Assessing Treatment Response in Idiopathic Normal Pressure Hydrocephalus: A Prospective Comparison of Outcome Measures

BACKGROUND AND OBJECTIVES: Assessment of treatment response in idiopathic normal pressure hydrocephalus (iNPH) lacks a universally accepted standardized outcome measure. Therefore, this study compared the disease-specific Gothenburg scale (GBS), the GBS without gait velocity, the modified Rankin Scale, the iNPH Grading Scale, and the 15-dimensonal health-related quality-of-life instrument against gait speed improvement to evaluate the responsiveness and discriminative ability of the GBS during a 12-month postshunting follow-up. METHODS: This was a prospective population-based cohort study in which patients undergoing shunt surgery were evaluated preoperatively and up to 36 months postoperatively. The primary analyses included the preoperative assessments and assessments at 3 and 12 months after shunt surgery. Responsiveness was measured using the standardized response mean (SRM), and the discriminative ability to detect gait speed improvement was analyzed using the area under the curve (AUC). RESULTS: The GBS was the most responsive and stable scale: SRM values 0.80 (95% CI, 0.67-0.93) at 3 months and 0.72 (95% CI, 0.57-0.87) at 12 months. Using the minimal clinically important difference (MCID) as the anchor, the corresponding AUCs were 0.85 (95% CI, 0.81-0.90) and 0.91 (95% CI, 0.86-0.95). The GBS without gait velocity showed similar performance with SRMs of 0.76 (95% CI, 0.63-0.88) and 0.68 (95% CI, 0.53-0.82) and AUCs of 0.82 (95% CI, 0.77-0.87) and 0.87 (95% CI, 0.82-0.93) at 3 and 12 months. The 15D showed the lowest responsiveness, failing to capture disease-specific changes. CONCLUSION: The GBS is a strong and highly sensitive scale for monitoring patients with iNPH. General and non-disease-specific outcome measures should only be used as complementary indicators accompanied by gait speed evaluations.