Post-polio syndrome (PPS) is a neurological disorder that may first appear years after an acute polio infection. In addition to worsening weakness and fatigue, pain, depression, cold intolerance, and sleep disturbances also may occur. Although polio vaccines have drastically decreased the incidence of new cases of polio in industrialized countries, new cases still occur in areas of Asia and Africa. As polio survivors age, PPS symptoms emerge, even in people who have been stable for 15 years or more. The cause of PPS still remains elusive, and there are no definitive treatment options.
The study enrolled 32 patients who had contracted polio at a mean age of 31 months, but then were stable clinically for an average of 55 years. They were referred to a national reference center, the Physical Rehabilitation Medicine Unit at Malcesine Hospital in Verona, Italy, for the treatment of PPS after complaining of progressively worsening weakness and fatigue. Half of the patients were randomly assigned to receive anodal tDCS applied bilaterally to the premotor cortex every day, 5 days a week, for three weeks. The control group received current for 5 seconds (sham tDCS). In preliminary testing, subjects said they could not distinguish between real and sham tDCS.
Patients underwent a battery of tests at baseline and then three weeks later. The tests looked at quality of life, multiple aspects of fatigue, depression, and sleep quality.
The authors found that tDCS treated patients improved more than sham-treated patients on several measures of a patient health survey (the Short Form Health Survey or SF-36), including physical functioning, role limitations due to physical health, vitality, social functioning and role limitations due to emotional health. No significant differences were found between the groups on questions related to bodily pain, general health, or mental health.
One of the most noticeable effects of tDCS treatment was an improvement in sleep quality. Scores on the Pittsburgh Sleep Quality Index (PSQI) decreased 65% compared to 25% in the control group, a significant difference (p<0.05). Significant correlations were found between PSQI scores and physical functioning, social functioning, and emotional health. Interestingly, sleep quality improved more in patients who were younger when poliomyelitis developed.
Whether tDCS relieves fatigue directly is still unclear. While fatigue-related sub-items of the SF-36 improved after tDCS, no significant changes were found using specific fatigue-assessment tests such as the Piper Fatigue Scale or the Fatigue Severity Scale. No changes were noted between groups in depression scores.
"tDCS might work by improving sleep. Because changes in sleep quality affect physical and psychological states, improving sleep quality could improve perceived vitality, social and emotional functioning, and, indirectly, also fatigue," says lead investigator Laura Bertolasi, MD, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, Italy. "tDCS effects on sleep fit in with results in healthy subjects, fibromyalgia, and schizophrenia."