====== Slope until reaching the plateau ======

[[Idiopathic normal pressure hydrocephalus diagnosis]] is based on clinical, radiological, and hydrodynamic data of [[cerebrospinal fluid]] (CSF) obtained by invasive methods such as [[lumbar infusion test]], which is used to determine the resistance to CSF outflow ([[Rout]]). However, Rout has limitations, and its value as a predictor of valve response is questioned. Other variables can be obtained by the lumbar infusion test, such as the time to reach the [[plateau]] (TRP) and the slope until reaching the plateau (SRP). The objectives were to determine if SRP could be a predictor of response to ventriculoperitoneal shunt (VPS) and what variable (Rout versus SRP) would have a greater predictive value.

Patients with [[probable idiopathic normal pressure hydrocephalus]] who underwent a lumbar infusion test and were indicated for a VPS were retrospectively studied. Two groups were established, responders and non-responders. Rout, TRP (period between the start of infusion until reaching the plateau measured in seconds) and SRP (plateau pressure-opening pressure)/TRP) were obtained. For Rout and SRP, the receiver operating curves (ROC) with its areas under the curve (AUC) were calculated.

One hundred ten patients were included, being 86 responders (78.20%). Shunt responders had a significantly greater Rout (17.02 (14.45-20.23) versus 13.34 (12.10-16.28) mmHg/ml/min, p = 0.002) and SRP (0.049 (0.043-0.054) versus 0.031 (0.026-0.036) mmHg/sec, p < 0.001) and smaller TRP (641.28 (584.83-697.73) versus 777.65 (654.03-901.27) sec, p = 0.028) than non-responders. The AUC for SRP was greater than the AUC for Rout (0.763 (95 % CI 0.655-0.871, p < 0.001) versus 0.673 (95 % CI 0.595-0.801, p = 0.008), respectively), but the differences were not significant (p = 0.180).

SRP could be considered a predictor of response to VPS, and its accuracy tends to be better than Rout. So, this variable may be a useful tool to select shunt candidates among patients with probable iNPH.
((Otero-Rodriguez A, Arandia-Guzman DA, Pascual-Argente D, Ruiz-Martin L, de Oca JR, Garcia-Martin A, Torres-Carretero L, Uriel-Lavin R, Garrido-Ruiz PA, Rodriguez-Cedeño D, Cid-Mendes L. Slope until reaching the plateau: a new predictor of valve response obtained by lumbar infusion test for [[idiopathic normal pressure hydrocephalus]]. Acta Neurochir (Wien). 2023 Jun 22. doi: 10.1007/s00701-023-05670-y. Epub ahead of print. PMID: 37347295.)).