Prognosis
The diagnostic evaluation for surgical intervention is a central problem in the treatment of normal pressure hydrocephalus (NPH). In this context, the statement “Results are good if the indications are correct” still applies. There are quite substantial differences in reports of the results of treatments following shunt implantation. The reasons for this are the different views regarding the diagnostic evaluation for shunt implantation. Therefore, predictors must be found that have a high degree of predictive value in relation to the postoperative course.1
16.1 Predictors
Little or no expression of dementia or amnestic symptoms and the presence of iNPH symptoms for less than one year are positive predictors of the course of disease after shunt implantation. Patients with NPH in an early stage (with no atrophy of the brain) and a drainage resistance (Rout) of more than 15 Torr/mL/min, or patients with NPH in the late stage (with atrophy of the brain) and a drainage resistance (Rout) of more than 20 Torr/mL/min as a result of the intrathecal infusion test, have a positive prognosis. Because of better treatment results, the implantation of a hydrostatic valve is recommended in patients with NPH.2
Sorteberg et al3 showed that drainage resistance (Rout) using an intrathecal infusion test is a good predictor of the postoperative course following a shunt operation for idiopathic NPH (iNPH). In contrast, the authors described the intracranial pressure (ICP) measurement as having no predictive value. Poca et al4 came to the conclusion that, following a shunt operation in patients with NPH, a good improvement in ataxic gait and urinary incontinence can be achieved. In contrast, it is not possible to achieve a significant improvement in mental function with this surgical therapy. For this reason, those authors consider the presence of dementia to be a negative predictor. Murakami et al5 consider the measurement of regional cerebral blood flow using single-photon emission computed tomography diagnostics to have a positive predictive value in relation to the postoperative course of the illness. Gallia et al6 reported the cerebrospinal tap test, with an improvement in ataxic gait, to have a positive predictive value of 73% to 100%. However, there was a low sensitivity for this method of investigation, with a value of 26% to 61%, whereas a negative cerebrospinal tap test cannot exclude the presence of NPH. For this reason, the authors favor lumbar CSF drainage over a period of 48 hours with a positive predictive value of 80% to 100%. With this method of investigation, the authors quote a sensitivity of 50% to 100% and a specificity of 60% to 100%.
According to Chang et al,7 advanced age and male gender constitute negative predictors in relation to an improvement in cognitive function following a shunt operation in patients with NPH. Other authors8,9,10,11,12,13 have drawn attention to the importance of ataxic gait as the characteristic symptom of NPH and its improvement following a cerebrospinal tap test or lumbar cerebrospinal fluid drainage, as well as the symptom with the highest rate of improvement in the further course of the illness following shunt operation. In contrast to all of the previously mentioned authors, Delwel et al14 found no individual predictors with regard to the postoperative course following shunt operation. Also, parameters of the intrathecal infusion test, such as drainage resistance (Rout), were not helpful in relation to the results of the previously mentioned research groups with regard to prognostic evaluation. Other authors have described comorbidity (arterial hypertension, diabetes mellitus, peripheral and/or coronary large vessel diseases, cardiac diseases, cerebrovascular diseases, Parkinson disease) as a negative and statistically significant predictor of the quality of the clinical course of the disease in patients with iNPH following shunt therapy.10,15,16
16.2 Improvement of Prognosis
A meta-analysis within the scope of the guidelines for the management of iNPH of the Japanese Neurosurgeons Society reported improvement in 31% to 100% of the patients between 3 months to 2 years after shunt surgery. A longer follow-up period of 3 to 5 years produces an improvement rate of 61% to 91%.17 Depending on the individual symptoms, there is an improvement in disorders of gait in 58% to 90% and the amnestic symptoms or the symptoms of dementia in 29% to 80% of patients, and the symptom of urinary incontinence in 20% to 78% of patients.17 Patients with the classical Hakim triad show an improvement rate of 65% to 74%.17 In the guidelines of the U.S. iNPH Study Group,18 a rate of improvement of 72% to 80% in iNPH following a shunt operation has been reported. One year after surgical therapy, 30% to 95% of the patients continued to show improvement. The study reported an improvement rate of 78.9%, 2 to 3 years after the shunt operation, and a rate of 43%, 5 years after the shunt operation. In relation to the individual symptoms and a comparison of 5 years versus 1 year after the operation, it has been reported that the improvement in 76% of patients was reduced to 47% of patients and in those with urinary incontinence from 58% to 29%.18
▶ Table 16.1 summarizes the results of treatment according to the available literature. In this context, only those citations in the literature that have patient groups of more than 40 and whose periods of investigation were 6 months or more have been listed. In summary, it can be said that, in the case of patients with iNPH 1 year following the shunt operation, an improvement in the preoperative symptoms was seen in 59% to 91% of patients.14,19 The rate of improvement 2 to 3 years after the shunt operation was 61% to 85%.20 Our own research results, which included 5 years of follow-up after the shunt operation, produced an improvement rate of 60%.21
Authors, year | No. of patients with iNPH | Type of valve/valve pressure setting | Postinvestigation period (months)b | No. of patients showing improvement in clinical symptoms (%) |
Black 198022 | 62 | HAKIM medium pressure valve (DPV) | 36.5 | 61 |
Boon et al 200023 | 95 | HAKIM low and medium pressure valve (DPV) | 12 | 76 |
Delwel et al 200514 | 66 | Spitz–Holter medium pressure valve (DPV) | ≥12 | 59 |
