 One of the major issues is whether the false negative tests mostly occur in the same population. In these patients the INPH might be caused not so much by a CSF circulation disorder but by parenchymal disease. From our clinical experience we think that different patients have false negative tests, we frequently encounter cases with a positive tap test and a negative infusion test or the reverse. This is also shown in a study by Kahlon et al. who performed an infusion test and a tap test in 68 patients suspected of NPH. Both tests agreed in only 45 and they were both negative in 31 of patients 7. 