CPATH Flashcards
Jason is a 4 y/o who complains of a worsening headache over the course of 2 days. His mother had been treating him with pain syrup but started worrying when he developed a fever, refused to eat and wanted to sleep all the time. She took him to Red Cross Hospital where the paediatrician found that Jason had neck stiffness and signs of raised intracranial pressure. He immediately suspected meningitis and started Jason on antibiotics. Blood cultures and further tests were done to identify the causative organism.
Describe the cerebrospinal fluid (CSF) findings if one had been done, given that bacterial meningitis is suspected (2)
Appearance turbid, Glucose, Protein, White cells raised neutrophils
State the most common endocrine disorder complicating meningococcal meningitis (1)
Adrenal failure (Waterhouse-Friederichson syndrome) (1)
Describe how you would suspect this disorder (Q.26) clinically, and how you would confirm it biochemically (2½)
- Profound shock/ circulatory collapse (1)
- Hypoglycaemia, hyperkalaemia, hyponatraemia, acidosis (1 ½) (also accept low cortisol, low aldosterone, high renin)
A patient in the medical ward has been diagnosed with bacterial meningitis. His blood glucose is found to be 10mmol/l. What approximate value would you expect his CSF glucose to be: (2)
A: before treatment is initiated?
B: after full recovery? (Assuming his blood glucose remains at 10mmol/l)
Less than 6 mmol/l or less than 60% of blood glucose (1)
6-8mmol/l or 60-80% blood glucose (1)
Name two biochemical tests commonly performed on CSF when meningitis is suspected and state how the results change in bacterial meningitis (2)
Glucose (goes down, often to zero), Protein (increases many fold)
Briefly explain why CSF chloride levels are typically lower in patients with tuberculous meningitis (1)
In TBM, protein levels in CSF increase dramatically and chloride levels therefore decrease to maintain electroneutrality.
List of diagnoses: SAH (Subarachnoid haemorrhage), Multiple Sclerosis, Normal CSF, TB meningitis, Viral meningitis, Fungal meningitis, Bacterial meningitis, Hypoglycaemia
A: Low chloride, ++ protein, glucose
B: Xanthochromia
C: Oligoclonal banding
A: TB meningitis (1)
B: SAH (1)
C: Multiple Sclerosis (1)
Briefly explain why the CSF glucose needs to be interpreted with a plasma glucose measurement (2)
CSF glucose is in equilibrium with blood glucose concentration [1] over the past 4 hours [½]; interpretation therefore requires knowledge of concurrent blood glucose [½].
Name one test used to evaluate blood-brain barrier permeability [1]
CSF:plasma albumin ratio; or IgG index
List four (4) biochemical abnormalities that occur in tumour lysis syndrome [2]
Hyperphosphataemia, Hyperkalaemia, Hyperuricaemia, Hypocalaemia, Metabolic acidosis
Chloride concentration in cerebrospinal fluid (CSF) is normally higher than in plasma. Outline the reason for this (2)
CSF has a much lower negatively charged protein content than plasma, so to maintain electroneutrality, chloride increases.
State why the CSF protein concentration is higher in the lumbar region than in the ventricles (2)
Due to higher hydrostatic pressures lower down in the subarachnoid space, water is forced out into the intersttitial space until the colloid osmotic pressure (and protein concentration) of the CSF increases to a point that an equilibrium is reached. Lower down, CSF circulation is slower, allowing more time for equilibration with plasma proteins
Define the IgG index (1)
IgG index = (IgGCSF/ AlbuminCSF)/(IgGserum/Albuminserum)
State what a raised IgG index implies (1)
Increased local (intrathecal) production of IgG
List two (2) causes of a raised IgG index (1)
Neurosyphilis, multiple sclerosis
In a patient with a raised total CSF protein, state the significance of an increased IgG/albumin ratio in CSF, particularly if this ratio in plasma is normal (2)
Local IgG production due to an infective or autoimmune process within the CNS, rather than a non-specific increase in blood-brain barrier permeability.
Indicate the significance of a very high (rather than low) CSF glucose in a comatose patient (1)
Reason for the coma is uncontrolled diabetes rather than meningitis.
In a patient with a high total CSF protein, describe how you would distinguish increased protein permeability of the blood/brain barrier from antibody production within the CNS (such as may occur in neurosyphilis or multiple sclerosis) (2)
By examining the ratio of CSF IgG to albumin, or ideally, by dividing the CSF IgG/albumin ratio by the serum IgG/albumin ratio. The value for increased permeability is <0.7, while for local IgG production it is >0.7.
Name two (2) causes for a bloodstained CSF, and suggest two (2) ways by which they can be differentiated, explaining how the responses differ in each case (6)
Subarachnoid haemorrhage (SA), bloody tap (BT). By collecting sequential samples (clears in BT, remains uniformly bloodstained in SA). By spinning down and observing supernatant (clear in BT, possibly xanthochromic in SA).
Explain why chloride is normally higher in CSF than in serum (2)
Molar concentration of protein is much lower in CSF than in serum. To maintain electroneutrality chloride (negatively charged) is higher.
List two (2) analytes that are used to determine blood brain barrier permeability (1)
Albumin and Immunoglobulin
Name a chemical analyte measured in CSF (not provided in this case) which can be useful in the diagnosis of bacterial meningitis (½)
Lactate
List three (3) causes for a massively elevated CSF protein (e.g. 10g/L) (1½)
Obstruction of CSF flow in the spine (Froin Syndrome): Tumour, Abscess, Disc prolapse
Explain how Froin’s syndrome (spinal block) can affect CSF protein levels (2)
Failure of CSF to circulate extends its residence time and allows time for proteins to leak across from blood into CSF. This can result in extremely high CSF protein concentration
