1 Department of Radiology, School of Para-Medicine, Hormozgan University of Medical Sciences (HUMS), Bandar Abbas, Iran.
2 Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences (TUMS), Tehran, Iran.
3 PERFORM Preventive Medicine and Health Care Centre, Concordia University, Montreal, Quebec, Canada.
4 Department of Sports Medicine, School of Medicine, Tehran University of Medical Sciences (TUMS), Tehran, Iran.
5 Spine Center of Excellence, Yas Hospital, Tehran University of Medical Sciences, Tehran, Iran.
6 Department of Neurosurgery, Shariati hospital, Tehran University of Medical Sciences, Tehran, Iran.
7 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences (TUMS), Tehran, Iran.
8 Department of Radiology, School of Medicine, Tehran University of Medical Sciences (TUMS), Tehran, Iran.

Background: Non-specific chronic low back pain (CLBP) is a common painful condition and is responsible for different physical disorders. Despite alternative therapies, patients still suffer from persistent pain. Repetitive transcranial magnetic stimulation (rTMS) has provided much evidence of pain reduction, but results have not been examined deeply in CLBP symptoms.

Objective: The analgesic effect of rTMS in non-specific CLBP patients was evaluated by the amplitude of low-frequency fluctuation (ALFF) analysis in resting-state fMRI.

Material and methods: In this experimental study, fifteen non-specific CLBP participants (46.87±10.89 years) received 20 Hz rTMS over the motor cortex. The pain intensity and brain functional scan were obtained during pre and post-stimulation for all participants. The ALFF maps of the brain in two scan sessions were identified and the percentage of pain reduction (PPR%) was determined using paired t-test. Also, correlation analysis was used to find a relationship between ALFFs and pain intensity.

Results: Pain intensity was significantly reduced after induced-rTMS in non-specific CLBP (36.22%±13.28, P<0.05). Positive correlation was found between ALFF in the insula (INS) and pain intensity (r_pre-rTMS=0.59, r_post-rTMS=0.58) while ALFF in medial prefrontal cortex (mPFC) and pain intensity had negatively correlated (r_pre-rTMS=-0.54, r_post-rTMS=-0.56) (P<0.05). ALFF increased in mPFC while INS, thalamus (THA), and supplementary motor area (SMA) showed decremental ALFF followed by rTMS.

Conclusion: This study demonstrated that ALFF in INS, THA, mPFC, and SMA is associated with CLBP symptoms and analgesic effects of rTMS. ALFF potentially seems to be a proper objective neuroimaging parameter to link spontaneous brain activity with pain intensity in non-specific CLBP patients.