CSF tap test parameters and Short-Term outcomes in operated and non-operated patients with idiopathic normal pressure Hydrocephalus: A cohort study.

Background: Normal Pressure hydrocephalus (NPH) is treated by ventriculoperitoneal shunting. The cerebrospinal fluid tap test (CSF-TT) is widely used to identify candidates for shunt surgery in idiopathic NPH (iNPH). This study aimed to compare the CSF tap test responses and 24-week functional outcomes between patients with probable iNPH who underwent surgery and those who did not. Methods: This Ambispective cohort study included 40 patients with probable iNPH, as defined by the 2019 Japanese guidelines, from 2019 to 2024. All patients underwent a large-volume CSF-TT, and they were offered surgery based on the clinico-radiologic profile. Results: Twenty-four patients underwent ventriculoperitoneal shunt surgery, and 16 did not for various reasons. No significant differences were found in the baseline or 24-hour post-CSF tap test parameters between the groups. However, at 24 weeks, 62.5% of the operated patients showed at least a 1-point improvement in mRS. In contrast, only 14.3% in the non-operated group did, indicating the beneficial role of VP shunting in NPH. Those who were operated had a 10 times higher odds (95% CI 1.6-105) of achieving at least one point improvement in mRS at 24 weeks. Interestingly, 46.7% of patients whose mRS did not improve after CSF-TT but who underwent surgery still benefited from shunting. Conclusion: Shunt surgery leads to a favorable short-term functional outcome in patients with probable iNPH. However, the CSF-TT alone lacks sufficient discriminatory power to guide surgical decisions in a cohort of patients with clinico-radiological probable iNPH. A negative tap test should not preclude surgery in patients with supportive clinical and imaging features.