Serum osmolarity and blood viscosity as a potential explanation for the pathophysiology of neuroleptic malignant syndrome.

Neuroleptic malignant syndrome (NMS) is a rare but life-threatening side effect. NMS patients usually develop dehydration and fluid-electrolyte imbalance. In this study, we aimed to investigate serum osmolarity and blood viscosity in patients with NMS. This was a retrospective case-control study including 32 admissions of 27 patients with the diagnosis of NMS. As a control group, 31 non-NMS episodes of hospitalizations of the same patients were included. Serum osmolarity of NMS group was 301.83 ± 20.27 mOsm/L and control group was 294.20 ± 5.92 mOsm/L. Serum osmolarity of NMS group was statistically significantly higher than the controls ( = .018). Whole blood viscosity (WBV) at high shear rate (HSR) value of NMS group was 16.17 ± 1.48 and control group was 16.50 ± 1.38 ( = .331). Regarding WBV at low shear rate (LSR) values, also no statistically significant difference was observed between groups. LSR values of NMS and control group were 39.86 ± 30.11 and 47.41 ± 28.43, respectively ( = .387). Our findings indicate that serum osmolarity of NMS group was statistically significantly higher than the controls. In terms of blood viscosity, there was no statistically significant difference between groups. Higher serum osmolarity in NMS patients than controls may be a reflection of a relative hemoconcentration in NMS.KEY POINTSNMS is usually associated with dehydration resulting in fluid-electrolyte imbalance.We compared the NMS episodes with non-NMS hospitalizations (as control group) of the same patients.Serum osmolarity was statistically significantly higher in NMS group than the controls.There was no statistically significant difference between groups in terms of blood viscosity.