Normal pressure hydrocephalus and the predictive value of presurgical tests

Abstract

ormal pressure hydrocephalus (NPH) is characterized by gait disturbance, progressive mental deterioration and urinary incontinence associated with enlargement of the ventricular system and normal cerebrospinal fluid (CSF) pressure, although episodes of increased CSF pressure do occur. In NPH, the excessive accumulation of CSF in the ventricular system is due to an impairment of CSF flow distally to the fourth ventricle ("communicating"). About 50% of NPH cases are "secondary" (due to meningitis, subarachnoid hemorrhage, trauma) while the other 50% are "idiopathic" (iNPH), usually occurring in the 7 th decade of life. Normal pressure hydrocephalus is a rare cause of dementia (less than 5% of all demented patients), with iNPH showing an annual incidence between 1.8/100,000 and 5.5/100,000 inhabitants, and prevalence ranging from 0.2% to 2.9% among individuals aged 65 years or older, based on surveys in northern Europe and Japan. Typical cases present with the triad of (1) gait disturbance as the first and most salient sign; followed by (2) an astheno-emotional syndrome characterized by difficulties in concentrating, increased irritability and fatigability, emotional instability, forgetfulness (more rarely, mild dementia), with psychomotor retardation, apathy, and sometimes a parkinsonian or depressive appearance; and, later on, (3) urinary urgency and/or incontinence. Gait disturbance is the cardinal sign in iNPH, typically a broad-based, short-step, slow magnetic gait with start hesitation and instability that is worst on turning, often with falls 1. It is not a genuine gait apraxia, since the patient can execute the walking movements without difficulty when lying down, despite freezing their gait when standing on their feet and trying to initiate walking 2. This gait impairment has been considered a gait ignition failure due to a frontal dysfunction or, more specifically, due to a frontal-basal ganglia disconnection, with uninhibited antigravity reflexes and co-contraction of agonists and antagonists during walking 3. Most of the iNPH syndrome is explained by a reduction of blood flow and metabolism in the frontal lobes, basal ganglia, medial thalamus, hippocampus, and anterior parts of periventricular white matter 4. In the typical patients, the diagnosis is almost straightforward and, after shunting, they are the most likely to improve, mainly in their gait disturbance. However, particularly in cases with atypical or incomplete clinical manifestations, there may be differential diagnostic difficulties, as the triad can be mimicked by other conditions such as Parkinson' s disease, progressive supranuclear palsy, and subcortical arteriosclerotic encephalopathy (Binswanger' s disease), which are much more common than NPH. In the elderly, other more common conditions may also explain the gait difficulties (arthrosis or arthritis, peripheral neuropathy, vestibular disease), urinary incontinence (prostate disease, chronic urinary tract infection), and mental deterioration (Alzheimer' s disease), particularly when the...

Normal-pressure hydrocephalus: A critical review

“…Souza et al’s study was critically reviewed by Damasceno 105 in an editorial, where the aforementioned result was found to be in accordance was the available literature. The need to determine whether other postural or gait parameters could better predict response to surgery was reinforced.…”

“…Additionally, Damasceno also supported repeated or continuous three-day external lumbar drainage (minimum of 150 ml CSF drained daily) as a way to enhance tap test sensitivity (50-100%) while maintaining a high positive predictive value (80-100%), compared to the one-tap CSF tap test with low sensitivity (26-61%). 15 , 105 …”