Rheumatoid arthritis (RA) is a highly complex inflammatory autoimmune disease. Several drugs have been developed in recent decades to target the immune components of inflammation. However, even with effective anti-inflammatory and immunosuppressive therapies for controlling RA, many patients still report significant levels of chronic pain due to CNS neuroplasticity, perpetuating physical disability, psychosocial problems, decreased work activity, and poor quality of life. In addition, chronic pain can lead to increased public spending due to the need for more medical visits, ineffective drug treatments, and financial disability benefits. Transcranial stimulation (a noninvasive neural stimulation technique with minimal adverse effects and easy home use) has been a promising adjunct tool in the treatment of chronic pain and psychological disorders in diseases that affect the central nervous system in the long term. Thus, exploring transcranial direct current stimulation in RA patients with low levels of inflammation could impact on improving pain, functionality, psychological aspects and overall quality of life, as well as reducing healthcare costs for society.

Rheumatoid arthritis (RA) is a highly complex inflammatory autoimmune disease. Several drugs have been developed in recent decades to target the immune components of inflammation. However, even with effective anti-inflammatory and immunosuppressive therapies for controlling RA, many patients still report significant levels of chronic pain due to CNS neuroplasticity, perpetuating physical disability, psychosocial problems, decreased work activity, and poor quality of life. In addition, chronic pain can lead to increased public spending due to the need for more medical visits, ineffective drug treatments, and financial disability benefits. Transcranial stimulation (a noninvasive neural stimulation technique with minimal adverse effects and easy home use) has been a promising adjunct tool in the treatment of chronic pain and psychological disorders in diseases that affect the central nervous system in the long term. Thus, exploring transcranial direct current stimulation in RA patients with low levels of inflammation could impact on improving pain, functionality, psychological aspects and overall quality of life, as well as reducing healthcare costs for society.

Inclusion Criteria:

• Participants aged 18-70 with RA.
• Participants with generalized pain ≥ 40 mm on the VAS-Pain scale, lasting over 3 months, and not of mechanical or inflammatory origin, as assessed by a certified rheumatologist.
• Evidence of low inflammatory markers, including with C-reactive protein (CRP) <10 mg/dL and sedimentation rate (ESR) <20 mm/h, and stable treatment for PsA for at least 6 months prior to study enrollment.

Exclusion Criteria:

• History of brain surgery, traumatic brain injury, stroke, previous intracranial metal implantation, pregnancy, or breastfeeding.
• Previous history of autoimmune diseases other than RA.
• History of neurological diseases.
• Previous history of neoplasia.
• History of any other uncompensated clinical disease.
• Use of illicit drugs within the past 6 months.

The Individual Patient Data (IPD) will not be shared due to privacy and confidentiality concerns, as well as the protection of sensitive patient information. Additionally, there may be legal or regulatory restrictions that prevent the release of such data. Sharing of IPD could also raise ethical issues regarding informed consent and the use of data beyond the initial scope of the study.