Idiopathic normal pressure hydrocephalus (iNPH) is a clinical condition characterized by symptoms of gait disturbance, cognitive dysfunction, and urinary disturbance. In contrast, progressive supranuclear palsy (PSP) is a progressive neurodegenerative disease characterized by supranuclear gaze palsy, akinetic rigidity, gait disturbance, and dementia. PSP manifests various clinical phenotypes that mimic other diseases and occasionally present iNPH-like presentations. Our previous publication showed that PSP develops iNPH-like magnetic resonance imaging (MRI) features more frequently than other neurodegenerative diseases. It is thus sometimes challenging to distinguish iNPH from PSP. Recently, we showed that patients with PSP, particularly those with iNPH-like MRI findings, often demonstrate amelioration of their gait disturbance following a spinal tap or shunt operation. Moreover, our study revealed that both patients with iNPH and PSP often manifest a placebo effect that can be evaluated by implementing a sham spinal tap. Therefore, although a positive response to a spinal tap has been thought of as a distinct feature of iNPH, it may not be useful in differentiating iNPH and PSP. However, in clinical practice, comparing the response to a spinal tap with that of a sham spinal tap may help accurately specify patients with iNPH or PSP who definitively respond to the shunt operation.