CENTRAL PONTINE AND EXTRA- PONTINE MYELINOLYSIS: THE OSMOTIC DEMYELINATION SYNDROMES

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1 iii22 Correspondene to: Dr R J Martin, Department of Neurology, Glouestershire Royal Hospital, Great Western Road, Glouester GL1 3NN, UK; roswell.martin@glour-tr. swest.nhs.uk CENTRAL PONTINE AND EXTRA- PONTINE MYELINOLYSIS: THE OSMOTIC DEMYELINATION SYNDROMES OSMOTIC C RJMartin J Neurol Neurosurg Psyhiatry 2004; 75(Suppl III):iii22 iii28. doi: /jnnp entral pontine myelinolysis (CPM) was desribed by Adams and olleagues in 1959 as a disease affeting aloholis and the malnourished. 1 The onept was extended from 1962 with the reognition that lesions an our outside the pons, so-alled extrapontine myelinolysis (EPM). In 1976 a link between these disorders and the rapid orretion of sodium in hyponatraemi patients was suggested, and by 1982 substantially established. In this review we disuss the linial, pathologial, and aetiologial features of the disease, the dilemma faing liniians treating patients with severe hyponatraemia, and treatment opportunities. DEMYELINATION SYNDROMES: CPM AND EPM Clinial manifestations Central pontine myelinolysis (CPM) Nothing has been added to the linial desription of CPM sine the original report. The patient has usually gone through a biphasi linial ourse, initially enephalopathi or presenting with seizures from hyponatraemia, then reovering rapidly as normonatraemia is restored, only to deteriorate several days later. The initial signs of the CPM, whih reflet this seond phase, inlude dysarthria and dysphagia (seondary to ortiobulbar fibre involvement), a flaid quadriparesis (from ortiospinal trat involvement) whih later beomes spasti, all from involvement of the basis pontis (fig 1); if the lesion extends into the tegmentum of the pons pupillary, oulomotor abnormalities may our. There may be an apparent hange in onsious level refleting the loked-in syndrome that a large lesion in this site is partiularly liable to produe. If lesions of EPM are also present the linial piture may be very onfusing, as added to the above, or even preeding, an be a variety of apparently psyhiatri and behavioural hanges and movement disorders (outlined below). To summarise: whenever a patient who is gravely ill with aloholism and malnutrition or a systemi medial disease develops onfusion, quadriplegia, pseudobulbar palsy, and pseudo oma ( loked-in syndrome ) over a period of several days, one is justified in making a diagnosis of entral pontine myelinolysis. 2 Extrapontine myelinolysis (EPM) The pathologial hanges are idential to those of CPM. Studies show that lesions an our with or without CPM: in a neropsy series of 58 ases isolated CPM was present in about half, CPM with EPM in about three fifths, and isolated EPM in about two fifths of ases (fig 2). 3 A variety of sites may be involved (table 1). The lesions are often strikingly symmetrial. The age of lesions in the various sites in EPM is ontemporaneous. CPM and EPM are the same disease, sharing the same pathology, assoiations, and time ourse but differing in linial manifestations. Movement disorders in EPM While no signifiant advane on the desription of the linial features of CPM has been made sine the original report, the manifestations of EPM ontinue to attrat publiation, espeially in the movement disorder literature. This is a onsequene of the widespread nature of suh lesions. Mutism, parkinsonism, dystonia, and atatonia have all been desribed. Catatonia has been reported on a ouple of oasions, one as a brief episode lasting days before resolving and being replaed with parkinsonian features, and one following the resolution of spasti tetraparesis, itself settling spontaneously over two weeks. However, this manifestation may be underreognised. In EPM a variety of linial features an be seen to evolve for example, a patient who progressed from spasti paraparesis with postural limb tremor and myoloni jerks to a parkinsonian piture with horeoathetosis, and finally into a permanent parkinsonian state with dystonia. In another ase parkinsonism dominated the linial piture with signs of pyramidal dysfuntion. These then resolved over four months, being replaed by transient retroollis and oromandibular dystonia and a permanent foal dystonia of the arm with spasmodi dysphonia. J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

