title: Impact of duration of symptoms on CSF dynamics in idiopathic normal pressure hydrocephalus.
abstract: OBJECTIVE
  Cerebrospinal fluid (CSF) pressure-volume compensation may change over time as part of normal ageing, where the resistance to CSF outflow increases and the formation of CSF decreases with age. Is CSF compensation dependent on duration of symptoms in idiopathic normal pressure hydrocephalus (iNPH)?
  
  
  METHODS
  We investigated 92 patients presenting with iNPH. Mean age was 73 (range 47-86). There were 60 men and 32 women. They all presented with gait disturbance and ventricular dilatation. Memory deficit occurred in 72% and urinary incontinence in 52% of patients. All patients underwent computerized CSF infusion tests. Sixty-four shunted patients were available for follow-up, and their improvement was expressed using the NPH score.
  
  
  RESULTS
  Mean intracranial pressure (ICP) was 10.1±5.1 mmHg, and mean resistance to CSF outflow was 17.3±5.2 mmHg/(ml/min). Mean duration of symptoms was 24±19 months (range from 2 weeks to 86 months). Baseline ICP, magnitude of ICP pulse waveform, brain compliance and improvement after shunting (72% of patients improved) did not exhibit any dependency on the duration of symptoms. The resistance to CSF outflow showed a strong tendency to decrease in time with the duration of symptoms beyond 2 years (R= -0.702; P<0.005).
  
  
  CONCLUSIONS
  This is a preliminary observation, and it suggests that for patients with duration of symptoms longer than 2-3 years, the threshold for normal resistance to CSF outflow should be duration-adjusted.
authors.affiliation: Neurosurgical Unit, Department of Clinical Neurosciences, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK. Mc141@medschl.cam.ac.uk
authors.forename: Z
authors.initials: Z
authors.lastname: Czosnyka
authors.forename: B
authors.initials: B
authors.lastname: Owler
authors.forename: N
authors.initials: N
authors.lastname: Keong
authors.forename: T
authors.initials: T
authors.lastname: Santarius
authors.forename: O
authors.initials: O
authors.lastname: Baledent
authors.forename: J D
authors.initials: JD
authors.lastname: Pickard
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002552:Cerebral Ventricles / Q000473:pathology / Q000503:physiopathology*; D002555:Cerebrospinal Fluid / Q000502:physiology*; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology*; D005260:Female; D006801:Humans; D006850:Hydrocephalus, Normal Pressure / Q000453:epidemiology* / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D016896:Treatment Outcome