Annals of Neurosciences, Vol 13, No 2 (2006)
Annals of Neurosciences, Volume 13, Issue 2 (April), 2006
NORMAL PRESSURE HYDROCEPHALUS: A CASE REPORT
Corresponding author
Dr. Rakesh Shukla
Professor of Neurology, Department of Neurology,
King George's Medical University, Lucknow-226003
Ph No. 0522–2257090, Fax No. 0522–2257090
Abstract
Normal pressure hydrocephalus is an entity characterized by triad of gait disturbance, cognitive impairment and urinary incontinence. It is a communicating hydrocephalus that despite normal opening pressure at lumbar puncture is reversible in significant proportion of patients by cerebrospinal fluid (CSF) diversion. Since the time this entity has been described, efforts are going on by researchers to diagnose this entity at the earliest so that it can be intervened before irreversible stage develops. Here we are reporting a case of Normal Pressure Hydrocephalus who presented with gait abnormality and mental slowness and was benefited with timely intervention of hydrocephalus with shunt surgery.
Key Words: NPH, Shunt Surgery
Introduction
Hakim and Adams described normal pressure hydrocephalus in 1965 (1). This apparently paradoxical condition has prompted to a considerable number of studies aimed at explaining the pathophysiology of the disease and identifying the best candidates for CSF shunt surgery (2). It has also been called as “chronic hydrocephalus”. Reversible dementias account for 20% of all dementias and NPH is responsible for 0.4% of treatable dementias. Various diagnostic tests have been proposed to diagnose this clinical syndrome as early as possible so that it can be intervened at the earliest so as to halt the process. We are reporting one such case of Normal Pressure Hydrocephalus who responded dramatically with lumboperitoneal shunt.
Case
An sixty five year old non diabetic, hypertensive, retired professor gentleman was admitted in neurology ward with complaints of difficulty in walking for 1 year, forgetfulness of 6 months duration and urinary urgency of 5 months duration. Difficulty in walking was in the form of hesitation in initiating steps, slowness in gait and difficulty in turning around the corners of the path when asked to do so immediately. This problem progressed slowly and he started taking support of one stick and use to avoid going long distances and walked more cautiously. He use to freeze at times while walking. After few months, he developed difficulty in executing daily routine activities, took longer time in doing daily activities and required some assistance He also had difficulty in word finding and money handling, started forgetting recent events, names of distant relatives but would remember if given some hint. He lost the promptness in handling daily activities, which he had before. There was no history of visuospatial disorientation, apraxias or agnosias. He also complained of urinary urgency which was more in the night time and hesitancy and occasional incontinence. There was no history of stroke in the past. Personal and family history was not significant. General physical examination revealed pulse rate of 84/minute, blood pressure 140/90 (on antihypertensive drug). Neurological assessment revealed Mini Mental State Examination (MMSE) score 24/30, recall and calculation was impaired, also reaction time was longer. His frontal lobe tests were normal. Motor system examination showed normal tone and power in all four limbs, deep tendon jerks were normal and both planters were flexer. Gait assessment revealed wide based stance, steps were slow, short, and shuffling and feet did not rise much above the ground as if they were glued. There was hesitation at the start of steps and at times he could not continue walking as if freezed and then required cues to take further steps. With this background patient was investigated on lines of cognitive impairment with gait difficulty from the onset. Hematological and biochemical parameters were normal. He was subjected to neuro-imaging of brain in form of Magnetic Resonance Imaging (MRI) which showed symmetric dilatation of all the ventricles. The sulci were preserved and perihippocampal fissures were normal excluding the possibility of ex vacuo dilatation. There were no significant white matter abnormalities. These findings were seen on T1, T2 weighted and T2 Flair images (Figure 1&2). A diagnosis of Normal Pressure Hydrocephalus(NPH) was made and a CSF Tap Test was done; 50 ml of CSF was drained. The opening pressure was 190 cm of water and cyto-biochemical examination of CSF showed proteins -29 mg%, sugar – 45 mg%( corresponding blood sugar 100mg%), Cells <5,all lymphocytes. Hematological and biochemical parameters were normal. Pre and post test assessment of gait and cognitive functions was done after first hour and was repeated three hourly till twelve hours, which revealed marked improvement in gait. The stride length increased and number of steps to walk a fixed distance also decreased. There was no hesitation at initiation of steps and less difficulty in taking turns. Subsequently over next few weeks, his executive functions in performing day to day activities also improved. He took lesser time in carrying out daily activities and acts were more fluid. Repeat MMSE showed upgrading of initial score, both recall and calculation improved, reaction time decreased .In face of such marked improvement with CSF tap test, patient underwent lumboperitoneal shunt surgery following which there was near complete recovery of both cognitive and gait disturbance. Patient was examined four months after shunt surgery, the shunt is functioning well and he is maintaining the improved cognitive and gait status. Patient is still under follow up to look for shunt functions and its related complications.
