Neurological Investigations Flashcards
Where is CSF produced?
Choroid plexus in the lateral ventricles (3rd & 4th ventricle)
Where does CSF circulate?
How much volume?
In the subarachnoid space and around the brain and spinal cord
125-150ml
Youve been asked to take a lumbar puncture.
At what level does the spinal cord end?
At what level should you take the LP?
What landmarks are you using to take it?
Spinal cord ends at L1/L2 in adults
LP is taken at L3/L4 or L4/L5.
Landmarks are
Tuffier’s line or intercrestal line between the two iliac crests. This line crosses the spine at L4/L5 (moreso L4)
ASIS at L4
What are the indications for an LP that are both diagnostic and therapeutic? (2)
Normal pressure hydrocephalus
Idiopathic Intracranial HTN
Give 6 diagnostic and 4 therapeutic indications for an LP
Diagnostic:
CNS infection
SAH - Xanthochromia
CNS vasculitis
MS - Multiple sclerosis
GBS (Guillian Barre)
Paraneoplastic syndrome
Therapeutic:
Intrathecal chemo
spinal anaesthesia
Both: Normal pressure hydrocephalus
Idiopathic Intracranial HTN
Give 4 contraindications for taking an LP
1) Raised ICP
2) Coagulopathy/bleeding diathesis (thrombocytopenia, coag deficiency, anti-coag use)
3) Suspected spinal epidural abscess
4) infection at puncture site (cellulitis)
A patient has suspected raised ICP and your consultant has asked you to take an LP if possible. How will you check?
Fundoscopy - Papilloedema
CT - midline shift, space occupying lesion, intracranial haemorrhage
Xanthochromia can appear in 2 scenarios. What are they?
SAH
Guillian Barre
What are the components of CSF analysis?
Appearance
RCC
WCC
Protein
Glucose
Presence of organisms (gram stain and culture)
CSF is typically clear, colourless, and almost acellular. What is the expected appearance of the CSF in the following scenarios:
Bacterial meningitis:
TB meningitis:
SAH:
Traumatic tap:
Viral meningitis:
Multiple Sclerosis:
Guillian-Barre:
Bacterial meningitis: Can be clear, cloudy, turbid or purulant => many possible
TB meningitis: often very cloudy, but can be clear
SAH: Yellow/pink discolouration (xanthochromia)
Traumatic tap: blood-stained
Viral meningitis: clear
Multiple Sclerosis: clear
Guillian-Barre: usually clear, but xanthochromia if very elevated protein
CSF is typically clear, colourless, and almost acellular. Do you expect to see raised WCC in the following scenarios? If so, indicate the predominant cell type
Bacterial meningitis:
TB meningitis:
Viral meningitis:
Fungal CNS infection:
Multiple Sclerosis:
Guillian-Barre:
SAH:
Bacterial meningitis: Yes - PMN
TB meningitis: Yes - PMN early, Lymphocytes late
Viral meningitis: Yes - Lymphocytes
Fungal CNS infection: Yes - Lymphocytes
Multiple Sclerosis: Maybe - Lymphocytes
Guillian-Barre: No
SAH: Yes - >1:1000RBC + occasional eosinophilia
How would you expect the glucose and protein levels to be in the following scenarios:
Bacterial meningitis:
TB meningitis:
Viral meningitis:
Fungal CNS infection:
Multiple Sclerosis:
Guillian-Barre:
SAH:
Abscess:
Malignancy:
Bacterial meningitis: low glucose very high protein
TB meningitis: low glucose, high protein
Viral meningitis: Normal glucose, normal protein
Fungal CNS infection: low glucose, high protein
Multiple Sclerosis: normal glucose, high protein
Guillian-Barre: normal glucose, high protein
SAH: low glucose, high protein
Abscess: normal glucose, high protein
Malignancy: normal glucose, high protein
CSF results come back showing oligoclonal bands. What are your ddx?
SAH
Guillian barre syndrome
MS
CNS lymphoma
Lyme disease
Neurosarcoid
You suspect meningitis. What will you send the CSF for?
Microscopy
Culture/PCR
Gram stain
You are performing an LP and notice it is kind of red. What are your top 3 ddx
Traumatic tap
SAH
Guillian barre
A 19 year old student presents to the emergency department with a 1 day history of headache, photophobia and fevers. Neurological exam
reveals no signs of focal neurology and there are no signs of raised intracranial pressure. A lumbar puncture is carried out which reveals the
following. Serum glucose is 6mmol/L.
What is the most likely diagnosis?
What additional investigations should be performed on CSF?
Bacterial Meningitis
CSF culture
A 29 year old man presents to the emergency department at 9pm with a 1 hour history of a sudden onset severe occipital headache. He has
some mild neck stiffness on examination. CT Brain reveals no acute abnormalities. The following morning he undergoes a lumbar puncture. Serum glucose is 6 mmol/L.
What was the most likely diagnosis?
Why were 3 samples taken?
SAH
To ensure it wasnt a traumatic LP
A 29 year old man presents to the emergency department at 9pm with a 1 day history of a headache. He complains of generalised myalgia
and chills. CT Brain reveals no acute abnormalities. A lumbar puncture is performed. Routine bloods show mildly elevated white cell count with lymphopaenia, with mildly elevated CRP. Serum glucose is 6 mmol/L.
What is the most likely diagnosis?
Traumatic LP
You can see that as more samples were taken, the results varied significantly
A 32 year old woman presents to the emergency department. She has a 1 day history of gradual onset left upper limb weakness. She also reports an episode of painful blurred vision three months ago which resolved fully. Examination reveals reduced power and brisk reflexes in her left upper limb. Serum glucose is 6 mmol.
What is the most likely diagnosis?
What additional testing on the CSF will confirm the diagnosis?
What other tests should be performed to confirm the diagnosis?
Multiple sclerosis (active)
CSF analysis for oligoclonal bands
MRI brain looking for while demyelinated plaques
A 46 year old man is brought to the emergency department. He has been complaining of headaches and fevers for several days, and became more unwell today with vomiting and confusion. He has
been living in a homeless shelter for several months, has a known diagnosis of HIV and has been non-compliant with his anti-retroviral medication. Temperature is 38.2 degrees Celsius, GCS is 13/15 and there is photophobia on examination. Serum glucose is 6 mmol/L.
What is the most likely diagnosis?
What additional testing should be performed on the CSF to confirm the diagnosis?
Cryptococcal meningitis (HIV made him susceptible to it)
Cryptococcal antigen test or CSF PCR. Also must rule out TB which is also a possibility in an immunocompromised patient => Acid-fast bacilli stain and culture
One of the main indications of an EMG is to determine if an abnormality is neurogenic or myopathic. Explain with 3 differences
1) Electrical activity at rest: Myopathy has little to no spontaneous electrical activity whereas neurogenic abnormalities have spontaneous discharge with fibrillations and fasciculations. This is increased with needle insertion
2) Motor unit potential: Myopathy typically has low amplitude and shortened motor unit potentials whereas neuropathic have large amplitude and prolonged action potential
3) Interference pattern on EMG: Myopathies have full interference pattern with high frequency but low amplitude. Neuropathic ones have reduced interference => low frequency but large amplitude