2 NEUROLOGY IN PRACTICE Figure 1 A reminder of the anatomy of the pons; although inluded to larify the anatomial terms, a small lesion is in fat present, illustrating how easily suh lesions may be missed on ursory pathologial examination. The movement disorders of EPM represent a treatable manifestation of the osmoti demyelination syndrome in that a rewarding symptomati improvement an our with dopaminergi treatment in those with parkinsonian features. Other osmoti demyelination lesions Other neurologial lesions have been linked to CPM and EPM inluding erebral ortial slerosis and involvement of the posterior olumns. Interestingly lesions in these regions were desribed in the original reports of CPM/EPM. Clinial senarios of CPM/EPM Although initially desribed as ourring in aloholis (three out of four of Adams original patients) and the undernourished, CPM/EPM has also been reported in adults with a variety of serious illnesses and after ertain surgial proedures and even in toddlers with psyhogeni polydipsia (table 2). It very rarely ours in the absene of another signifiant illness. Hyponatraemia is the most ommon biohemial abnormality in mediine, yet despite this CPM/ EPM is seen in a fairly restrited number of linial situations, and is unommon in some disorders where similar large osmolality shifts our. The assoiation with aloholism was the first to be noted and ontinues to be partiularly frequent (in up to 40% of ases). The original authors pointed out pathologial similarities to Marhiafava-Bignami disease (demyelination of the orpus allosum and other ommissural fibre systems), a reognised ompliation of aloholism. Wernike s is a not infrequent aompaniment (30% in pathologial series). Some point out that alohol itself interferes with sodium/ water regulation by suppression of antidiureti hormone (ADH), and inadequate nutrition of aloholis is an obvious aompaniment. CPM is a reognised ompliation of liver transplantation. In a 10 year retrospetive series of 627 transplants it ourred in 2% of ases (but ontributed only a tiny proportion to the overall neurologial ompliation rate of 26%); it was oneded that this was likely to be an underestimate, the authors appreiating that postmortem studies showed a higher inidene. The possibility of EPM aounting for a proportion of the aute enephalopathy, the largest neurologial ompliation following liver transplantation, does not appear to have been investigated. Table 1 Lesions of entral pontine myelinolysis (CPM) and extrapontine myelinolysis (EPM) (in desending order of frequeny) 3 Pons Cerebellum Lateral geniulate body External apsule Extreme apsule Hippoampus Putamen Cerebral ortex/subortex Thalamus Caudate nuleus The following 10% or less: Claustrum Internal apsule Midbrain Internal medullary lamella Mamillary body Medulla oblongata CPM 1/2 CPM+ EPM 3/5 EPM 2/5 Figure 2 Relative proportions of entral pontine myelinolysis (CPM), extrapontine myelinolysis (EPM), and CPM with EPM. Osmoti demyelination, however, does not seem to our with anything like the frequeny one would expet in renal dialysis. It is thought that urea is ating in the renal failure patients as an ineffetive solute that is, it ontributes to measured osmolality but as it easily rosses ell membranes does not ontribute to toniity, thus proteting from the rapid shifts in sodium whih an our in haemodialysis. Animal work suggests the mehanism may be more omplex. Table 2 Disease states assoiated with CPM/EPM, often more than one assoiation present Aloholism (ommon) Malnutrition (ommon) After prolonged diureti use (frequent) Psyhogeni polydipsia (rare if aute) Burns (infrequent, and often in ontext of hypernatraemia) Post-liver transplant (well reognised) Post-pituitary surgery (rare) Post-urologial surgery/gynaeologial surgery, espeially if involving glyine infusions (rare) iii23 J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

3 iii24 It is similarly very rare in diabetes, despite the pronouned shifts in osmolality that our. Only a handful of ases exist in the literature (9 of 757 ases in a review of ases published before 2002). Pathology The pons is divided anteroposteriorly into the basis pontis and the tegmentum. CPM, unless very severe, is predominantly a lesion of the basis pontis, sparing the tegmentum (figs 1 and 3). The original authors argued that the pathologial proess started in the entral pons near the median raphe and that it spread out like a brush fire into the surrounding basis pontis. The lesion may extend up to the midbrain, but only very rarely down to the medulla. At its greatest extent it is onfined in three dimensions to two pyramids side by side, their bases at the origin of the trigeminal nerve. Intriguing is the lesion shape and loation. Its entre appears loalised at a point equidistant from the CSF spaes around the brainstem. The loalisation of the lesion within this region of the pons has long been one of the most puzzling aspets of the ondition. One hypothesis rests on the fat that this is a region of maximal admixture of grey and white matter elements, whih examination of any brain atlas stained for myelin will onfirm. In support of this the lesions of EPM similarly seem to be in similar regions of grey white apposition. The striking appearane of the lesion, whih ould not, it was argued, have been missed by earlier pathologists, lent support to the view that some new aetiologial fator was at work from the 1950s onwards. Ultimately it was to be realised that this was a onsequene of the plasti revolution and the widespread introdution of intravenous fluid therapy at that time. Mirosopially