OBJECTIVES: Three symptoms — impaired gait, cognition, and incontinence — define idiopathic normal pressure hydrocephalus (iNPH). To predict whether iNPH patients will benefit from shunt surgery, the tap test (TT) or continuous lumbar drainage (CLD) may be employed. This study's goal is to evaluate the cost-effectiveness of TT and CLD in comparison to the standard of care, in which all patients with suspected iNPH underwent shunt surgery, from the perspective of the Brazilian Public Health System.

METHODS: It was developed a decision tree model. The analysis considered the expenditures associated with TT, CLD, clinical consultations, and shunt surgery, as well as the accuracy of the tests and the likelihood that the procedure would be successful and any risks, such as stroke, significant bleeding, and meningitis. Utilities were based on a study that assessed the profitability of shunt surgery for iNPH patients.

RESULTS: Based on slight QALYs losses (0.02 and 0.01) and cost increases (U$ 88.90 and U$ 176.47) for TT and CLD, respectively, usual care dominated both strategies. While skipping shunt surgery in 13.4% and 6.4% of patients who might benefit, TT and CLD lowered the number of needless procedures by 26.9% and 22.6%, respectively. The likelihood that an operation would be effective, its cost, and its utility had the biggest effects on ICER.

CONCLUSIONS: Disregarding the modest magnitude of losses in QALYs and the small rise in expenses, there is still a trade-off in using TT and CLD to indicate shunt surgery for patients with suspected iNPH. While these strategies can help patients by preventing unnecessary shunt surgeries, some of those who would benefit would be mistakenly thought to be avoiding shunt surgery.