Alzheimer's disease comorbidity in normal pressure hydrocephalus: prevalence and shunt response

The clinical impact of Alzheimer's disease pathology at biopsy was investig ated in 56 cognitively impaired patients undergoing shunt surgery for idiop athic normal pressure hydrocephalus (NPH). Cognition was measured by means of the global deterioration scale (GDS), the mini mental status examination (MMSE) and a battery of six psychometric tests. Gait was assessed using ob jective measurements of velocity and the ambulatory index (AI). The prevale nce of cases exhibiting neuritic plaques (positive biopsies) increased in p arallel with dementia severity from 18% for patients with GDS 3 to 75% for patients with GDS scores greater than or equal to 6. Patients with positive biopsies were more cognitively impaired (higher GDS and lower MMSE scores) as well as more gait impaired (higher ill scores and slower velocities) th an patients with negative biopsies. After surgery, gait velocity and AI sco res improved significantly and to a comparable degree for patients with and without positive biopsies. Similar proportions of positive and negative bi opsy patients also had improved gait as assessed by means of subjective vid eo tape comparisons. There were no significant differences between the biop sy groups in the magnitude of postoperative psychometric change or in the p roportion of cases exhibiting improved urinary control, Alzheimer's disease pathology is a common source of comorbidity in older patients with idiopat hic NPH where it contributes to the clinical impairment associated with thi s disorder. For patients accurately diagnosed with NPH, concomitant Alzheim er's disease pathology does not strongly influence the clinical response to shunt surgery.