Risk Factors to the Upper Tract Damage in SCI 

Increased intravesical pressure: Pandora’s Box

  • Increased intravesical pressure is commonly observed in the SCI/D with bladder dysfunction.
  • Increased intravesical pressure is the most important key factor in the pathogenesis of the hydronephrosis and VUR, which are in close connection to the renal deterioration.

History of the Pressure-based Concept in Managing SCI/D

(insertion of the picture: title of an article authored by Dr McGuire)

  • In 1981, McGuire and coworker first described the linkage between the intravesical pressure and renal damage and formally characterized and conceptualized the ‘detrusor leak point pressure (DLPP)’ [McGuire 1981]. This is a monumental finding in the urodynamic history. The American Urological Association recognized this as one of the ‘classic’ findings in urology in the last 100 years [McGuire 2002]. He found a striking association between intravesical pressures > 40cmH2 O and the presence of reflux in myelodysplasia patients with neuropathic bladders [McGuire 1981; McGuire 1996].
    • Analysis of the clinical progress and urodynamic study results of 42 myelodysplastic patients followed for a mean of 7.1 years.
    • No patient with the intravesical pressure ≤ 40cmH2O at the time of urethral leakage (low DLPP group) had VUR.
    • 68% of the patients with the intravesical pressure > 40cmH2O (high DLPP group) showed VUR.
  • Subsequently, this McGuire’s concept in the pathogenesis of renal damage in neurogenic bladder was confirmed by many urologists.
    • Myelodysplastic newborns with DSD or high pressure, reduced-compliance bladders are at high risk of having upper urinary tract changes and require preventive decompressive treatment [Sidi 1986]
    • Meningomyelocele patients with evidence of upper tract deterioration had lower bladder compliance and higher leak pressure than patients with normal kidneys [Ghoniem 1990]
    • Urodynamic features of high leak pressure and DSD in myelodysplasia have been associated with an increased risk. Scoring system from 5 objective urodynamic parameters, including bladder compliance, hyperreflexia, dyssynergia, outlet resistance, and VUR was developed to make management decision in myelodysplasia [Galloway 1991]
  • This concept has gradually been applied to any neurogenic condition. Thanks to this concept, decreasing intravesical pressure became the most important target for the treatment of neurogenic bladder.
    • Maintaining the pressure at typical capacity at less than 40cmH2O is associated with increased spontaneous resolution of vesicoureteral reflux and a lower incidence of upper tract deterioration. [Flood 1994]
    • A pressure-based management program for the patients with neurogenic bladder secondary to myelodysplasia was instituted about 40% of myelodysplastic children are at high risk for the development of upper tract changes [Wang 1988]
    • After urethral dilation in the patients with myelodysplasia, intravesical pressures decreased, and upper tract function and measured bladder compliance improved [Wang 1989]. This latter observation led to the recognition that it is largely the outlet which controls bladder pressure. The bladder seems genetically programmed to empty. Anything that interferes with emptying leads to compensatory bladder responses: which include an increase in the size of the individual detrusor muscle fibers, a change in receptor activity and elevated detrusor pressures at smaller and smaller volumes. One can ameliorate these changes with frequent intermittent catheterization various drugs to prolong bladder storage function, and or a decrease in outlet resistance which maintains a low bladder pressure by inducing low pressure leakage. That effect is also associated with a complete resolution of the compliance changes in the bladder and also the morphologic changes associated with muscular hypertrophy.
  • Subsequently, McGuire’s concept is generalized to the all forms of neurogenic bladder and non-neurogenic neurogenic bladder [Wheeler 1993; Noll 1995]
  • This concept changed basic pattern of clinical decision making: When medical management is unsuccessful in correcting abnormal bladder dynamics (regardless of cause) and resolving secondary reflux, enterocystoplasty, vesicostomy, or some other form of urinary diversion becomes a necessary option in management.

Major Risk Factors to the Upper Tract Damage in SCI/D

  • Basic decision making in the management of SCI patient is based on the concept of intravesical pressure since increased intravesical pressure is the most important risk factor in the upper tract damage.
  • Secondary factors contributing to or related to this pressure are schematically drawn.
    • Detrusor hyperreflexia
    • Bladder compliance
    • DSD
    • Increased outlet resistance
    • VUR
  • These risk factors can be accurately identified using modern urodynamic studies. This explains why the urodynamic findings are so important in the initial diagnosis and long term followup of these conditions.
Key Points of This Section
  • The most treatable abnormality in neuropathic lower urinary tract dysfunction is detrusor pressure. Provided measured detrusor pressure is kept within narrow limits long term risks are minimized.
  • A common treatment focus in neuropathic bladder dysfunction is bacteriuria- which in these cases is rarely, if ever, the sole cause of any symptom or complication. The combination of elevated pressures and chronic bacteruiria, almost universal in these conditions, is where trouble begins.
  • Unfortunately treatment of “infection” is never associated with eradication of bacteriuria, and without treatment of elevated detrusor pressures it is futile. More to the point, with control of detrusor pressures, treatment of chronic bacteriuria is not necessary.

References

  • Flood HD, Ritchey ML, Bloom DA, Huang C, McGuire EJ. Outcome of reflux in children with myelodysplasia managed by bladder pressure monitoring. J Urol. 1994 Nov;152(5 Pt 1):1574-7.
  • Galloway NT, Mekras JA, Helms M, Webster GD. An objective score to predict upper tract deterioration in myelodysplasia. J Urol. 1991 Mar;145(3):535-7.
  • Ghoniem GM, Roach MB, Lewis VH, Harmon EP. The value of leak pressure and bladder compliance in the urodynamic evaluation of meningomyelocele patients. J Urol. 1990 Dec;144(6):1440-2.
  • McGuire EJ, Woodside JR, Borden TA, Weiss RM. Prognostic value of urodynamic testing in myelodysplastic patients. 1981. J Urol. 2002 Feb;167(2 Pt 2):1049-53.
  • McGuire EJ, Woodside JR, Borden TA, Weiss RM. Prognostic value of urodynamic testing in myelodysplastic patients. J Urol. 1981 Aug;126(2):205-9.
  • McGuire EJ, Cespedes RD, O'Connell HE. Leak-point pressures. Urol Clin North Am. 1996 May;23(2):253-62.
  • Noll F, Sauerwein D, Stohrer M. Transurethral sphincterotomy in quadriplegic patients: long-term-follow-up.Neurourol Urodyn. 1995;14(4):351-8.
  • Sidi AA, Dykstra DD, Gonzalez R. The value of urodynamic testing in the management of neonates with myelodysplasia: a prospective study. J Urol. 1986 Jan;135(1):90-3.
  • Wang SC, McGuire EJ, Bloom DA. A bladder pressure management system for myelodysplasia--clinical outcome. J Urol. 1988 Dec;140(6):1499-502.
  • Wang SC, McGuire EJ, Bloom DA. Urethral dilation in the management of urological complications of myelodysplasia. J Urol. 1989 Oct;142(4):1054-5.
  • Wheeler JS Jr, Walter JW. Acute urologic management of the patient with spinal cord injury. Initial hospitalization. Urol Clin North Am. 1993 Aug;20(3):403-11.

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