A Phase II trial giving an anti-cancer drug to sufferers of chronic fatigue syndrome (CFS) has produced encouraging, if puzzling, results. Two-thirds of the patients in the small trial showed dramatic but delayed responses, while one-third gained little benefit from the treatment.

CFS is a particularly hard condition to diagnose, let alone treat. Having once been dismissed as psychosomatic, there is now medical acceptance that it has a biological cause, but not much agreement on what that is.

Moreover, apart from the debilitating lack of energy, the symptoms are so vague that many people with other conditions have probably been placed in the CFS basket, if indeed it is really one disease rather than several.

This confusion makes it particularly hard to find treatments. Programs that work for some people show no success for others. Nevertheless, a trial conducted at Haukeland University Hospital in Bergen, Norway, and reported in PloS One could be the most promising development so far.

In 2004, Dr. Øystein Fluge and Professor Olav Mella were treating lymphoma in a patient who also had CFS. To their surprise, the individual's CFS got better. While this could easily have been a coincidence, Fluge and Mella conducted a trial of 30 people with CFS, half of whom were given the same drug, Rituximab, as the original patient, while the other half received a placebo.

Two-thirds of the patients given Rituximab showed significant improvement relative to the control group, while one-third did not.

Now, Fluge and Mella have extended the trial to see if the benefits last, while also giving Rituximab to most of those who were originally on the placebo. Of the 29 in the combined group, 18 patients – labeled "responders" – reported clinically significant benefits, 14 of them dramatically so. Even some “non-responders” showed signs of benefits much later in the treatment.

“Eleven of the 18 responders were still in remission three years after beginning the treatment, and some have now had no symptoms for five years,” Fluge told New Scientist. “Suddenly, their limbs started to work again and their hands were no longer cold or sweaty.”

^{0 represents major worsening in fatigue, 6 major improvement. Right graph, average scores of responders and non-responders. Credit Fluge et al., PLoS One}

Despite the benefits, Rituximab is no miracle cure. For one thing, it takes 4-6 months to even start working, and many responders took almost two years to show the full benefits, a delay the authors attribute to the time taken for the drug to clear disease-triggering antibodies from patients. 

Moreover, Rituximab has known side effects, including increased vulnerability to viral infections and, in extreme cases, cardiac arrest. On the other hand, as a destroyer of B cells, Rituximab is used to treat not just lymphomas but also autoimmune diseases and transplant rejections, so there is an extensive body of evidence on when it can be applied safely.

The study relied on patients' self-description of their levels of fatigue, and one patient described their condition as significantly worse throughout the treatment. However, with seven of the patients initially being partially or mainly bedridden, and even the milder cases severely debilitated, the benefits were often transformative.