the lesion shows degeneration and loss of oligodendroytes with preservation of axons unless the lesion is very advaned. This author annot see the value in hanging the terminology of these onditions from the desriptive entral pontine myelinolysis and extra-pontine myelinolysis to the vaguer osmoti demyelination syndromes. The original authors Adams, Vitor, and Manall 1 oined the term entral pontine myelinolysis after areful thought. The loation of Figure 3 Pons with myelin stain (Luxol fast blue) showing lesion in basis pontis (CPM). Different ase from gross speimen in fig 1. NEUROLOGY IN PRACTICE the prinipal lesion is given, from whih the neurologial onsequenes of the lesion an be dedued. I suspet that more than one the visualisation of a lesion in the entre of the pons has triggered reognition of CPM by a linial team. The term demyelination was deliberately avoided in order to distinguish this ondition in whih the myelin loss ours without any obvious inflammatory infiltrate from the inflammatory nature of multiple slerosis. Aetiology of CPM/EPM Adams and olleagues 1 argued that as the lesions were both symmetrial and onstant in loation, both of whih are hallmarks of toxi or metaboli diseases, the aetiology was fundamentally biohemial. They were unable to appreiate the role of sodium (Na + ) beause when these patients were olleted (over 10 years in the 1950s) the measurement of serum eletrolytes was not routine in linial management. The only eletrolyte disturbane they noted in their original paper was hypokalaemia, deteted in one patient as a onsequene of a hange in the ECG. Tomlinson in 1976 is generally redited with the suggestion that the rapidity of orretion of Na + was the aetiologial fator. This was followed up by the animal work of Laureno (in dogs) and Kleinshmidt-DeMasters and Norenberg (in rats) who showed onviningly that the rate of orretion was the key ausative fator. 4 The lesions in dogs are virtually idential to those of human ases and the linial ourse and manifestations are idential. The animal work is so onvining that one an regard the aetiologial fator to be beyond doubt. To understand how it happens we need to understand what happens in hyponatraemia. Physiologial hanges in hyponatraemia and its orretion As water flows freely aross the blood brain barrier and ell membranes a fall in serum sodium (in the absene of a ompensatory rise in other osmoles) will ause entry of water into brain ells and onsequent brain swelling. Protetive mehanisms ome into play during the development of serum hypotoniity in all ell types to maintain ell volume, a proess termed regulatory volume derease. In the brain the first protetive mehanism to at preedes this and is the foring of interstitial sodium-rih fluid into erebrospinal fluid (CSF) as a result of hydrostati pressure. 5 6 In the rat this ours within minutes. Over the next few hours potassium is lost, and this is maximal after 24 hours. The maximum ation loss that ours is 18% but this would put a theoretial limit on survivable hyponatraemia at 103 mmol/l if the loss of inorgani ions were the only available mehanism, and rats, like man an survive Na + onentrations below this. It was realised that other solutes ontribute and these are organi osmoles (suh as myoinisotol, taurine, and glutamate) whih are lost over a day to a very few days, rendering the ell isotoni to the extraellular fluid and maintaining ell volume. Rat studies suggest that this proess is omplete in 48 hours (and hene the working definition of aute versus hroni hyponatraemia). The ion hannels involved in the eletrolyte shifts in the first phase of volume hange are an area of ative researh. 7 Those involved in steady state volume regulation the pump-leak balane mehanism are different from those involved in regulatory volume derease in response to hypotoni hallenge as well as from J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

4 NEUROLOGY IN PRACTICE Definitions Hyponatraemia: Na +, 136 mmol/l Severe hyponatraemia: Na +, 120 mmol/l Aute hyponatraemia: hyponatraemia known to be of less than 48 hours duration or developing at a rate of. 0.5 mmol/hour Chroni hyponatraemia: hyponatraemia known to be of more than 48 hours duration or developing at a rate of, 0.5 mmol/hour Toniity (synonym: effetive osmolality): that portion of total osmolality that has the potential to indue transmembrane water movement the regulatory volume inrease involved in hypertoni hallenge. The relative proportions of the ontribution of organi and inorgani osmolytes involved in regulatory volume derease in mie has been alulated. The most signifiant is potassium (29%), followed by hloride (19%); the amino aids (of whih taurine, glutamine, glutamate, aspartate, and glyine are partiularly signifiant) ontribute 15%. Sodium is only the fourth most signifiant (13%). Other organi osmolytes ontribute the rest. Corretion of hyponatraemia The reaumulation of eletrolytes lost in response to a hypertoni environment is not the