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Central pontine myelinolysis
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==Prevention and Treatment== To minimise the risk of this condition developing from its most common cause, overly rapid reversal of hyponatremia, the hyponatremia should be corrected at a rate not exceeding 10 mmol/L/24 h or 0.5 mEq/L/h; or 18 mEq/L/48hrs; thus potentially avoiding demyelination<ref name="pmid24569125" /> although ODS can still occur with rises in osmolality within recommended ranges. No large clinical trials have been performed to examine the efficacy of therapeutic re-lowering of serum sodium, or other interventions sometimes advocated such as steroids or plasma exchange.<ref name="pmid24569125" /> Alcoholic patients should receive vitamin supplementation and a formal evaluation of their nutritional status.<ref>{{cite journal | vauthors = Kleinschmidt-DeMasters BK, Norenberg MD | title = Rapid correction of hyponatremia causes demyelination: relation to central pontine myelinolysis | journal = Science | volume = 211 | issue = 4486 | pages = 1068β1070 | date = March 1981 | pmid = 7466381 | doi = 10.1126/science.7466381 | bibcode = 1981Sci...211.1068K }}</ref><ref>{{cite journal | vauthors = Laureno R | title = Experimental pontine and extrapontine myelinolysis | journal = Transactions of the American Neurological Association | volume = 105 | pages = 354β358 | year = 1980 | pmid = 7348981 }}</ref> The effect of therapeutic saline, in particular hypertonic saline, is often implicated in rapid rises in serum Na and osmolality when treating patients with hyponatraemia. The effect of saline is twofold. There is an initial redistribution/dilution that rarely causes an unsafe rise in Na/osmolality. The rise in serum sodium due to redistribution alone can be estimated from the following equation. <math>\text{Na}_{\text{final}} = \frac{(\text{Na}_{\text{serum}} \times \text{ECF}) + (\text{Na}_{\text{infusate}} \times V_{\text{infusate}})}{\text{ECF} + V_{\text{infusate}}}</math> Where Na<sub>serum</sub> is the concentration of the patient's plasma sodium, ECF is an estimate of extracellular water in litres (approximately body weight in kg x 0.2 for males and body weight x 0.17 for females), Na<sub>infusate</sub> is the sodium concentration of the IV fluid and V<sub>infusate</sub> is the volume of the IV fluid in litres. For a 100kg man with a plasma Na of 105mmol/L given 300mLs of 2.7% saline (462mmol of Na) the final dilution of plasma sodium would only be 110mmol/L. <math>\frac{(105 \times 20) + (462 \times 0.3)}{20 + 0.3} = 110.3</math> This initial 5mmol/L rise is usually sufficient to stabilise the patient's acute neurological deterioration due to cerebral oedema. Note that it is a rise in osmolality that is the treatment aim rather than Na itself - however for simplicity the Na is used as a measure of the osmolality and the osmolar rise will be roughly twice the Na rise. Direct measurement of osmolality would be preferable but the turnaround time in most hospital laboratories is too long to be useful so serum Na is used and therapeutic targets are set against this. However after the initial rise from this mixing of 300mLs of 2.7% saline with the patients blood there is an osmotic load (Na<sup>+</sup> + Cl<sup>-</sup>) of 277mOsmol/kg available to the kidneys. With this load the patient could then potentially produce a water diuresis of up to 7L (277 / 40). 40mOsmol/Kg is approximately the most dilute the urine can be in humans. This secondary water diuresis (sometimes termed aquaresis) usually happens in the subsequent 24 hours in patients at risk - usually in patients initially suffering from a relative [[Syndrome of inappropriate antidiuretic hormone secretion|antidiuresis]] the cause of which has been reversed (such as urinary obstruction, medication side effects or [[potomania]]). Patients with an antidiuresis in which the cause persists (such as [[Small-cell carcinoma|small cell lung cancer]] or due to drug side effects that are long lasting or have not been stopped) are less prone to aquaresis. It is this secondary water diuresis that can cause a very rapid rise in serum sodium, sometimes greater then 2mmol/L/hr which can lead to ODS. Physicians treating patients at high risk of ODS should both measure plasma Na every 3-4 hours and also the urine output for at least 24 hours. If a brisk diuresis does occur (>2mL urine per kg body weight per hour) prophylactic [[desmopressin]] (4mg 8 hourly IV) can be given to limit free water clearance. If the patient does overshoot the recommended rise 5% dextrose in water can be given to bring the Na level back down to target levels. Once osmotic demyelination has begun, there is no cure or specific treatment. Care is mainly supportive. Alcoholics are usually given vitamins to correct for other deficiencies. The favourable factors contributing to the good outcome in central pontine myelinolysis without hyponatremia were: concurrent treatment of all electrolyte disturbances, early intensive care unit involvement at the advent of respiratory complications, early introduction of feeding including thiamine supplements with close monitoring of the electrolyte changes and input.<ref name="pmid21949915"/> Research has led to improved outcomes.<ref name="pmid11148672">{{cite journal | vauthors = Brown WD | title = Osmotic demyelination disorders: central pontine and extrapontine myelinolysis | journal = Current Opinion in Neurology | volume = 13 | issue = 6 | pages = 691β697 | date = December 2000 | pmid = 11148672 | doi = 10.1097/00019052-200012000-00014 | s2cid = 36063964 }}</ref> Animal studies suggest that [[inositol]] reduces the severity of osmotic demyelination syndrome if given before attempting to correct chronic [[hyponatraemia]].<ref>{{cite journal | vauthors = Silver SM, Schroeder BM, Sterns RH, Rojiani AM | title = Myoinositol administration improves survival and reduces myelinolysis after rapid correction of chronic hyponatremia in rats | journal = Journal of Neuropathology and Experimental Neurology | volume = 65 | issue = 1 | pages = 37β44 | date = January 2006 | pmid = 16410747 | doi = 10.1097/01.jnen.0000195938.02292.39 | doi-access = free }}</ref> Further study is required before using inositol in humans for this purpose.<ref>{{Cite web|title=INOSITOL: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews|url=https://www.webmd.com/vitamins/ai/ingredientmono-299/inositol|access-date=2021-10-14|website=www.webmd.com|language=en}}</ref>
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