may be difficult to see)
 challenging in cases of inflammatory, vascular and anomalous disease…
 not good for caudal fossa (beam hardening artefact from thick occipital bone)

Question 21

When is CT of the spine useful?

Answer 21

 mainly used to help interpret myelography
when this is difficult to interpret (swollen SC)
 some congenital/developmental abnormalities
 trauma

Question 22

What is the use of MRI?

Answer 22

 provides excellent ST contrast so can see all neural structures
 can see brain, CSF pathways, CNs, SC, nerve roots, bone, ST, muscle, etc!
 images can be generated in any plane and result from effects of magnetic field over protons in the tissue

Question 23

What are the different MRI sequences?

Answer 23

 T2-WI
- fluid and fat are bright
 FLAIR (fluid attenuated inverse recovery)
- suppresses free fluid (dark)
- fluid in cells (oedema) is bright
 T1-WI
- fluid is dark and fat is bright
- enhancement where BBB not intact (neoplasia, inflammation, blood vessels)
 GRE
- blood is black
- blood can be dark or bright in both T1 and T2 depending on how old bleed is – hard to be certain…
 good to look for haemorrhagic strokes and haemorrhage within lesions (e.g. suspicion of myelomalacia)
 STIR (Short T1 Inversion Recovery)
- suppresses fat
- good for bone and muscle changes (inflam, neoplasia) and to evaluate regions with significant amounts of fat (e.g. retrobulbar region)

Question 24

What is the use of electrodiagnostics?

Answer 24

 recording of electrical activity of muscles or neural structures
 can be spontaneous (EEG, EMG) or in response to stimulation (NCV)
 can evaluate neural tissue (brain, SC, PN), n-m junction and muscle
 most studies requite GA, some sedation
 often require biopsies afterwards

Question 25

Outline electromyography

Answer 25

 records spontaneous muscle electrical activity
 normal muscle at rest is electrically silent
 destabilization of the muscle cell membrane results is spontaneous discharge
 identifies denervated (around 7-14 days) or damaged muscles
 presence and distribution of lesions
 does not differentiate between muscle and nerve

Question 26

Outline nerve conduction velocities

Answer 26

 evaluates peripheral nerve function
 calculated by stimulating nerve at at least 2 different points and recording
• amplitude of response (strength)
• latency of response (how long it takes to get there – to calculate velocity)
 velocities (myelin)
 amplitude (axon)

Question 27

Outline F wave assessment

Answer 27

 to evaluate nerve roots and proximal part of PNs
 antidromic impulses of motor fibres travelling
nerve proximally towards ventral nerve root – SC
– same motor fibres distally until muscle
 purely motor

Question 28

Outline repetitive nerve stimulation

Answer 28

evaluates n-m junction (MG, botulism)
Tests nerve 10 times, there should be similar response each time. If the junction is abnormal there is a decreasing response.
V. good for congenital myasthenia gravis where there will not be antibodies to Ach receptors

Question 29

Outline the BAER

Answer 29

 click stimuli generated by either headphones
or insert earphones
 3 needle electrodes sample electrical responses of CNVIII and auditory portion of the brainstem and result in up to seven (I-VII) positive waves
 screening tool for detection of congenital sensorineural deafness
 determinate hearing threshold in adults
 assess neural lesions CNVIII or brainstem
 assess for brain death

Question 30

Outline the use of nerve and muscle biopsies

Answer 30

 may not provide definitive diagnosis and only indicate nature of pathological process
 mainly to differentiate between inflammatory or non-inflammatory (metabolic, degenerative)
 even in such cases it can guide treatment options
 preferably after electrodiagnostics

Question 31

Outline taking a nerve biopsy

Answer 31

 common peroneal nerve (cranial tibial m.)
 easily identified
 motor and sensory
 1/3 of width for about 1cm
 keep sample straight (but not stretched) in formalin or glutaraldehyde
 axon structure and density, myelin sheath thickness and integrity, Schwann cells, support tissues, infiltrates