Using smaller microspheres does not improve PAE outcomes

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microspheres
Tiago Bilhim

Prostate artery embolization (PAE) outcomes do not differ significantly when microspheres of different sizes are used as embolic agents, a recent single centre, randomised controlled clinical trial reports. Writing in the Journal of Vascular and Interventional Radiology (JVIR), the authors report no differences between the clinical success rates using 100µm- to 300µm-sized particles at 18 months, although the incidence of minor self-limiting complications such as dysuria was greater with smaller particles.

“Particle sizes used for PAE range between 50µm and 300µm for non-spherical polyvinyl alcohol (PVA) particles and between 100µm and 500µm for spherical embolic agents. The best size with which to obtain optimal clinical success is not known”, senior author Tiago Bilhim, lead author Daniel Torres (both Hospital Saint Louis, Lisbon, Portugal) and colleagues write.

Therefore, they set out to investigate the safety and efficacy of PAE using trisacryl gelatine microspheres of different sizes for the treatment of benign prostatic hyperplasia (BPH).

The study authors randomised 138 patients who underwent PAE for BPH between July 2015 and December 2016 to one of three groups: A, B and C. Embolization was performed using microspheres of different sizes in each group: in group A, the microspheres used were 100–300µm; for group B, 300–500µm microspheres were used; and in group C, patients were first embolized with 100–300µm microspheres before being embolized with 300–500µm microspheres. All patients were evaluated before the procedure, and one, three, six, 12, and 18 months after PAE.

At baseline, the International Prostate Symptom Score (IPSS), quality of life scores, and prostate volume were comparable across all three groups (p>0.05). In group A, these were 23, 4.14, and 87.9cm3, respectively; for group B: 23, 4.09 and 89cm3; in group C: 24.2, 4.29 and 81cm3.

After PAE, the scores and data were:

  • Group A: 9.98, 2.49 and 65.1cm3 (p=0.23)
  • Group B: 8.24, 2.26 and 63.1cm3 (p=0.39)
  • Group C: 10.1, 2.69 and 53.1cm3 (p=0.24)

Specifically comparing groups A and B—patients embolized with 100–300µm microspheres versus patients embolized with 300–500µm microspheres—the authors report no statistically significant differences in IPSS, quality of life or prostate volume. Detailing their results, Bilhim, Torres et al write: “The patients in whom the smaller particle size was used showed a significant regrowth in prostate size from three to 12 months, and there was an increase in minor adverse events in patients who underwent PAE with smaller microspheres, although this was not statistically significant.”

Indeed, the study investigators conclude that PAE using larger particles may be better, as there is a higher rate of minor adverse events when 100–300µm microspheres are used as embolic agents. When a combination of microsphere sizes is used, as in group C, no benefit was seen compared to either groups A or B, and, compared with the 300–500µm cohort, there was a higher rate of adverse events.

Bilhim, Torres and colleagues postulate that, as the number of minor adverse events was significantly lower in group B, the only study arm not to include 100–300µm microspheres, the smaller sized particles were the culprit. They explain that the smaller sized microspheres “could penetrate more distally, causing more inflammation and necrosis”.

Drawing the reader’s attention to previous studies that have found an advantage to using smaller sized embolic agents (“The use of smaller PVA particle sizes led to greater prostate ischaemia, greater prostate volume reduction, and greater clinical improvement, without a higher rate of adverse events. Retrospective analysis looking at spherical embolic agents has also shown that spherical embolic agents <300µm performed best”), the authors note that this potential benefit has to be counterbalanced by the potentially higher rate of adverse events and ejaculation disorders that they say has been “overlooked” in most PAE studies.

All adverse events were mild and self-limited, with the following rates (p<0.001):

  • Group A: 86% (37 of 43)
  • Group B: 41.3% (19 of 46)
  • Group C: 58.3% (28 of 48)

Dysuria was the most frequent adverse event, occurring in 20.4% (28 of 137) of patients.


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