CSF Tap Test Parameters and Short-Term Outcomes in operated and non-operated patients with idiopathic Normal Pressure Hydrocephalus: A Cohort Study
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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.
