Cognitive impairment in patients with idiopathic normal pressure hydrocephalus
Ogino A, Kazui H, Miyoshi N, Hashimoto M, Ohkawa S, et al.;
Commented by , 20 Feb 2006
Aim of the study
To compare the neuropsychological profile of mild cases of idiopathic Normal Pressure Hydrocephalus (iNPH) and probable Alzheimer’s disease (AD), which may facilitate the diagnosis of iNPI.
Method
21 patients with iNPH and 42 patients with AD were matched 2:1 by age, gender, Mini Mental State Examination (MMSE) scores, after a careful clinical work-up. The neuropsychological tests used for comparison included the Alzheimer’s Disease Assessment Scale-cognitive part (ADAS-cog), the Wechsler Memory Scale-Revised (WMS-R), and the Wechsler Adult Intelligence Scale-Revised (WAIS-R).
Subjects were allowed to complete subtests with a time limit but the extra time was noted as "achievement scores". The cognitive function of all iNPH patients was assessed before spinal taps and shunt surgery. Group differences were quantified with the two-tailed Student’s t test.
A step-wise discriminant function analysis was used to identify the neuropsychological tests that best distinguish iNPH from AD.
Results
The mean MMSE score of the iNPH group was 21.6, and that of the AD group 21.7. The iNPH group did significantly better than the AD group in the ADAS-cog orientation test and the WMS-R general memory and delayed recall subtests, but worse in the WMS-R attention/concentration subtest, the WAIS-R digit span, arithmetic, block design, and digit symbol substitution subtests, the performance IQ.
The achievement score of the arithmetic subtest of the WAIS-R was significantly worse in the iNPH group. The best discriminant factors were the WMS-R general memory, the WAIS-R digit span, the WAIS-R digit symbol substitution, and the WAIS-R similarities scores, with a prediction of 85.7% of iNPH patients and 85.7% of AD subjects.
Professor Gauthier's comments
These data indicate that iNPH patients had more severe impairment of attention, psychomotor speed, and calculation relative to AD patients, but better on general memory, delayed recall and orientation.
The authors explain these differences by a more severe frontal lobe involvement in iNPH relative to AD, at least in the early stages, most likely related to disturbances in the subcortical area connecting to the frontal cortex, whereas the relative sparing of the memory and orientation suggest preservation of the medial temporal lobe structure (visible on MRI) and function.
It would be useful if the authors of this excellent study could report on the neuropsychological tests after shunting their iNPH patients, since the classic clinical wisdom is that there is little improvement to be expected after this procedure.
This publication highlights the importance of neuropsychological tests as a component of the clinical and radiologic assessment of subjects in early stages of dementia who present with atypical features of AD, e.g. early gait impairment and urine incontinence.
Although iNPH is very rare compared to AD, arrest or slowing down of progression may be possible using shunting.