Does it make sense to look for parasites in RAP?

Probably not, in the absence of other symptoms.  A small study from Switzerland shows that treatment of Blastocystis hominis does not help recurrent abdominal pain (RAP) more than placebo (JPGN 2012; 54: 677-79).

This study result is not surprising.  A previous study of 157 RAP pediatric patients (JPGN 2007; 44: 524-26) showed that testing for ova and parasites was unnecessary as the incidence of parasitic infections in this population was not increased in RAP patients compared with controls. In this 2007 study, stool samples were positive for parasitic infection in 15 children, with no difference in prevalence between children with chronic abdominal pain (6/87; 7%) and healthy control children (9/70; 13%).

The current study had 37 patients complete the study.  The pain index (PI) for all patients improved in the study; however, there was no difference between patients who received antibiotics (trimethoprim-sulfa was used as first-line agent) compared to those who received placebo.

Regarding the methodology, the PI was either a visual analog scale with numbers from 0 to 10 or a standardized face scale; the specific scale was determined by the patient age.  Also, among the 20 patients who received antibiotics, 13 continued with B hominis in their stool tests after an initial round of therapy.  Yet the change in pain was virtually identical.  In antibiotic-treated patients, initial PI was 7.1.  After treatment, those with persistent B hominis detected in the stool had a PI of 4.2 whereas those with negative stool specimens had a PI of 4.1.  The placebo patients started with a PI of 7.4; after placebo treatment, a similar proportion cleared the B hominis from their stool –in this group, at the conclusion of the placebo treatment the PI was 2.4; the placebo group with persistent detection of B hominis had a PI of 3.2 at the conclusion of the study.

Although the potential pathogenicity of B hominis in humans remains unclear, it is not unusual in clinical practice for patients with this finding to receive treatment.   Besides trimethoprim-sulfa, metronidazole is frequently administered. Based on this study, placebo would be as helpful as an antibiotic in improving clinical symptoms.

Related blog entries:

What to make of FODMAPs

Pain changes brain