A total of 10 studies (n=342) were included in the review. Six observational studies were included in the review of effectiveness (258 patients with implanted IDDS).
In terms of quality, no randomised controlled trials (RCTs) were included in the review. All 6 studies included in the assessment of effectiveness were observational, and four had no comparison group.
All 6 studies of pain reported improved mean pain ratings in patients implanted with a permanent IDDS: the mean pain intensity score on a 0-to-100 scale was 82 pre-IDDS (3 studies) versus 45 at 6 months (3 studies) and 44 at 12 months (2 studies). Assuming patients lost to follow-up were failures, the proportions of patients reporting a 50% or more pain reduction were 30%, 38% and 56% at 6 months in 3 studies, and 44% after a mean follow-up of 29 months (1 study).
The authors stated that while all 6 studies reported some improvement in patient physical functioning with the IDDS, all the studies had major methodological flaws including the use of unvalidated measures, lack of reporting of relevant statistics, and high attrition rates.
There were 10 studies of complications. The percentages reported are weighted means. The most commonly reported drug-related adverse events were nausea/vomiting (33%; 3 studies), urinary retention (24%; 4 studies) and pruritus (26%; 3 studies). Non drug-related biologic complications included wound infection (12%; 3 studies), meningitis (2%; 3 studies) and pump malposition (17%; 2 studies). Hardware complications were common in the 2 studies that reported them and included catheter-related complications (18%; 2 studies), catheter migration/dislodgement (12%), catheter obstruction/occlusion (19%) and mechanical failure (5%). Surgery for revision of equipment was required in 27% (range: 13 to 39; 4 studies), and 5% of patients (range: 0 to 27; 7 studies) required permanent removal of the IDDS.
The review also reports less common serious adverse events.