same proess in reverse as their loss in adaptation to hroni hyponatraemia. One inorgani ion shifts have been exhausted, if the rate of rise of toniity is faster than the rate at whih organi osmoles an be synthesised and/or transported into the ell, the ell will shrink. It appears that oligodendroytes are espeially vulnerable to death, presumably from volume loss. It is perhaps here that the nutritional status of the patient plays its part, impairing the ability to regenerate organi osmoles. At present we annot assess this ability, and so it is not really possible to determine a threshold rate of hange that an be guaranteed to be universally safe. Reommendations for safe rates of Na + rise are based on animal models and published series of CPM. It is with a sense of inevitability that one reads of a role for apoptosis being suggested in any disease. It is well established, however, that the persistent physial shrinkage of ells indued by hypertoni stress leads to ell death in a variety of ell types. Oligodendroytes are partiularly vulnerable to apoptosis in a number of disease states a partiularly striking example is hypoxi brain damage in infants. There is indeed some evidene for apoptosis in CPM. In a neropsy study of the ratio of pro- to anti-apoptoti markers, there appeared to have been a shift in favour of apoptosis in oligodendroytes (the apoptoti related death markers death reeptor 3, Bax, and Bak all showed modest inreases). 8 It is intriguing to note that apoptosis reruits a partiular potassium hannel (the two pore domain potassium hannel) that is used for homeostati volume regulation. Is it possible that osmoti stress via ativation of these ion hannels leads to inadvertent triggering of the apoptoti asade? Management of hyponatraemia Damned if we do, damned if we don t was one author s view in an exellent review artile on the management of hyponatraemia, referring to the dilemma of rapid versus slow orretion. 5 Others have disussed the management of hyponatraemia in a ritial review. 9 They make the point that one annot resolve this management dilemma by balaning the inidene of CPM in those treated rapidly with the mortality of hyponatraemi brain oedema treated too slowly, as one does not know that those patients in this latter group would have survived with rapid treatment; they may in fat have been beyond resue. Only two out of 200 ases reviewed in the literature of CPM ourred as a onsequene of rapid orretion of aute hyponatraemia developing after admission to hospital, both in post-prostatetomy patients who had had bladder infusion of glyine and both hyperammonaemi. It is a ommon experiene of general physiians that the rapidity of rise in the onentration of Na + within the first day of treatment, even when avoiding hypertoni saline, and with every intention of supervising a gradual inrease in Na +, may be surprisingly great: the Na + onentration seems to run away. This happens in animal models as well. Mortality of severe hyponatraemia In most series the mortality from severe hyponatraemia is between 40 50%. A few series, partiularly in seleted subgroups, suh as those in the intensive therapy unit (ITU), have a lower but still signifiant mortality of about 10 20%. This high mortality rate has led some authors to argue that the mortality is inreased by slow orretion and that the issue is one of balaning this mortality against the risk of induing CPM/EPM. Their onlusions have met, however, with onsiderable ontroversy The logi of this argument has been hallenged as one annot assume that rapid orretion of severe symptomati hyponatraemia in a patient will result in reovery many of these patients are already brain dead from erebral oedema at presentation, and beyond resue however they are managed. Evaluation of the ause of hyponatraemia It is not unommon for the ause of the hyponatraemia to remain somewhat louded at the point when a neurologial onsultation is sought. Pseudohyponatraemia Pseudohyponatraemia is a problem that has not quite disappeared in the UK. If a signifiant non-aqueous phase is inluded in the volume of serum sampled the Na + result will be diluted aordingly. It is worth disussing this with your MLSO; in our hospital the blood gas analyser has a diret measuring Na + eletrode, whih an irumvent the problem. It is lassially desribed in hyperlipidaemi states, hypertriglyeridaemia being the important fator, and in multiple myeloma (administration of intravenous immunoglobulin has the potential to mimi this) Syndrome of inappropriate ADH (SIADH) This may be over-diagnosed. In a retrospetive series of patients admitted with severe hyponatraemia rarely had urine osmolality or urinary sodium heked, and it is diffiult to see how the ause of hyponatraemia ould be learly established. Essential for diagnosis is euvolaemia, normal renal funtion, and absene of hypothyroidism or Addison s hypoadrenalism. iii25 J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

