A case of idiopathic normal pressure hydrocephalus without enlarged ventricle and with negative tap test.

Background: Idiopathic normal pressure hydrocephalus (iNPH) is suspected by clinical symptoms and enlarged ventricles on imaging (Evans index [EI] >3.0). However, it remains unclear how to deal with patients who present with clinical symptoms but have no ventricular enlargement. Case Description: A 77-year-old man, whose symptoms were diagnosed as age-related (because of no ventriculomegaly and negative tap test) at a hospital visited 3 months prior, came to our clinic presenting with gait disturbance, cognitive decline, and urinary incontinence (iNPH triad). His responses to questions were very slow, and his Mini-Mental State Examination (MMSE) score was 11/30. The patient was unable to stand up from his wheelchair without assistance and had difficulty in taking the first step. On examination, his EI was 0.26 and tap test was negative. However, iNPH was strongly suspected because imaging showed unclear cerebral sulci at the parietal level, a narrow callosal angle, and a disproportionately enlarged subarachnoid space. Lumbar drainage was performed for 2 days, which improved his gait ability and increased his MMSE score to 17/30. We then performed shunt surgery. At 2 months after surgery, he was able to walk freely and independently around the hospital, his MMSE score improved to 25/30, and he was discharged home. Conclusion: Ventricle size is only an indicator for iNPH, and an EI cut-off of 0.3 is not an absolute indicator. Thus, even in the absence of ventricular enlargement, a thorough assessment is crucial in suspected iNPH cases.