Salt-free diet and pregnancy-related central pontine myelinolysis: “To diet or not?”

Abstract

Central pontine myelinolysis (CPM) is a rare medical condition that has primarily been associated with alcoholism, chronic malnutrition, certain surgical procedures, and serum sodium imbalances with rapid correction [1]. The condition has also been reported to be pregnancy-related, however complicated by hyperemesis gravidarum [2, 3], resulting in electrolyte disturbances, including hypokalemia [2] and possible hyponatremia [3]. Our present case further points out that CPM with minimal symptoms, could develop in normal pregnancy and could only be related to habitual salt-free diet. A previously healthy, normotensive, 38-year-old Greek female, gravida 1, 28 weeks pregnant, complained of right hemifacial paresthesias of increasing intensity over 10 days and was referred by her gynecologist for further evaluation. She had a 2-year history of salt-free diet, due to personal dietary habits, as well as no alcohol use. The neurological examination was normal, except for mild, right facial hypesthesia over the second trigeminal division. Extensive hematological and biochemical tests, including serum B12, folate, potassium, calcium, homocysteine, collagen, liver, kidney, venereal, viral, immunological disease, protein S and C, anticardiolipin antibodies, lupus anticoagulant and coagulation studies were either normal or unrevealing except for serum sodium level of 130 mmol/l (normal range 135–145 mmol/l). Brain MRI demonstrated a prominent hyperintensity in the central pons on T2 (Fig. 1a), FLAIR (Fig. 1b) and diffusion (Fig. 1c) weighted images (WI) and was compatible with CPM [1, 2]. The pontine lesion was not detected on T1WI and no contrast was given due to the pregnancy. Subsequently, CSF examination (cytochemistry, antibodies detection, electrophoresis) provided normal findings. She was only consulted to return to a ‘‘normal salt’’ diet and was discharged from the hospital. Two months later, after an uncomplicated delivery, the patient gave birth to a normal baby, the facial paresthesias had completely resolved, the serum sodium level was 142 mmol/l, nevertheless repeat MRI showed partial resolution of the central pontine hyperintensity on T2 (Fig. 2a), FLAIR (Fig. 2b) and diffusion WI (Fig. 2c). T1WI remained unrevealing, even after gadolinium infusion. Although there are mechanisms proposed for the pathogenesis of CPM [1], the exact pathophysiology remains unknown [1, 2]. In low serum sodium situations water flowing freely across cell membranes, causes vasogenic brain edema [1, 2] and indeed early pathological changes in CPM typically show microscopic intramyelinic edema and not demyelination [4]. In correcting the hyponatremia, if the rate of rise in tonicity is faster than the rate at which organic osmoles can be synthesized and/or transported into the cells, the cells will shrink and brain dehydration results in injury to oligodendrocytes [1, 2], with predilection of the lesion to the pons [1]. Nevertheless, there is still some controversy because CPM has been described in patients with normal serum sodium concentrations [3]. Additionally, patients with mild–chronic hyponatremia and slowly progressive replacement can also develop CPM, suggesting that some background predisposition is essential to the disease development [5]. The prognosis of CPM cases is highly variable, sometimes even fatal [1, 6] and other times P. Ioannidis (&) G. Balamoutsos D. Karacostas B’ Department of Neurology, AHEPA University Hospital, 54636 Thessaloniki, Greece e-mail: ioannidispanos@yahoo.gr