Serious adverse events following Normal Pressure Hydrocephalus surgery
Introduction
Normal Pressure Hydrocephalus (NPH) is a neurological condition characterized by cerebral ventriculomegaly and clinical features of cognitive, gait, and urinary dysfunction. Our current understanding about the epidemiology, pathophysiology, and treatment of NPH is limited. Prevalence estimates vary substantially from 27 cases/100,000 inhabitants in door-to-door community-based studies of older adults to as much as 1300 cases/100,000 in prospective studies with random population sampling [1]. Clinically, the proper selection of patients for surgical intervention typically involves a clinical evaluation, neuroimaging, and a diagnostic trial of cerebrospinal fluid (CSF) removal, none of which are supported by high levels of evidence [2].
Given the widely existing uncertainty about patient selection, the 2015 American Academy of Neurology (AAN) practice guidelines explored the published literature on NPH aiming to provide clinicians with a clear set of parameters to weigh when considering NPH surgery [2]. Three prospective level III studies in those guidelines estimated a pooled serious adverse event rate of 11% following NPH surgery. Subsequently, a level B recommendation was issued, stating “because of significant adverse event (AE) risk, risks and benefits should be carefully weighed.” This recommendation highlights the uncertainty, for both patients and providers, surrounding how best to balance the estimated benefits vs. risks of elective neurosurgery in older adults weighing NPH intervention.
Common adverse events following NPH surgery include subdural hematomas (SDHs) as a result of iatrogenic pressure changes induced by ventricular drainage and central nervous system (CNS) infections which may relate to the presence of indwelling hardware in the form of a ventricular shunt catheter that crosses the blood-brain barrier. These CNS specific adverse events (AEs) are not well estimated by conventional pre-operative risk stratification models. Moreover, AEs typically occur many months after initial surgery, suggesting that the small number of prospective studies that have published on risks of surgery to date may be under-estimating the risks of NPH surgery by tracking AEs over only a relatively short post-operative time period [3].
We conducted a retrospective review of all patients at the University of Michigan (UM) seen in our multidisciplinary NPH clinic over a 4-year period who have undergone an initial surgery for treatment of NPH. We hypothesized the rate of serious adverse events (SAEs) would be greater than the 11% rate reported in the practice parameter guidelines.
Section snippets
Materials and methods
A multidisciplinary Neurology-Neurosurgery NPH clinical throughput has been in place at the UM since February of 2014. All referred patients are initially seen by a Neurologist (V.K) to evaluate for non-NPH causes of neurological disability. Following this evaluation, patients whose clinical features are suggestive of NPH and who are interested in further NPH work-up are seen in a separate appointment by our Neurosurgical Team (J.H, E.W.), who typically conduct a diagnostic CSF drainage
Results
Over a 4-year period between 2/2014 and 12/2017, 162 new patients were evaluated in Neurology NPH clinic for consideration of NPH. 22 of these patients ultimately underwent neurosurgical intervention with placement of a ventricular shunt. Mean follow-up duration from the time of surgery to the last Neurosurgery/Neurology note was 12.7 months (SD: 8.6) with a range of 1–31 months. Eleven SAEs were observed in 10 patients out of the 22 total (Table 1).
Eight SAEs were coded as probably/definitely
Discussion
In our single center cohort, surgical intervention for NPH carries significant risk for serious adverse events related to surgery at a rate that is higher than estimates previously reported. Many SAEs occurred more than 3 months after the time of surgery suggesting that prospective studies monitoring post-op AEs for shorter durations of time may underestimate the risk of NPH interventions. These findings raise questions about the long-term safety of NPH shunt surgery but should be interpreted
Acknowledgements
We wish to thank all of the patients in this study
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