Assessment of patients affected by INPH after external lumbar drainage: what is the better timing?

Background: Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible neurological condition characterized by cerebrospinal fluid (CSF) accumulation contributing to clinical symptoms. Removal of excess CSF can lead to improvement, and among the available approaches, external lumbar drainage (ELD) offers superior diagnostic accuracy. However, the optimal timing for patient evaluation following ELD remains unclear. Methods: We recruited 54 adult iNPH patients, assessed at baseline (T0), 48 hours (T1), and 10 days (T2) after ELD. Balance performance was measured using clinical scales for both static and dynamic balance, while gait parameters were instrumentally assessed at patient usual pace, both without and with concurrent cognitive dual task. Results: Clinical scales showed no significant change at T1, while a statistically significant improvement emerged at T2. Instrumental gait analysis revealed more robust changes at T2, involving a greater number of parameters and reaching stronger significance levels. Regarding potential ELD responders, more patients exceeded the Minimal Detectable Change thresholds for both clinical and instrumental measures at T2. Conclusions: Although current literature lacks clear guidance on timing, our findings suggest that extending follow-up to 10 days provides a more comprehensive and reliable assessment of potential improvements. These results should be validated in larger studies with additional follow-up to confirm the long-term predictive value of ELD for shunt surgery.