Specific patterns of cognitive impairment in patients with idiopathic normal pressure hydrocephalus and Alzheimer's disease: a pilot study

Objectives-Eleven patients with idiopathic normal pressure hydrocephalus (N PH) were selected from an initial cohort of 43 patients. The patients with NPH fell into two distinctive subgroups: preshunt, group 1 (n=5) scored les s than 24 on the mini mental state examination (MMSE) and were classified a s demented and group 2 (n=6) scored 24 or above on the MMSE and were classi fied as nondemented. Methods-All patients were neuropsychologically assessed on two occasions: p reshunt and then again 6 months postshunt. Group 1 completed the mini menta l state examination ((MMSE) and the Kendrick object learning test (KOLT). I n addition to the MMSE and KOLT, group 2 completed further tasks including verbal fluency and memory and attentional tasks from the CANTAB battery. Ni ne of the 11 patients also underwent postshunt MRI. Results-Group 1, who, preshunt, performed in the dementing range on both th e MMSE and KOLT, showed a significant postoperative recovery, with all pati ents now scoring within the normal nondemented range. Group 2, although sho wing no signs of dementia according to the MMSE and KOLT either preshunt or postshunt, did show a specific pattern of impairment on tests sensitive to fronto-striatal dysfunction compared with healthy volunteers, and this pat tern remained postoperatively. Importantly, this pattern is distinct from t hat exhibited by patients with mild Alzheimer's disease. Eight of the nine patterns of structural damage corresponded well to cognitive performance. Conclusions-These findings are useful for three main reasons: (1) they deta il the structural and functional profile of impairment seen in NPH, (2) the y demonstrate the heterogeneity found in this population and show how sever ity of initial cognitive impairment can affect outcome postshunt, and (3) t hey may inform and provide a means of monitoring the cognitive outcome of n ew procedures in shunt surgery.