Small bowel bacterial overgrowth and lactose intolerance during radical pelvic radiotherapy: An observational study

Loose stool affects up to 80% of all patients during pelvic radiotherapy and faecal incontinence may occur. Several causes for diarrhoea have been defined, though few oncologists target these causes in affected patients and most treat symptomatically only. It is not known whether small bowel bacterial overgrowth, a frequent cause of gastrointestinal symptoms in other contexts, occurs during radiotherapy. The frequency of new-onset lactose intolerance during pelvic radiotherapy is also not clear.

To perform an observational pilot study to estimate the incidence of small bowel bacterial overgrowth and lactose intolerance during radical pelvic radiotherapy. Before treatment started and at weeks 4-5 of pelvic radiotherapy, a glucose hydrogen breath test and lactose tolerance test were performed. Gastrointestinal symptoms were assessed using the Vaizey incontinence questionnaire and the Radiation Therapy Oncology Group scoring system.

Twenty two men and 17 women (median age 61, range 42-81) were recruited, four were treated for gastrointestinal, 17 were treated for gynaecological and 18 for urological cancers. Thirty-eight patients underwent glucose hydrogen breath tests and 26 patients underwent lactose breath tests at both time points. Ten patients (26%) were positive for the glucose hydrogen breath test: 60% of these developed new or worsening faecal incontinence during treatment and 60% had worsening bowel frequency. Four patients (15%) developed lactose intolerance. Of these 1 developed worsening faecal incontinence during treatment, 2 (50%) developed new-onset increase in bowel frequency or a change in the quality of bowel habit.

Small bowel bacterial overgrowth and lactose intolerance may occur during radical pelvic radiotherapy and are likely to contribute to gastrointestinal symptoms in some patients.