The authors of a study showing the potential value of ultrasound-guided stem cells as a standard treatment for stress urinary incontinence need to be commended on their results.
The authors, from the University of Innsbruck in Austria, showed that 38 of 42 women injected with autologous cells were completely continent at 12 months, compared with two of 21 patients who received conventional treatment with endoscopic injections of collagen (see, "Stem cells may restore continence in both sexes", and Lancet 2007; 369:2179-86). In addition, mean thickness of the rhabdosphincter increased from a baseline of 2.13 mm in all patients to 3.38 mm for patients treated with the autologous cells and 2.32 mm in those treated with collagen (p<.0001).
These findings, while very encouraging, raise two critical questions.
Why the authors decided to inject both urethral layers is unclear, and the mechanism of improvement associated with the submucosal fibroblast or myoblast injections into the rhabdosphincter is unknown.
Second, would other bulking materials injected under ultrasound guidance yield similar results? The ultrasound-guided urethral injections appear to be superior to routine transurethral injections. Ultrasound-guided injection allows a precise deposit of the bulking material, offering a greater advantage.
It would be interesting to determine whether injecting other, less-expensive materials, such as calcium hydroxylapatite (Coaptite), pyrolytic carbon-coated beads (Durasphere), or silicone particles (all of which are not quickly reabsorbed like collagen) under ultrasound guidance would yield results similar to those seen with the stem cell injections. I suspect that the results would not be significantly different.
It is worth noting that the cost of preparing stem cells in a single patient is more than $15,000, while an injection of calcium hydroxylapatite is $400. We need to know if stem cells are, indeed, cost effective.
In summary, we don't yet have clear evidence that the very positive results shown with the use of stem cell injections constitute true urethral regeneration, which would be a great advance, or a better, more precise injection of a good bulking agent.
Certainly, longer follow-up and multicenter trials are needed to answer these important questions.
Dr. Raz, a member of the Urology Times Editorial Council, is professor of surgery/urology, UCLA School of Medicine, Los Angeles.