Predictors of shunt response in iNPH: differentiating responders, early and late non-responders, and the role of valve adjustments

Idiopathic normal pressure hydrocephalus (iNPH) is diagnosed based on a positive shunt response. However, up to 40% of patients who undergo ventriculoperitoneal (VP) shunting fail to exhibit sustained improvement. The management of iNPH remains challenging, particularly for non-responders who deteriorate despite surgery. We aimed to determine what features differentiate between long term versus short term responders and do valve adjustments affect their outcome? We included patients that underwent ventriculoperitoneal shunt surgery for iNPH between December 2006 and December 2016. Patients were stratified as early ( 6 months) non-responders, and responders. Descriptive statistics, time series plotting, chi-squared tests, and ANOVA analyses were used. Our cohort of 65 iNPH patients exhibited a mean follow-up of 3.75 years and consisted of 53.8% early non-responders, 15.4% late non-responders, and 30.8% responders. Comorbidities were distributed across all groups but did not significantly differentiate between response categories. A considerable subset experienced symptom deterioration after the six months mark. Shunt valve adjustments were more frequent in non-responders but did not prevent continued deterioration. In late non-responders, valve adjustments merely slowed symptom progression, without halting deterioration. Our study underscores that valve pressure adjustments in early non-responders, who likely never benefit from shunt surgery, are not effective, and highlights the emergence of a late non-responder phenotype, where symptom deterioration becomes evident 6 months post-shunting. Our findings outline the need to explore alternative treatment strategies for managing symptoms in iNPH non-responders, as well as prolonged follow-up regimens to monitor late non-responders.