gms | German Medical Science

Objective: We compared the results of computerized overnight monitoring (ONM) of intracranial pressure (ICP) and the results of computerized lumbar infusion studies (LIS) with regard to their predictive power concerning shunt responsiveness in patients with suspected normal pressure hydrocephalus (NPH). The study aimed to find parameters replacing the need for a 3-day lumbar drainage in selecting patients with a high likelihood of positive shunt response.

Methods: 20 patients with probably or possible NPH according to the recently published iNPH guidelines underwent ONM using ICP+ Software (Cambridge University) after implantation of a pressure transducer (Codmann ICP Express). After 1-2 nights of monitoring the LIS with constant rate infusion (1,5 ml/min) was performed. From ONM the following parameters were derived: median, minimal and maximal ICP, power of slow wave activity (SLOW), ICP pulse wave amplitude (frequency domain, AMP) und RAP coefficient, which describes the cerebral reserve capacity. From LIS were calculated: CSF outflow resistance (R_out), pressure volume index (PVI), and elastance (E). All patients received a 3-day lumbar drainage trial and the clinical effect was assessed. Only patients experiencing objective benefit were shunted.

Results: 15 patients responded positively to lumbar drainage and received a shunt (NPH+). The others were considered as not having NPH (NPH-). Only RAP index and PVI/E were significantly different between groups (p<0.03), both indicating a lower compliance and more severe compromise of cerebral reserve capacity, despite normal ICP, in NPH+ patients. R_out, however was not significantly different between groups. The best predictive power for positive drainage response yielded the combination of RAP>0.6 and E<0.1, with a sensitivity of 0.77, a specificity of 0.8, and a positive predictive value of 0.91.

Conclusions: The most significant parameters in respect to ONM were the RAP index for describing cerebral reserve capacity and LIS, elastance and PVI for describing compliance,. New theories looking at the underlying aetiology of so-called communicating hydrocephalus, favour a primary loss of intracranial compliance resulting in ventriculomegaly and symptoms of NPH. Our results seem to support the importance of compliance for NPH patients. The limited number of patients prevents definite conclusions, however, a possible way to avoid a 3-day lumbar drainage trial seems to be the combination of ONM and LIS.