5 iii26 Cerebral salt wasting This ours most harateristially with subarahnoid haemorrhage. Its existene has always been somewhat ontroversial Treatment of aute hyponatraemia The benign onsequene of rapid orretion of aute hyponatraemia is illustrated by a retrospetive report of the lak of any sequelae of rapid orretion of severe symptomati aute hyponatraemia in 27 episodes among 13 patients with psyhogeni polydipsia. 10 Despite rapid and large rises in serum sodium, none of the patients had neurologial sequelae. The diffiulty in linial pratie is that it is extremely diffiult to assess the hroniity of hyponatraemia in the patient admitted with severe hyponatraemia, so that if there is any doubt one should assume the hyponatraemia is hroni rather than aute. Treatment of hroni hyponatraemia Most authors seem to agree that the orretion of aute hyponatraemia an be rapid; for hroni hyponatraemia the reommendations have shown an obvious trend (tables 3 and 4, fig 4). Disussion with olleagues suggests that the figure of not more than 10 mmol/l/day is the onsensus figure most neurologists arry around in their head. The most reent reommendation is not in exess of 8 mmol/l/day. Some suggest stabilising the patient in a mild hyponatraemi state after the initial orretion. Laureno and Karp suggest that it may be impossible to define a level of orretion that is always ompletely free of risk. This problem is ompounded as the treating physiian has only indiret ontrol over the rate of Na + rise whih may orret faster despite their best intentions. There is no better example of the axiom that disorders of a metaboli nature should be treated at a rate ommensurate with the rate at whih they have developed. One should probably inlude any potassium (K + ) orretion in the total daily orretion. Corretion into hypernatraemi onentrations should definitely be avoided: why add insult to injury? Other metaboli aetiologies Hypernatraemia had already been reported in assoiation with CPM before a landmark study of burns patients with CPM that firmly established hypernatraemia as an assoiation. Table 3 Published reommendations Too rapid is.20 mmol/l over 3 days (Norenberg) If Na +,105 mmol/l orret at 2 mmol/l/hour for first 20 mmol/l, then allow to drift to normal. If Na + >105 mmol/l orret at 2 mmol/l/hour to mmol/l (Ayus 1985) Not.12 mmol/l/day for first day, and subsequent days slower (Sterns ) 2.5 mmol/l/hour and no more than 20 mmol/day (Berl 1990) Not.8 mmol/l/day (Oh 1995) 15 mmol/l in 24 hours (Kumar and Berl 1998),10 mmol/l/day (Laureno and Karp 1997),,10 mmol/l/day in first 24 hours and less on subsequent days (Karp and Laureno 2000) Should not exeed 1 2 mmol/l/hour and never more than 8 mmol/l/ day (Brown 2000) Should not exeed 8 mmol/l on any day of orretion (Adrogue, 2000) Although reommendations for slow orretion have been standard for years, what is regarded as slow has hanged. Table 4 Pratial management strategy What sodium shifts have ourred? Confirm that the ause of hyponatraemia has been reliably established Is there the opportunity to reindue hyponatraemia? Has imaging been done? In a ventilated patient CT is aeptable; MRI desirable; repeat imaging neessary if negative Is the patient loked-in? Do nursing and medial staff appreiate this? Do relatives understand? Are relatives in the piture re prognosis? If EPM present is dopaminergi treatment an option? CT, omputed tomography; EPM, extra-pontine myelinolysis; MRI, magneti resonane imaging. Hypokalaemia has been reported as a possible trigger. However as a priori, even the lowest serum K + ompatible with life annot produe a very signifiant shift in effetive osmolality, it has not reeived the attention it might deserve. A review of published ases in 1994, in whih the values of both Na + and K + were given, found that 66 of the 74 ases reported were hypokalaemi. 11 The signifiane of other eletrolytes is less ertain: assoiations with hypophosphataemia, magnesium, and lithium therapy have all been proposed, but in all ases either hyponatraemia was present or the Na + was not measured at the beginning of the illness. INVESTIGATIONS: EVOKED POTENTIALS AND IMAGING Before omputed tomography (CT) brainstem auditory evoked potentials were used, but modern imaging has superseded its use. CPM an be seen on CT, but magneti resonane imaging (MRI) is frequently striking (fig 5) and is the imaging tehnique of hoie, having a greater sensitivity for CPM than CT and superior apaity for the demonstration of the lesions of EPM. Hyperintense lesions are seen on T2, and hypointense lesions on T1 weighted images. The lesions are nonontrast enhaning. The timing of the appearane of lesions on MRI may be signifiantly delayed, and if the diagnosis remains likely a repeat imaging study at days may reveal lesions not apparent on early sans. The reverse situation has been reported in whih the MRI hanges harateristi of CPM were seen without any pathologial hanges on postmortem examination one month after imaging (a 64 year old man with a heart transplant, Na mmol/l to 134 mmol/l in 24 hours). The authors argued that what had been seen on MRI was reversible oedema. mmol/l/day Figure 4 NEUROLOGY IN PRACTICE Year of publiation Maximum suggested orretion of sodium in 24 hours. J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

