Outcome of Shunting for Idiopathic 'Normal Pressure Hydrocephalus'

Abstract & Commentary

By John J. Caronna, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Caronna reports no financial relationships relevant to this field of study.

Synopsis: Normal pressure hydrocephalus remains a clinical diagnosis and standardized clinical assessments predict a positive response to shunting in most patients.

Sources: Klinge P, et al. One-year outcome in the European multicentre study on iNPH. Acta Neurol Scand 2012; DOI:10.1111/j.1600-0404.2012.01676X. Hellstrom P, et al. A new scale for assessment of severity and outcome in iNPH. Acta Neurol Scand 2012; DOI:10.1111/j.1600-0404.2012.01677X.

The authors assessed the 1-year outcome after shunt surgery in patients with idiopathic normal pressure hydrocephalus (iNPH), that is, NPH of unknown cause. Patients (n = 142) were prospectively included in the European Multicenter Study of iNPH that evaluated the predictive value of the CSF tap test (TT) and resistance to CSF outflow studies (to be reported in a separate article). The present study reports outcome in patients in whom the diagnosis of iNPH was based solely on the clinical and radiological findings without regard to the results of CSF TT and CSF outflow studies.

Based on clinical and radiologic criteria, patients were classified as "typical" (iNPHt) in 61% or "questionable" (iNPHQ) in 39%. A diagnosis of iNPHt by clinical criteria required a gait disturbance affecting tandem walking, turning, stride length, and base. Patients diagnosed as iNPHQ had less typical gait disturbances. Patients with iNPHt had mild-to-moderate cognitive impairment (MMSE Score > 21); those with more severe cognitive deficits were classified as iNPHQ. The presence of incontinence was not used for classification.

The MRI criteria for iNPHt and iNPHQ were an Evans index > 0.30 and evidence of communicating hydrocephalus. Patients with iNPHQ also had moderate cortical atrophy and moderate-to-severe leukoaraiosis.

At 12 months after shunt surgery, outcome was assessed in 115 patients by the modified Rankin Scale (mRS) and the iNPH grading scale of four domains: gait, neuropsychology, balance, and continence. Sixty-nine percent of patients had improved according to the mRS by one step or more, and 84% according to the iNPH scale. The improvement by domains was gait 77%, neuropsychology 63%, balance 56%, and incontinence 66%. There were no differences in comorbidities or signs and symptoms between responders and non-responders to surgery. Classification of iNPH as "typical" or "questionable" did not affect level of improvement.

Twenty-eight percent of patients experienced complications of surgery that were either conservatively (13%) or surgically (15%) treated. Only one patient had a hematoma that required evacuation. These results strongly support shunt surgery for patients with clinical and MRI features suggestive of iNPH.

Commentary

This study provides evidence that long-term improvement can be sustained in patients after shunt surgery. In the past, it was common for patients who initially did well after shunting to deteriorate over months as the mechanical characteristics of their CSF dynamics changed over time. The present durability of good results is probably, in part, the result of the use of programmable ventriculoperitoneal shunts. In the present series, shunt adjustments were made 76 times in 36 patients (31%).

The remarkable improvement rate in this series was substantially higher than the 50% reported in a review of studies not using any supplementary tests for the selection of patients for surgery.1 One reason for the high rate of successful shunting may be the early and accurate recognition of the typical clinical and radiological phenotype of iNPH in these patients. Another reason is probably the use of a new, more sensitive iNPH scale to measure outcome. Motor improvement in 69% of patients also was measured by the modified Rankin Scale (MRS).

NPH remains fundamentally a clinical diagnosis. Nevertheless, clinical features alone cannot distinguish between responders and non-responders to shunt surgery. The evaluation of patients with a suspected diagnosis of NPH has been more hindered than helped by attempts to develop confirmatory tests and procedures to predict the response to shunt surgery. At present, most clinical tests such as CSF drainage have a high positive-predictive value but a poor negative-predictive value. More than half of suspected NPH patients with a negative CSF TT can be expected to respond to shunt surgery.

The decision to refer a patient for shunt surgery remains based on a detailed history and neurological examination, together with an MRI of the brain and a lumbar puncture for CSF examination and pressure measurement. Therefore, we await, with interest, the final results of the European iNPH study that combines clinical and radiologic evaluations with CSF TT and CSF outflow resistance studies and correlates them with outcome after shunt surgery.

Reference

1. Marmarou A, et al. Guidelines for management of idiopathic normal pressure hydrocephalus: Progress to date. Acta Neurochir Suppl 2005;95:237-240.