Normal pressure hydrocephalus.

Abstract

To the Editor: — A 79-year-old lady presented to the hospital following a fall. She had a 20-month history of increasing confusion. She lived alone in a ground floor flat but had become dependent on her daughter, requiring help with dressing, transferring and feeding. There were no abnormal neurological signs and she was able to walk a short distance with a Zimmer walking frame. For 10 months she was thought to have Alzheimer's disease. However, in view of the development of urinary incontinence and increasingly poor initiation of movement without paresis or Parkinsonism, normal pressure hydrocephalus was considered. The computed tomography (CT) scan showed gross dilatation of lateral ventricles and the third ventricle, and a shallow subarachnoid space. Overnight ventricular fluid pressure recordings, which we consider very important in this condition,1 showed a mean pressure of 20 mm Hg (normal, less than 10 mm Hg) and runs of B waves (Lundberg's spike-shaped waves as opposed to his plateau A waves, normally occurring once or twice per minute). A right ventriculoatrial shunt was implanted. She became mentally bright, continent and independent with a Zimmer walking frame within 5 days. By 12 days she was independent in self-care. She was discharged mobile with a stick to live in her own home independent of her daughter and remains very well 30 months later. This patient exemplifies three recurring problems. . Normal pressure hydrocephalus cannot be diagnosed by clinical features alone as the classical features, namely, dementia, incontinence and gait apraxia, may not all be present2, 3 and also occur in Alzheimer's disease. Although the patient eventually developed these features, her dementia had been present long before the others became apparent. . Although many feel that CT scanning is not indicated for patients with a long history of dementia,4, 5 this patient had a 21/2-year history of dementia but still improved with shunt surgery. In Petersen's survey, 17 out of 45 patients with normal pressure hydrocephalus (mean age 68 years) had histories of over 2 years, and half of these patients improved on shunting.3 . Although many feel that CT scanning is not indicated for patients with clinically severe Alzheimer's disease,6 this patient, had she been scanned initially, could have been treated 10 months earlier. Routine scanning in elderly patients with dementia is controversial with its low yield4 and, in view of the large numbers of patients involved, high cost. Moreover, when the diagnosis of normal pressure hydrocephalus is made, potential benefits of shunt surgery are reduced by surgical complications; these occurred in 31 % of Petersen's patients, although there were no deaths. Even so, the cost in both human and economic terms of missing this treatable diagnosis is profound. The continued massive expansion of the numbers of patients over 80 years of age with their 20% incidence of dementia, combined with the increasingly expensive costs of long-stay hospital accommodation, requires an increase in the numbers scanned to indentify patients with normal pressure hydrocephalus. Our criteria for the diagnosis of normal pressure hydrocephalus include dementia, ventricular dilatation on CT scanning thought to be due to hydrocephalus and by exclusion of other pathologies idiopathic, and typical overnight ventricular fluid pressure recordings. Clearly dementia due to other common treatable causes should be excluded first. We question whether the length or severity of the dementia or the presence of incontinence or gait ataxia should be part of the selection criteria for CT scanning. As ventricular fluid pressure recordings and insertion of a shunt are invasive procedures, they should not be contemplated if the patient is medically too frail; and informed consent from relatives is necessary.