CNS Flashcards
What are some abnormalities of the CNS
The most common disorders associated with the CNS are the inherited metabolic disorders which are often associated with mental retardation. Among these are the ff:
•Galactosaemia
•Hartnup disease
•Lesch-Nyhan syndrome
•PKU
•Wilson disease
The commonest findings in all these inherited diseases is often an enz. deficiency or defect which leads to the acclm of abnormal metabolites which affect normal mental function.
•Early screening and detection/diagnosis of these diseases are important for the institution of the appropriate treatment of these otherwise fatal conditions
•Other conditions can also give rise to mental disorders as a secondary consequence. These include COMA (whatever the cause),endocrine disorders e.g. Thyroid toxicosis, DKA, Cushings syndrome etc.
What are some endocrine disorders of the CNS
ENDOCRINE DISORDERS
•Diabetes-can affect CNS in a number of ways- DKA can result in hypoG, can also cause CNS acidosis and CNS hyperosmolality leading to an influx of fluid into the CNS-cerebral odema
•Adrenal Disease- inadequate release of cortisol can affect the brain and cause apathy, depression, fatique etc.
•Several metabolic associated derrangement- hypoglycaemia, hypoNa, hyperK, Hypotension can all add insult to the brain
•Xs glucocorticoids products and steroid assoc. can cause mood disturbances eg. Depression, delusion, hallucination etc.
•Thyroid Diseases- thyrotoxicosis and hypothyroidsm predictably affect the brain e.g. hypothyroid can cause mental retardation in children. Chronic thyroid insufficiency is associated with depression
What are some things you know about CSF specimen
CSF specimen is usually collected by lumbar puncture
•The CSF roughly resembles an ultrafiltrated plasma
• There are precautions and things to be noted during the collection of CSF and these include;
1.Pressure-the pressure employed should be recorded and specimen collected for bacteriological and biochemical tests.
2.Examination for cells, micro-organisms and protein are the basic investigations
3.In case flow of CSF proves inadequate, the little collected should be used for the above tests before considering any other tests
4.To avoid cross-contamination of specimen, different aliquots should be used for different tests
5.Since CSF is quite labile analysis should be done promptly
6. Specimen bottle should contain no preservative for CSF-protein but should contain fluoride oxalate for CSF-glucose. Why?
Physical Appearance: CSF is clear and colourless. Therefore any abnormal appearance should be noted at the time of collection
•If is turbid then it is likely to be due to leucocytes or some cases micro-organisms
•A clot is an indication of a possible high protein presence
•Blood traces is a strong indication of a probable or recent haemorrhage or damage to a vessel during puncture
•Xanthochromic(Yellow colour)appearance may be due to previous haemorrhage into the CSF and may also occur when CSF[Protein] is high. Patients with jaundice may also have yellow CSF-Why?
What is the total volume of the CSF in adults
The total volume of the CSF in adults is about 150ml (120ml-subarachnoid space, 30ml within the cerebral ventricles)
At what rate is CSF produced and reabsorbed
CSF is constantly produced and reabsorbed at the rate of only 500ml/day. This means that the total amount of CSF is replaced every 4-6hrs
•CSF re-absorption can occur along the entire neuro axis
•If absorption is impaired(as in meningeal inflammation, bact. Menin’s or sub. Haem’ge) CNS pressure and CSF volume both rise.
•An increased in the size of one component(brain, CSF, blood) leads to a sharp increase in pressure within the system unless there is a corresponding decrease in the volume of one of the other 2 components.
What is the composition of the CSF
The ionic and molecular composition of CSF differs from that of plasma for some components and is the same for others
•Changes in serum sodium are followed by corresponding >s in CSF Na. CSF Na(138-150mmol/L
•CSF potassium is however lower than plasma K(2.7-3.9mmol/L). CSF K is maintained within a very narrow conc. range in CSF despite wide fluctuations in plasma values
•Cl- and Mg are somewhat higher in CSF than in plasma. Cl-(116-127mmol/L) Mg. 24.4-30.5mg/L
•HCO-3 is somewhat lower
Describe CSF glucose (ranges, etc)
Normally ranges from 450-800mg/L
•Blood glucose equilibrate only after a long period of about 4hrs, so that CSF glucose at any given time reflects blood glucose levels during the past 4 hrs
•When a lumbar spinal puncture is performed and CSF glucose is determined a simultaneous sample of peripheral blood must also be drawn (esplly in the diagnosis of bacteria or carcinomatous meningitis
•LP and blood glucose shd be obtained only after patient has fasted for at least 4hrs
CSF glucose may be very low in patients with Hypoglycaemia and high in patients with hyperglycaemia.
•CSF glucose also may be low in patients with acute bacteria, cryptococcal or carcinomatous meningitis why?-(Due to consumption of glucose by leucocytes or other metabolising cells present in those disease conditions).
•How would CSF help in the differential diagnosis of patients with tubular meningitis or (viral) cerebral abscess as in viral meningitis or encephalitis?
Describe CSF proteins
Originate from serum and reach CSF space by pinocytosis across the capillary endothelium. Ref range-(0.1-0.4 g/L)
•Following electrophoretic separation ff; %
•Prealbumin-2-7%
•Albumin 56-76%, Low CSF albumin are found in ventricular and cisternal CSF. Raised levels are found in neonates
•Alpha-globulin 2-7%
•IgG 8-64mg/L
•IgA 0-0.2mg/L
•IgM 0-0.6mg/L
CSF protein may increase in various pathological conditions of the CNS and this includes:
1.Infection of the CNS e.g. Bacterial meningitis. Again in chronic or acute inflammatory conditions, CSF protein often increase due to increased capillary permeability.
2.In disease condition where there is likely to be demylination e.g. Alzheimer’s disease. Here CSF protein may increase in the range of 0.5-1.0g/L
3.Diseases that affect the brain or the meninges(cd be 10 or 20 neoplasms). Here the rise in CSF protein cd be due to a spinal block usually due to a tumour which interferes with the circulation of the CSF over the spinal cord. N.B. Specimen may appear xantochromic and a clot may form on standing.
Describe CSF IG
The CSF often contains small amount of the ff. immunoglobulins;
•IgG(8-64mg/L)
•IgA(Trace)
•IgM(Trace)
•Increases of CSF immunoglobulins esplly IgG may be due to increase ultra-filtration of plasma proteins including immunoglobulins into the CSF, or to increased local synthesis of these proteins.
•In diseases like Multiple sclerosis, Neurosyphilis and sub-acute Sclerosing Panencephalatis, there is always an increase in the local synthesis of IgG and in such conditions, the ratio of CSF IgG:CSF[Albumin] and again CSF[IgG]:CSF[T. Proten]are higher than normal.
•Precaution:CSF[IgG] measurement lacks specificity. There could be false +ves due to cross contamination.
What are some factors which affect CNS permeability
Inflammation-can increase the ease of entry of eg. Albumin, penicillin
•Toxins- e.g. Diodrast increase permeability
•Adrenal Steroids and Thyroid hormones- help to stabilize the integrity of blood-brain barrier
•Age- immature nervous system more permeable
•Mol. Wt- entry inversely prop. to size
•Protein Binding- highly protein-bound cmps enter CNS much less readily e.g. Phenytoin, Ca. Mg, Bil.
•Lipid Solubility- Cmds that are highly lipid soluble eg. CO , EOH, Neuroactive drugs readily enter the CNS