Discussion
NPH consists of constellation of gait disturbance, urinary disturbance and memory impairment. Gait disturbance is first to appear and is the most common symptom. In NPH there is disproportionate dilatation of cerebral ventricles, which may be caused by CSF absorption defect, and raised CSF outflow resistance which explains some of the aspects of pathophysiology (3). Dilated ventricles causes reduction of blood flow as a result of stretching of anterior cerebral arteries over corpus callosum which decreases the metabolism in areas supplied by these arteries, stretching of periventricular white matter disturbing fibers for gait and urinary continence and stretching of cholinergic fibers involved in memory. There is increase in transmantle pressure also (4). Idiopathic NPH is the most common variety in which no inciting event has been identified but NPH can develop secondary to traumatic subarachnoid hemorrhage, meningitis, cerebral infarction, Pagets disease of cranium, mucopolysaccharidosis and achondroplasia. These probably interfere with CSF absorption at the arachnoid granulations. Idiopathic hydrocephalus presents in 6–7 decade where as secondary NPH may be present at any age. The classic triad of NPH yields a 65% positive predictive value and 82% negative predictive value in a series of idiopathic NPH patients and diagnostic tests should be evaluated for predictive values above these levels (5). Various diagnostic tools have been laid to diagnose this condition and to assess the various prognostic factors related. These are categorized into CSF hydrodynamics study and neuro-imaging techniques. CSF hydrodynamics study include CSF tap test in which 30–50 ml of CSF is removed by lumbar puncture and observation for clinical improvement is done. Cognitive functions are assessed by MMSE and by various psychometric tests like identical form tests, reaction time test and gait by time taken to walk a fixed distance and velocity of gait along with Romberg's test are assessed pre and post tap. We performed this test in our patient and clinical improvement was recorded following which patient was subjected to shunt surgery. The CSF tap test could not predict post shunt improvement in gait, variables in activities of daily living or neuropsychological variables, even though certain patients experienced an acute improvement of gait with CSF drainage. It has been proposed that gait testing is the best predictor of shunt outcome, but this has been criticized because of high false negative rate which is approximately 50% (6). If clinical suspicion is high and patient dose not improve with single tap test, repeated lumbar punctures are indicated for next 1–2 days .Clinical reassessment is done 3 hours after the tap and improvement may be delayed by 1–2 days after large volume tapping. Patient who does not improve with CSF tap test may be subjected to extended drainage for 5 days during which external lumbar drainage is done. Studies have shown the sensitivity and specificity of this drainage technique up to 100%. Various methods have recently been described which can predict the post shunt improvement. These are presence of episodic A or B waves on intracranial pressure (ICP) monitoring indicating the preserved compensatory mechanisms of brain against episodic rise in CSF pressure. CSF pressures in NPH remain high normal (150–180mmHg). A single, limited in time CSF pressure measurement by lumbar puncture yields a poor estimation of the real ICP profile in NPH patients (2). In one study, simultaneous blood flow velocity of cerebral vessels by transcranial Doppler study and ICP recording correlated closely with each other. Continuous lumbar drainage has shown to predict outcome, but the risk of meningitis and radiculitis needs to be considered. A comparison of CLD over 3 days with ICP monitoring produced favorable predictive results for CLD with sensitivity of 97%, specificity of 60 %, positive predictive value of 84 % and negative predictive value of 90 % (7).
Fig. 1: T2flair image of the patient
Fig. 2: T2 image of the patient
Neuro-imaging tools which guide us in diagnosing NPH are computed axial tomography (CT) Scan and MRI of brain. Early CT features of NPH are dilatation and rounding of temporal horns with preserved perihippocampal fissure, ballooning of frontal horns, septal angle becoming acute. Later, third ventricle also balloons and their wall lies parallel. The Evan index (ratio of maximum width of frontal horns to the maximum width of inner table of the cranium) increases and can easily be followed in serial CT scans. Higher Evan ratio ( > .40) is not correlated with clinical improvement (8). Good results after shunting can also be obtained in patients showing a frontal horn ratio > .50 on CT studies.
MRI is superior to CT scan as it is able to image in sagittal and coronal planes and has greater sensitivity for alternative diagnosis such as multi-infarct dementia and it is also able to identify CSF flow effects .On MRI, the hydrocephalic ventriculomegaly can be assessed by measurements of ventricular diameters. Periventricular/subcortical hyper intensities are common in NPH patients. Tedeschi et al found that 8 of 11 patients of NPH had hyper intensities and 57% of these patients had good clinical outcome from shunting (9). Krauss et al found a significant negative correlation between the presence of white matter lesions and clinical outcome, but it was impossible to predict the outcome in individual patient since these lesions preclude satisfactory outcome (10). In our patient there were no significant white matter abnormalities that could be correlated with his good outcome following shunt surgery. CSF flow voids at the region of aqueduct gives a distinct “Jet sign” created as result of decreased CSF absorption which allow larger volume of CSF to move through the aqueduct. CSF flow voids do not predict the post shunt outcome or its failure. Radionucleoid cisternography may diagnose communicating hydrocephalus but fails to predict shunt outcome (11). Various diagnostic modalities have upsurged in the recent past to diagnose NPH at an early stage and to predict the outcome of shunt surgery. CSF tap test is a simple, easy to perform test that has a relatively fair power of prognosticating the outcome of shunt surgery.
References
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