osmotic demyelination syndrome ( ods ) , which is also known as central pontine myelinolysis ( cpm ) , has been found to occur after the rapid correction of severe hyponatremia ( 1 ) . the clinical manifestations of ods are known to develop for 2 - 6 days after a rapid elevation of the serum sodium level . the symptoms are often irreversible or only partially reversible , and they include dysarthria , dysphagia , tetraparesis , behavioral disturbances , lethargy , confusion , disorientation , and coma ( 2 ) . when cpm develops after the rapid correction of hyponatremia , plasma exchange ( pe ) may be a beneficial therapy . bibl et al . successfully treated three young female patients by intensive plasmapheresis soon after confirming a diagnosis of cpm ( 3 ) . all three patients had undergone the correction of severe hyponatremia at 3 - 5 days before the onset of the neurological symptoms . a 71-year - old japanese woman with hypertension and dyslipidemia was admitted for progressive dysarthria and gait disorder . she had been taking nifedipine cr ( 40 mg / day ) , imidapril ( 10 mg / day ) , valsartan ( 80 mg / day ) , rosuvastatin ( 2.5 mg / day ) , trichlormethiazide ( 4 mg / day ) , zolpidem ( 10 mg / day ) , teprenone ( 1.5 g / day ) , magnesium oxide ( 990 mg / day ) , torimebuchiren ( 300 mg / day ) , for a few years . she looked confused but was aware of her name , and the place and time . the laboratory data on admission is shown in the table ; briefly , hyponatremia ( na 101 meq / l ) , hypochloremia ( cl 68 meq / l ) , and slight hypokalemia ( k 3.5 meq / l ) . head computed tomography ( ct ) and brain magnetic resonance imaging ( mri ) revealed no abnormalities , and electrocardiography ( ecg ) showed no evidence of arrhythmia . we suspected that her consciousness disorder was due to severe hyponatremia . since her serum sodium level had fallen from 135 meq / l a few days before admission to our hospital , we concluded that her hyponatremia had chronically progressed . we started correcting her serum sodium level with an intravenous infusion of normal saline by calculating the sodium dosage and infusion speed . on the second hospital day she became alert and we allowed her to ingest meals that contained about 10 g of nacl . on the third hospital day , her serum sodium level had risen to 120 meq / l . because we thought the correction was too rapid her serum sodium level was still 120 meq / l and her serum phosphate level was 1.0 mg / dl . her serum phosphate level was 2.5 mg / dl on the second day of hospitalization and decreased to 1.9 mg / dl on the morning of the third day . we prescribed sodium phosphate and water - soluble vitamins with saline or half saline to treat the deficiency while supplying few calories . at first after her consciousness deteriorated the following day , we performed head ct and brain mri . we also consulted neurologists , who ruled out ods based on the diagnostic imaging and physical findings . a few hours later , we found her snoring , and gradually her oxygen saturation level started to fall . electroencephalography ( eeg ) and lumbar puncture did not help in making a diagnosis . within 2 days spastic tetraparesis and deep tendon hyperreflexia were noted , and the babinski reflex was observed . her tetraparesis worsened day by day and it soon became difficult for her to stand , move her face , or swallow . the transient consciousness and respiratory disorder might have been due to refeeding syndrome or wernicke encephalopathy . but we could hardly explain the progressive tetraparesis and recurrent nerve palsy after she became alert . on the 26th day of hospitalization , brain mri revealed a fresh high signal region in the pons and the bilateral basal ganglia , which led us to make a diagnosis of ods ( fig . 1 ) . on the 39th day of hospitalization , we started consecutive pe , at a rate of 2 - 3 sessions per week for total of 6 sessions ( fig . since her body weight was 55 kg and her hct value was 33% , her estimated plasma volume was 550.065(1 - 0.33)=2.4 l. we exchanged a total volume of 3,840 ml of fresh frozen plasma ( ffp ) ( approximately one and a half times the volume of her plasma ; 2.41.5=3.6 l ) . her spastic tetraparesis showed significant improvement after the start of pe therapy , and she was able to stand by herself and walk after the second session of pe . the high signals in the pons and bilateral basal ganglia were reduced in size but remained after the completion of pe therapy ( fig . she was able to eat and drink without aspirating , and walked on foot unassisted on the 111th day of hospitalization . rbc : red blood cell , u- : urinary , osm : osmolality , un : urea nitrogen , na : sodium , k : potassium , cl : chrolide , cr : creatinine , wbc : white blood cell , tp : total protein , ast : aspartate aminotransferase , alt : alanine aminotransferase , ldh : lactate dehydrogenase , ck : creatine kinase , bun : blood urea nitrogen , tg : tryglyceride , ldl : low density lipoprotein , crp : c - reactive protein , egfr : estimated glomerular filtration rate , posm : plasma osmolality , b.e . bass excess , igg / a / m : immunogloblin g / a / m ,   ch50 : complement hemolytic activity , c3/c4 : complement , ana : anti - nuclear antibody , tsh : thyroid stimulating hormone ,   hanp : human atrial natriuretic peptide , pra : plasma renin activity , acth : adrenocorticotrophic hormone , avp : arginine vasopressin ,   pt ( inr ) : thrombin time ( international normalized ratio ) , aptt : activated partial thromboplastin time ,   fdp : fibrin and fibrinogen degradation products , hbs : hepatitis b surface , hcv . : anti - hepatitis c , sts : serological test for syphilis a fluid attenuated inversion recovery ( flair ) sequence of brain mri . the laboratory findings on admission , including a serum osmolality of 215 mosm and a serum sodium level of 108 meq / l , showed hypoosmotic hyponatremia . the patient 's lower limbs were slightly edematous on admission to the emergency department , but her chest x - ray showed a normal cardiac silhouette and no evidence of pleural fluid . a loss of appetite for a few days resulted in a fractional excretion of sodium value of 0.47% and a fractional excretion of urea nitrogen value of 33.9% , which indicated mild hypovolemia . both the urinalysis findings and her serum human atrial natriuretic peptide level ( 32.7 pg / ml ) ruled out severe hypovolemia . a rapid acth test showed no evidence of adrenocortical insufficiency , and a crh / trh / gnrh / ghrh tolerance test ruled out hypopituitarism . the serum avp level of 2.6 pg / ml was high for an osmolality of 215 mosm , and we suspected syndrome of inappropriate secretion of antidiuretic hormone ( siadh ) . no obvious cause of siadh , such as malignancy , inflammatory disease , or central nervous system disorder was detected other than the physical stress caused by admission , and mental stress prior to admission . an examination to investigate sodium and other electrolyte disorders , led to a diagnosis of hyponatremia due to thiazide diuretics . it is well - known that thiazide diuretics sometimes cause hyponatremia , and that it can happen after taking diuretics for a few years . some drugs induce hyponatremia when taken with thiazide diuretics ( 4,5 ) . the etiology of ods is not clear , but it is considered to be an iatrogenic disease that is caused by a rapid rise in the serum level of sodium ( 1 ) . the damage to the blood - brain barrier by osmotic change is thought to result from the exposure of the brain to myelinotoxic substances ( 6,7 ) . the speed at which the serum sodium level is corrected should be decided carefully when treating chronic hyponatremia ; however , it is not unusual for the serum sodium level to differ from the expected values ( 2 ) . the re - induction of hyponatremia is reported to be beneficial for preventing ods due to a rapid correction of hyponatremia ( 8,9 ) . other treatments , such as the administration of trh , corticosteroids ( 6,10 ) , immunoglobulins ( 11 ) , and pe ( 3 ) were suggested by case reports . minocycline is said to be effective in preventing ods in the rat models ( 12 ) . however , there are no proven , effective treatments for ods . in the present case , it took more than one month to diagnose ods . in the chronic phase of ods , we could not expect the same effect of a re - lowering serum sodium level . since plasma apheresis is known to be effective in treating demyelinating neuropathy ( 13 ) , we decided to treat our patient using pe . the direct effects of pe on the blood - brain barrier have not been proven ; however , her symptoms improved dramatically , immediately after the initiation of pe . the improvement of the nerve cells or neuron system is unlikely to occur with a single pe session . the previous case reports in which pe was shown to be beneficial in the treatment of acute - phase ods indicate that the improvement of ods - associated symptoms following pe could be explained by the removal of myelinotoxic substances , which are involved in the pathogenesis of ods . on the other hand , in the present case , the introduction of pe in the chronic phase improved her neurological symptoms , suggesting that myelinotoxic substances work not only as an exacerbating factor but also as a suppressor of neural activity . it has been reported that 31% of ods patients died and that 31% required life - supporting therapy after one year of follow - up ( 14 ) . there are likely to be cases that are thought to be uncurable in which physicians give up treatment after diagnosing ods . not all the cases require plasma exchange ; however , it could be an effective treatment for chronic ods .
a 71-year - old japanese woman presented with progressive fatigue , lethargy , dysarthria and a gait disorder . 
 her laboratory data revealed hyponatremia ( na 101 meq / l ) , and we started correcting her serum sodium level . within a few days , she became comatose , bedridden , and was intubated . 
 we diagnosed osmotic demyelination syndrome ( ods ) and started performing plasma exchange ( pe ) on the 39th day of hospitalization . 
 she fully recovered after starting pe , and was discharged on foot unassisted . 
 pe can be a beneficial treatment in patients with chronic ods .