6 NEUROLOGY IN PRACTICE A reent series of ases found an absene of prognosti information from MRI, with neither the duration nor extent of abnormalities orrelating with outome. 12 Diffusion weighted imaging (DWI) findings have been reported. DWI might have the apability of deteting lesions undetetable on T2. A single ase report has just been published showing altered DWI in a patient within 24 hours of tetraplegia at a time when onventional MRI findings were inonspiuous. Few of the ases urrently being reported in the literature are supported by pathologial evidene. The MRI appearane of CPM is so harateristi that one feels justified in making the diagnosis on MRI harateristis alone. This has the potential for misdiagnosis and may aount for ases without harateristi shifts in Na +. It has been argued that large asymptomati pontine lesions are unlikely to be CPM lesions. TREATMENT OF CPM/EPM AND POTENTIAL FUTURE THERAPIES There have been no trials. Case reports or very small series have tended to reinfore the pereption that this ondition has an exessively high mortality. At present supportive treatment is all that an be reommended with ertainty. Reports on small ase series or single ase reports of treatments inluding steroids, intravenous immunoglobulin, and thyrotrophin releasing hormone, have all shown good outomes but are diffiult to interpret for the above reason. Intriguing is the possible benefit of reinduing hyponatraemia, as has been reported in animal studies and two human ases. 13 Animal work on the administration of organi osmolytes during the orretion phase shows this to be a potential treatment. PROGNOSIS The prognosis of the osmoti demyelination syndrome has long been regarded as bleak, primarily beause before CT/ MRI this was a postmortem diagnosis: it was not until 10 years after its first desription that the diagnosis was made in life, and that patient subsequently died of their disease. The introdution of CT and subsequently MRI allowed for onfident diagnosis in life and inevitably survival and asymptomati ases started to be reported. The most reent Figure 5 (A) Magneti resonane image (MRI) of a 57 year old woman admitted with hepati enephalopathy. History of alohol onsumption of half to a whole bottle of whisky a day. Admission Na mmol/l, K mmol/l, GT 1067 mmol/l, bilirubin 106 mmol/l, alanine transaminase 133 mmol/l. Treated with intravenous normal saline; Na mmol/l at 36 hours and 128 mmol/l after a further 24 hours. Initial improvement, deterioration on 11th hospital day with pseudobulbar palsy and flaid quadriparesis. (B) MRI of a 61 year old man with symmetrial lesions of EPM involving basal ganglia and thalami; lesion of CPM was also present (MRIs ourtesy of Dr Garrett MGann.) Osmoti demyelination syndromes: key points Consider in a patient who has failed to reover as expeted after a severe illness requiring intravenous fluids Consider in a patient manifesting psyhiatri symptoms after suh an illness, even if imaging is negative Na + rise need not be in exess of 10 mmol/l/day for ondition to develop. There may be no safe limit for the rate of Na + rise; readers would be prudent to review reommended limits of aeptable Na + rise at regular intervals as the reommended limit has steadily fallen Prognosis is not uniformly bad MRI hanges may be delayed MRI severity is not prognosti Extra-pontine myelinolysis may manifest in a number of different ways, the linial piture an evolve over days, and some of the manifestations may be symptomatially treatable The opportunity to present suh ases at medial grand rounds should be onsidered in order to foster interspeiality disussion of hyponatraemi management large series of 34 ases showed that only two died, 10 survived but were left dependent, 11 had some defiits but were independent, and 11 reovered ompletely. 12 An individual prognosis is diffiult. Neither linial features nor extent of radiologial hange are preditive. In summary, the outome may be death, disability, or reovery to a virtually normal level of funtion. One major pratial problem is that from the relatives point of view there has been a deterioration in the patient s ondition sine admission whih has usually followed a period of initially gratifying improvement. This situation would be easier for everyone to deal with if the possibility of late deterioration is disussed as soon as severe hyponatraemia is deteted and orretion is begun. It is important to larify with all medial staff that good reovery is possible so as not to misinform resusitation deisions. CONCLUSION The osmoti demyelination syndrome is a ompliation of treatment of patients with profound, life threatening iii27 J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.

