Neurological investigations

Question 1

What are the 2 commonly performed types of MRI scan?

Answer 1

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.

Question 2

What is myelography and how is it performed?

Answer 2

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.

Question 3

What is angiography used for and how is it done?

Answer 3

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.

Question 4

How do you visualise the venous system with angiography?

Answer 4

Delayed x-rays allow visualisation of the venous system.

Question 5

What is an electroencephalogram (EEG)?

Answer 5

It records the electrical activity of the brain. Its major use is in the diagnosis and characterisation of epilepsy.

Question 6

What is the normal background rhythm in EEG and where is it best measured?

Answer 6

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.

Question 7

What do focal, slow waves suggest in EEG?

Answer 7

May represent focal structural lesions (tumour, infarct etc.) and a brain scan is normally indicated.

Question 8

What do widespread, slow waves suggest in EEG?

Answer 8

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.

Question 9

What do paroxysmal spikes and sharp waves on EEG suggest? What do they represent?

Answer 9

They suggest epilepsy.

Represent the brief, near simultaneous discharges of large numbers of neurones.

Question 10

How can you tell the difference between focal and generalised epilepsy on EEG?

Answer 10

The spikes and waves will be focal in focal epilepsy and generalised in generalised epilepsy.

Question 11

What is the difference between an interictal EEG and an ictal EEG? What can be diagnosed in one but not the other?

Answer 11

Interictal EEG = recorded between seizures
Ictal EEG = recorded during a seizure
Epilepsy can be diagnosed in ictal EEG but not interictal.

Question 12

What does a seizure seen on EEG look like?

Answer 12

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.

Question 13

What 2 functions of nerves do nerve conduction studies check?

Answer 13

Sensory and motor conduction.

Question 14

What abnormalities are detected by nerve conduction studies?

Answer 14

Slowing due to demyelination

Reduction in amplitude of response due to loss of axons.

Question 15

How are nerve conduction studies done?

Answer 15

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.

Question 16

What is electromyography?

Answer 16

Electrical activity of muscles by inserting a fine concentric needle into the muscle to allow the study of muscle function.

Question 17

How is lumbar puncture done?

Answer 17

1. 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.
2. Find the anterior superior iliac spine; vertically beneath this is the L3-4 interspace.
3. Sterilise the skin (iodine)
4. Inject lidocaine subcut and anaesthetise deeper tissues.
5. Insert needle, pointing towards the umbilicus.
6. 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.

Question 18

When might excess leukocytes be present in CSF?

Answer 18

Infection, malignancy, and inflammatory conditions such as sarcoidosis.

Question 19

When is a higher neutrophil count present in CSF?

Answer 19

Usually due to acute bacterial meningitis.

Question 20

When are excess mononuclear cells seen in CSF?

Answer 20

With chronic meningitis (tuberculous or fungal), viral meningoencephalitis, partially treated bacterial meningitis chronic inflammation and malignant meningeal infiltration.

Question 21

What confirms a subarachnoid haemorrhage? What suggests it? Why else could this be present?

Answer 21

Xanthochromia confirms SAH.

RBC are seen in SAH, but could also be due to a traumatic tap.

Question 22

If glucose is being measured in CSF what else is measured?

Answer 22

Blood glucose because CSF glucose should be around 60% of it.

Question 23

When is CSF glucose reduced and by how much is it reduced?

Answer 23

Profoundly reduced in acute bacterial meningitis and tuberculous meningitis (<1mmol/l)
Milder reductions suggest viral infections, malignant meningitis and inflammatory conditions.

Question 24

When is a rise in CSF protein without a rise in CSF cellularity seen?

Answer 24

In inflammatory neuropathies. Especially Guillian-Barre syndrome.

Question 25

What do oligoclonal bands in serum and CSF suggest?

Answer 25

Oligoclonal bands in both serum and CSF suggest systemic infection, autoimmune disease, sarcoidosis or neoplasia.
Oligoclonal bands only in CSF (local CNS synthesis) suggests local CNS disease - especially multiple sclerosis, but sometimes CNS inflammation, neoplasm or infection.

Question 26

What are oligoclonal bands?

Answer 26

Visible as an increased concentration of restricted bands of IgG after isoelectric focusing and immunofixation of IgG.

Question 27

What else should you consider taking with lumbar puncture CSF?

Answer 27

Serum sample

Blood glucose

Question 28

What is the difference between a bloody tap and a traumatic tap? How can you tell them apart?

Answer 28

Traumatic tap is when there is a cannulation of the venous plexus during lumbar puncture. When you take successive bottles of CSF, the red cell count falls as the proportion of CSF increases.
Bloody tao is when there is a SAH and the CSF is uniformly blood stained in all bottles. Haemoglobin breakdown products (xanthachromia) appear after 12 hours.

Question 29

Why is a blood tap useful?

Answer 29

Because it shows SAH without needing to wait 12 hours for xanthachromia (haemoglobin breakdown product).

Question 30

What is the commonest complication of lumbar puncture? What causes it?

Answer 30

A headache.
This is due to reduced CSF pressure from CSF leaking after the procedure - it is made worse on sitting and standing because this reduces intracranial pressure.

Question 31

What are the contraindications for lumbar puncture?

Answer 31

1. Focal symptoms or signs attributable to intracranial disease
2. Symptoms of raised intracranial pressure including confusion
3. Papilloedema (may be absent in raised intracranial pressure)
4. Neuroimaging evidence of obstruction to CSF flow
5. Bleeding diathesis
6. Local sepsis e.g. sacral sores

(in some situations LP may be deemed as safe after neuroimaging has excluded obstruction to CSF flow).