Patients with chronic fatigue syndrome (CFS) complain of long-lasting fatigue and pain which are not relieved by rest and worsened by physical exertion. Previous research has implicated metaboreceptors of muscles to play an important role for chronic fatigue and pain. Therefore, we hypothesized that blocking impulse input from deep tissues with intramuscular lidocaine injections would improve not only the pain but also fatigue of CFS patients.
In a double-blind, placebo-controlled study, 58 CFS patients received 20 mL of 1% lidocaine (200 mg) or normal saline once into both trapezius and gluteal muscles. Study outcomes included clinical fatigue and pain, depression, and anxiety. In addition, mechanical and heat hyperalgesia were assessed and serum levels of lidocaine were obtained after the injections.
Fatigue ratings of CFS patients decreased significantly more after lidocaine compared to saline injections ( p = 0.03). In contrast, muscle injections reduced pain, depression, and anxiety ( p < 0.001), but these changes were not statistically different between lidocaine and saline ( p > 0.05). Lidocaine injections increased mechanical pain thresholds of CFS patients ( p = 0.04) but did not affect their heat hyperalgesia. Importantly, mood changes or lidocaine serum levels did not significantly predict fatigue reductions.
These results demonstrate that lidocaine injections reduce clinical fatigue of CFS patients significantly more than placebo, suggesting an important role of peripheral tissues for chronic fatigue. Future investigations will be necessary to evaluate the clinical benefits of such interventions.