7 iii28 hyponatraemia. It ours as a onsequene of a rapid rise in serum toniity in individuals with hroni severe hyponatraemia who have made intraellular adaptations to the prevailing hypotoniity. Elevation in serum sodium is the overwhelming ontributor to the rise in toniity, but potassium elevation may ontribute. Malnutrition and aloholism seem to predispose. Evidene for other eletrolyte shifts (with the exeption of prolonged hypernatraemia) as ausative is flimsy. ACKNOWLEDGEMENTS I d like to express my thanks to Dr Garrett MGann of Cheltenham General Hospital for MRI sans and to Dr Tim Moss of Frenhay Hospital for pathologial illustrations of CPM. REFERENCES 1 Adams RA, Vitor M, Manall EL. Central pontine myelinolysis: a hitherto undesribed disease ourring in aloholis and malnourished patients. Arh Neurol Psyhiatry 1959;81: The original report, well worth reading 2 Wright DG, Laureno R, Vitor M. Pontine and extrapontine myelinolysis. Brain 1979;102: Goht A, Colmant HJ. Central pontine and extrapontine myelinolysis: a report of 58 ases. Clin Neuropath 1987;6: NEUROLOGY IN PRACTICE 4 Karp BI, Laureno R. Central pontine and extrapontine myelinolysis after orretion of hyponatraemia. The Neurologist 2000;6: Co-authored by the author of the dog model of CPM, a strikingly lear aount with a useful historial perspetive. 5 Berl T. Treating hyponatremia: damned if we do and damned if we don t. Kidney Int 1990;37: Sterns RH. The management of symptomati hyponatraemia. Semin Nephrol 1990;10: Two useful reviews by nephrologists. 7 Okada Y, Maeno E, Shimizu T, et al. Reeptor-mediated ontrol of regulatory volume derease (RVD) and apoptoti volume derease (AVD). J Physiol 2001;532:3 16. An interesting review of the state of understanding of the ion hannels involved. 8 DeLua GC, Nagy Zs, Esiri MM, et al. Evidene for a role for apoptosis in entral pontine myelinolysis. Ata Neuropathol 2002;103: Oh MS, Kim H-J, Carroll HJ. Reommendations for treatment of symptomati hyponatremia. Nephron 1995;70: Cheng JC, Zikos D, Skopiki HA, et al. Long-term neurologi outome in psyhogeni water drinkers with severe symptomati hyponatremia: the effet of rapid orretion. Am J Med 1990;88: Lohr JW. Osmoti demyelination syndrome following orretion of hyponatremia: assoiation with hypokalemia. Am J Med 1994;96: Menger H, Jorg J. Outome of entral pontine and extrapontine myelinolysis. J Neurol 1999;246: Prognosis better than hitherto thought, no useful prognosis from MRI. 13 Oya S, Tsutsumi K, Ueki K, et al. Reindution of hyponatraemia to treat entral pontine myelinolysis. Neurology 2001;57: J Neurol Neurosurg Psyhiatry: first published as /jnnp on 16 August Downloaded from on 14 August 2018 by guest. Proteted by opyright.