Incidence of Idiopathic Normal-Pressure Hydrocephalus in Northern Spain.

BACKGROUND: Although the incidence of idiopathic normal-pressure hydrocephalus (iNPH) can be 1.20 cases/1000 inhabitants/year in individuals ≥ 70 years old, in most series, the incidence of shunt-responsive iNPH appears to be <1/100,000 inhabitants/year. We report the results of a prospective 10-year longitudinal study of the incidence of iNPH in a northern Spanish population. METHODS: In a stable population of 590,000 inhabitants served by a single neurosurgical department, we periodically asked all primary care practitioners, neurologists, and geriatricians to refer for iNPH screening any patient with ventricular dilation who was complaining of motor disturbances, cognitive impairment, or sphincter dysfunction. RESULTS: From January 2003 to December 2012, 293 patients were referred with suspected normal-pressure hydrocephalus. In 187 patients, iNPH was diagnosed; 89 of these patients were classified as probable iNPH, and 98 were classified as possible iNPH. Cerebrospinal fluid diversion was performed in 152 patients, and 119 showed a good outcome. The incidence of iNPH was significantly greater in male patients and patients >60 years old and increased exponentially with age. After age 60, the standardized age- and sex-adjusted incidence rates for iNPH, shunt surgery for iNPH, and shunt-responsive iNPH were 13.36 cases/100,000 inhabitants/year, 10.85 cases/100,000 inhabitants/year, and 8.55 cases/100,000 inhabitants/year. No differences were detected in the response rate between probable and possible iNPH (80.52% vs. 76.00%; P = 0.497). CONCLUSIONS: Even with a protocol for patient referral in place, reported iNPH incidence was lower than predicted, reflecting a persistent problem of underdiagnosis in our population.

Epidemiology of Idiopathic Normal Pressure Hydrocephalus: A Systematic Review of the Literature.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is an important cause of gait disturbance and cognitive impairment in elderly adults. However, the epidemiology of iNPH is relatively unknown, largely as a result of the paucity of specifically designed population studies. This systematic review aims to assess the prevalence and incidence of iNPH. METHODS: A systematic literature review on the epidemiology of iNPH was conducted using MEDLINE/PubMed searching for articles published up to June 2014. RESULTS: The inclusion criteria were met by 21 studies. Of the studies, 12 were specifically designed for detecting cases of iNPH; however, only 4 were prospective. In people >65 years old, pooled prevalence obtained from specific population studies was 1.3%, which was almost 50-fold higher than that inferred from door-to-door surveys of dementia or parkinsonism. Prevalence may be higher in assisted-living and extended-care residents, with 11.6% of patients fulfilling the criteria for suspected iNPH and 2.0% of patients showing permanent improvement after cerebrospinal fluid diversion. The only prospective population-based survey that reported iNPH incidence estimated 1.20 cases/1000 inhabitants/year, 15-fold higher than estimates obtained from studies based on hospital catchment areas. The incidence of shunt surgery for iNPH and shunt-responsive iNPH obtained from incident cases of hospital catchment areas appears to be <2 cases/100,000 inhabitants/year and 1 case/100,000 inhabitants/year, respectively. No population-based study reporting the real values for these 2 parameters could be found. CONCLUSIONS: iNPH appears to be extremely underdiagnosed. Properly designed and adequately powered population-based studies are required to characterize the epidemiology of this disease accurately.