Fibromyalgia is thought to be caused by inflammation of the nervous system, triggering pain. Animal studies have shown that probiotics can reduce nervous system hypersensitivity.
A vegan diet has shown much promise in alleviating symptoms in fibromyalgia. The abundant prebiotic content of a vegan diet may be one reason. A Mediterranean diet or fasting did not change intestinal flora however.
Finding definitive evidence for probiotic use in this painful disorder will be welcomed.
Further reading on fibromyalgia and probiotics:
Vegan diet alleviates fibromyalgia symptoms.
Fibromyalgia syndrome improved using a mostly raw vegetarian diet: an observational study.