<qa>  What is the main issue with the false negative tests?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. 