Osmotic demyelination syndrome in a patient of End-stage renal disease post-hemodialysis

Introduction

Osmotic demyelination syndrome (formerly called central pontine myelinolysis or CPM) is a well known clinco-pathologic entity characterized by edema and demyelination in the pons and extrapontine areas. It is classically related to an acute shift in serum osmolality, which is classically related to rapid correction of hyponatremia. Dysequilibrium syndrome is one of the metabolic complication of hemodialysis that may trigger osmotic demyelination syndrome.¹

Case Presentation

A 22 years old male with known case of chronic kidney disease (CKD) or end-stage renal disease (ESRD) on regular hemodialysis and resistant hypertension for which he was on treatment with four antihypertensive medications, presented with history of visual loss in the right eye 3 months ago which was sudden in onset. Initially there was blurring of vision of the right eye which had developed on following day of dialysis, which had progressed to total loss of vision , and there was only perception of light in the right eye.

The patient had noticed weakness of both lower limbs –post dialysis 2months ago. It had made a sudden onset and there was greater involvement of the right lower limb, and was associated with dragging sensation in lower limb with swaying towards right side and difficulty in gripping footwear, inability to climb stairs due to weakness.

He also complained of headache. No sensory symptoms had been observed with the weakness.

On examination, the patient showed non-pitting oedema of right lower limb with pulse of 92/ min, BP 170/100 mm Hg, higher mental function and speech were normal. Right eye showed only perception of light, and fundus revealed atropic retinal hole in superionasal and temporal quadrant with pale disc and sclerosed vessels. Left eye had good vision. Other cranial nerves were normal. There was hypertonia in all four limbs, and power in upper limbs were normal (5./5). Power in the lower limbs at hip 4/5, knee 4/5, ankle 4/5 with left foot drop with 0/5 power on dorsiflexion. Deep Reflexes were brisk and ankle jerk 4⁺ with clonus. Plantars were extensor bilaterally. Superficial reflexes corneal reflex , and abdominal reflex were normal. Sensations were normal.

Blood investigations showed Haemoglobin 11.1, total count 5900 cells / cmm, differential count – neutrophils 62%, lymphocytes 33%, eosinophils 3%, monocytes 2%, hematocrit 33.2%, MCV 84.9fl, MCH 28.9 pg , MCHC 33.4%, RBC 3.91 mill/cumm ,platelets 1.22lakhs/cmm, Urea 168, Creatinine 10.74 uric acid 6.39, serum sodium 135, serum potassium 6.8, serum chloride 103. Total Bilirubin 0.32, SGOT 24, SGPT 29, ALP 554, Total protein 7.25, Albumin 3.78, Globulin 3.50. CSF analysis was normal, Anti NMO antibodies negative. MRI imaging of the brain and spinal cord showed hyperintense areas in pons and cerebral peduncles, and D6 -D 8 spine regions (images 1- 3) suggestive of demyelination. The trend of serum sodium and urea levels before and after dialysis has been provided in the table 1.

Discussion

Adams et al first described central pontine myelinolysis in 1959.² The term “Osmotic Demyelination” became more popular when it was discoverd that extrapontine sites were also affected. Osmotic Demyelination Syndrome has been reported in normonatremic and hypernatremic patients as well as in conditions such as chronic alcoholism, liver transplantation, Diabetes mellitus, Hypokalemia, Pituitary surgery, and Chronic Renal Failure.³

Various mechanisms have been proposed for the devevlopment of Osmotic Demyelination syndrome. Primary pathophysiology is decreased capacity of the glial cells to large shifts of serum osmolartiy.⁴ Endo et al reported a 14% incidence of Osmotic Demyelination Syndrome in patients of ESRD on Hemodialysis.⁵ The proposed hypothesis for osmotic demyelination syndrome is osmotic injury to the endothelium from rapid changes in serum osmolality resulting in the release of myelinotoxic factors leading to the disruption of oligodendrocytes.⁶ The signs of CPM include dysarthria and dysphagia (secondary to corticobulbar fibre involvement), flaccid quadriparesis (from corticospinal tract involvement) which later becomes spastic, all from involvement of the basis pontis. if the lesion extends into the tegmentum of the pons and pupillary, oculomotor abnormalities may occur. There may be an apparent change in consciousness level reflecting the ‘‘locked-in syndrome’’ that a large lesion in this site is particularly liable to produce.⁷ Magnetic resonance imaging is the imaging of choice.

As serum sodium is the most important solute contributing to the serum osmolality and osmotic demyelination syndrome is classically related to the changes in serum sodium. There are few reports which have described osmotic demyelination syndrome in eunatremic patients as well which suggests that other solutes do play a role in the pathophysiology. Our case who is  a known case of ESRD on hemodialysis developed osmotic demyelination syndrome due to rapid changes in  the serum urea levels as his serum sodium had been stable throughout his admission in the hospital.

 Conclusion   

Our case highlights that osmotic demyelination syndrome is not related to hyponatremia. One must suspect osmotic demyelination syndrome in patient with eunatremia with chronic kidney disease on dialysis   as there are other electrolyes which can cause ODS, and in our case it was urea.