The predictive value of the tap-test in normal pressure hydrocephalus

Abstract

Normal pressure hydrocephalus (NPH) represents 1 to 12% of dementias. It is characterized by gait disturbance, progressive mental deterioration and urinary incontinence, associated with enlargement of the ventricular system and normal cerebrospinal fluid (CSF) pressure. In typical cases, gait disturbance is the first and most salient sign, followed by forgetfulness or mild dementia, psychomotor retardation, apathy and, later on, urinary urgency or incontinence. These cases present minor diagnostic difficulties and they are the most likely to improve after shunting. Differential diagnostic problems may, however, arise in some patients with atypical or incomplete clinical manifestations, as well as in patients with "subcortical" dementia such as Parkinson's disease, progressive supranuclear palsy and Binswanger's disease, which is the most common cause of the syndrome. In these cases, the results of computerized tomography (CT), magnetic resonance imaging (MRI) or radionuclide cisternography (RC) can be inconclusive or insufficient to establish a correct diagnosis and particularly to predict which patients will improve after shunting, hence the need to develop better methods for selecting patients to surgery. Therefore, we introduced into our Department of Neurology (UNICAMP's Medical School) the CSF tap-test (TT), which consists of measurements of gait pattern and psychometric functions before and after the removal of 50 to 100 mL CSF by lumbar puncture (LP).

Normal pressure hydrocephalus: Diagnostic and predictive evaluation

“…To this end, the best clinical predictors of good surgical outcome are short disease duration, high cognitive scores (mild or no dementia), gait disturbance preceding mental deterioration, dilation of temporal horns, and small sulci. 12 , 13 , 25 , 51 , 57 Nevertheless, the positive predictive value of the clinical-tomographic data alone is no greater than 65%, 25 and therefore must be improved upon by using complementary prognostic tests. As regards radionuclide cisternography, ICP monitoring and lumbar infusion tests, we agree with other authors 3 , 56 that none of these tests can confirm whether the patient will benefit from surgery, although they are able to show malfunctioning of CSF dynamics.…”

“…At the UNICAMP hospital, in Campinas, Brazil, we have attempted to improve the predictive value of the one tap version of CSF-TT since 1988 by increasing the amount of CSF removed and the drainage duration. 19 , 30 , 57 , 58 The selection of subtests takes into account that they should (1) be sensitive to NPH motor manifestations and measure cognitive functions that usually improve after LP and shunting; (2) be suited even for illiterate subjects, on account of the high illiteracy rate of our population of patients (about 15%); and (3) be low cost and easy and rapid to administer by neurologists in ambulatory outpatients. In order to rule out other diseases, we carried out a comprehensive investigation including CT or MRI, radionuclide cisternography, CSF analysis, laboratory tests, the Mini-Mental State Examination, 59 , 60 CAMDEX, 61 and use of Hachinski Ischemic Scores for vascular dementia, 62 ICD-10 63 and NINCDS-ADRDA criteria for Alzheimer’s disease, 64 besides gait and memory tests.…”

Neuroimaging in normal pressure hydrocephalus

“…Radionuclide cisternography (RC), intracranial pressure monitoring (ICP) and lumbar infusion tests can show CSF dynamics malfunction, but none are able to confirm whether the patient will benefit from surgery. 6 , 7 A 'positive' RC (with ventricular reflux and convexity block) can be seen in other dementia disorders and even in healthy subjects, thus having questionable predictive value. Most clinicians suggest it should no longer be performed, 8 and the International INPH Guidelines 9 have not included it as an option, since it does not improve the diagnostic accuracy of identifying shunt-responsive cases.…”