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Normal Pressure Hydrocephalus 05 November 2004 Utility of Hakim’s triad 1.Gait difficulties most likely to improve after shunting magnetic phenomenon, postural instability, short stepped shuffling gait. Hyperreflexia. 2.Dementia less likely to respond to shunting subcortical / frontal impairment: trail making test 3.Urinary incontinence late sign urgency is common CT Ventricular enlargement out of proportion to cerebral atrophy, rounded frontal horns, enlarged temporal horns without hippocampal atrophy Miller Fisher tap test Easy, rapid, cheap High rate of false negative Pre & post LP - neuropsych for frontal lobe function - gait: ambulation velocity, up & go test, postural stability. For more information, see section on Miller Fisher Test.
MRI Flow void in aqueduct White matter hyperintensities Continuous Lumbar Drain 150-200 ml/d drainage for 3 days complications: radicular inflammation, meningitis sensitivity 97%, specificity 60% SPECT Cerebral blood flow No good correlate between changes in cerebral blood flow and outcome after shunting Even pre & post LP will not provide helpful pre-op prediction ICP monitoring A waves & excess B waves correlates well with good outcome post surgery Can be done in conjunction with Diamox challenge test ICP <10 mm Hg is normal Severe or uncontrolled when ICP>40 mm Hg for >15 minutes A waves or plateau waves Large increases above baseline to max 50-100 mm Hg for 5-20 min Associated with ICP>20 & with neurological symptoms related to pressure As baseline ICP increases, A waves increase in magnitude & frequency Indicate intracranial spatial compensation has been exhausted Associated with increased cerebral blood volume and decreased cerebral blood flow B waves Rhythmic oscillations about every minute with amplitude max of 50 mm Hg Partly related to depression of consciousness Often found in association with periodic breathing May disappear with mechanical ventilation C waves Rhythmic oscillations up to 20 mm Hg with frequency of 4-8/minute Associated with Traube-Herring-Mayer blood pressure waves. A waves important, B & C waves of little usefulness in patient management. Lumbar infusion tests +/- computer modeling Measures of resistance or conductance Mixed results in predicting outcome CONCLUSIONS Shunt responsiveness (50-70 % accuracy) short history known cause of hydrocephalus predominance of gait disorders CT showing hydrocephalus A waves & excess B waves Shunt unresponsiveness Predominantly demented Substantial cortical atrophy Extensive white matter involvement When doubts persist after clinical, CT, MRI & tap test; perform lumbar drainage and to shunt only if unequivocal clinical improvement. Therapeutic nihilism vs shunt every patient: which is best test? N=166 consecutive patients with clinical & CT criteria shunted 36% overall improvement 21% substantial improvement Acute complication rate post shunt: 28% Death or severe residual morbidity 7% Cumulative complication rate post shunt: 5%/yr Conclusion: more harm than good is done by subjecting most NPH patients to a shunt procedure. Vanneste J et al Shunting normal pressure hydrocephalus: Do the benefits outweigh the risks? A multicentre study and literature review. Neurology 1992; 42:55-59. |
