Neurological investigations Flashcards
What are the 2 commonly performed types of MRI scan?
T1 - water is dark and anatomical resolution is optimised
T2 - water is bright and pathological tissue is often highlighted, but with some loss of anatomical resolution.
What is myelography and how is it performed?
Myelography is used for imaging the spinal cord and roots in centres where MRI is not available or if it is contraindicated.
A lumbar puncture is performed and water-soluble contrast medium is introduced into the CSF.
What is angiography used for and how is it done?
It is the gold standard test for imaging blood vessels intracranially in the neck.
A canula is inserted into the femoral artery under local anaesthetic, manoeuvred into the aortic arch and into the carotid or vertebral arteries. Contrast is injected and x-rays are taken. Delayed x-rays allow visualisation of the venous system.
How do you visualise the venous system with angiography?
Delayed x-rays allow visualisation of the venous system.
What is an electroencephalogram (EEG)?
It records the electrical activity of the brain. Its major use is in the diagnosis and characterisation of epilepsy.
What is the normal background rhythm in EEG and where is it best measured?
Normal background rhythm in waking adults is 8-13Hz alpha activity. This is best seen over the occipital cortex when the patient’s eyes are shut.
What do focal, slow waves suggest in EEG?
May represent focal structural lesions (tumour, infarct etc.) and a brain scan is normally indicated.
What do widespread, slow waves suggest in EEG?
Diffuse encephalopathic processes, often due to metabolic disturbances such as renal/hepatic failure, drug intoxication, encephalitis, advanced degenerative processes or sometimes thalamic or brain stem lesions that affect arousal.
What do paroxysmal spikes and sharp waves on EEG suggest? What do they represent?
They suggest epilepsy.
Represent the brief, near simultaneous discharges of large numbers of neurones.
How can you tell the difference between focal and generalised epilepsy on EEG?
The spikes and waves will be focal in focal epilepsy and generalised in generalised epilepsy.
What is the difference between an interictal EEG and an ictal EEG? What can be diagnosed in one but not the other?
Interictal EEG = recorded between seizures
Ictal EEG = recorded during a seizure
Epilepsy can be diagnosed in ictal EEG but not interictal.
What does a seizure seen on EEG look like?
The EEG appearance of a focal seizure is characterised by an evolving seizure discharge. Normal rhythms are replaced by rhythmic activity which may be spiky, slow or fast but increases in prominence during the ictus and then subsides, to be replaced by slow activity, for minutes to hours until the EEG returns to its normal interictal appearance.
What 2 functions of nerves do nerve conduction studies check?
Sensory and motor conduction.
What abnormalities are detected by nerve conduction studies?
Slowing due to demyelination
Reduction in amplitude of response due to loss of axons.
How are nerve conduction studies done?
A nerve is stimulated at one point along it, and recording a distant sight along the nerve/a muscular response. By knowing the distance in between the 2 sites allows you to measure the speed of the action potential and the amplitude response of the muscle.
What is electromyography?
Electrical activity of muscles by inserting a fine concentric needle into the muscle to allow the study of muscle function.
How is lumbar puncture done?
- Patient is in the left lateral position, curled up as much as possible, with the knees separated by a pillow. Ensure the right shoulder remains exactly above the left shoulder and place a single pillow under the patient’s head. This is all done to ensure the spine is straight.
- Find the anterior superior iliac spine; vertically beneath this is the L3-4 interspace.
- Sterilise the skin (iodine)
- Inject lidocaine subcut and anaesthetise deeper tissues.
- Insert needle, pointing towards the umbilicus.
- The first dense resistance is the supraspinous ligament (1cm in). The second is interspinous ligament (3-5cm in) and then next is the dura - once through there should be a back flow of CSF when the stylet is removed.
When might excess leukocytes be present in CSF?
Infection, malignancy, and inflammatory conditions such as sarcoidosis.
When is a higher neutrophil count present in CSF?
Usually due to acute bacterial meningitis.
When are excess mononuclear cells seen in CSF?
With chronic meningitis (tuberculous or fungal), viral meningoencephalitis, partially treated bacterial meningitis chronic inflammation and malignant meningeal infiltration.
What confirms a subarachnoid haemorrhage? What suggests it? Why else could this be present?
Xanthochromia confirms SAH.
RBC are seen in SAH, but could also be due to a traumatic tap.
If glucose is being measured in CSF what else is measured?
Blood glucose because CSF glucose should be around 60% of it.
When is CSF glucose reduced and by how much is it reduced?
Profoundly reduced in acute bacterial meningitis and tuberculous meningitis (<1mmol/l)
Milder reductions suggest viral infections, malignant meningitis and inflammatory conditions.
When is a rise in CSF protein without a rise in CSF cellularity seen?
In inflammatory neuropathies. Especially Guillian-Barre syndrome.
