Diagnostic tests Flashcards
What blood testing can be performed?
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
What immune mediated dzs can be tested for?
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)
What tests give you a quick indication of if a pet has myasthenia gravis?
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
What serological testing may be required?
Dogs - Neospora Toxoplasma CDV Cryptococcus Tick-borne diseases…
Cats FIV FeLV FIP Toxoplasma Cryptococcus
Outline the assessment of CSF analysis
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
When is CSF analysis contraindicated
↑ICP: mental status pupil size and PLR abnormal postures vestibular eye movement
clotting problems
Chiari-like malformation
AA instability or trauma
What do you analyse in CSF?
differential cell count cytology protein PCRs normal: ≤ 5 WBC/µl no RBC protein ≤ 30-45 mg/dl-
Outline cervical CSF collection
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
Outline lumbar CSF collection
lumbar subarachnoid space
lateral recumbency
L5-L6 in dogs & L6-L7 in cats (and small dogs)
2.5-3.5 inch needle, 21-22G
When may you see a neutrophilic pleocytosis on CSF?
SRMA bacterial (intracellular) MUOs fungal FIP post myelography, haemorrhage, trauma, neoplasia
When may you see a mononuclear pleocytosis
MUOs
CNS lymphoma
viral (CDV)
bacterial and SRMA (chronic)
When may you see a mixed pleocytosis?
MUOs bacterial and SRMA (chronic) fungal protozoal non-inflammatory dx (infarction)
When may ultrasound be useful?
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…
When may you see eosinophilic pleocytosis
eosinophilic ME
fungal
protozoal
parasitic
What anomalous ddx are rads good for seeing?
AA luxation
transitional vertebrae
abnormal no. of vertebrae
hemivertebrae, block vertebrae, butterfly vertebrae
How can rads be used to check for trauma
Can see fractures and luxations
orthogonal views, survey of all spine, chest and abdomen
3 compartment model
Where can myelography detect issues
extradural
intradural (extramedullary vs intramedullary)
Outline the use of myelography
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)
Outline the use of CT
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)
Outline the use of brain CT
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)
When is CT of the spine useful?
mainly used to help interpret myelography
when this is difficult to interpret (swollen SC)
some congenital/developmental abnormalities
trauma
What is the use of MRI?
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
What are the different MRI sequences?
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)
What is the use of electrodiagnostics?
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
Outline electromyography
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
Outline nerve conduction velocities
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)
Outline F wave assessment
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
Outline repetitive nerve stimulation
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
Outline the BAER
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
Outline the use of nerve and muscle biopsies
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
Outline taking a nerve biopsy
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
