Disease Activity in Rheumatoid Arthritis and Systemic Lupus Erythematosus and Its Relation to Muscle Performance,Fatigue and Blood Parameters

Rheumatoid arthritis (RA) is the most common inflammatory arthritis, affecting 0.5-1% of the general population world-wide. It is primarily a disease of the joints, but abnormal systemic immune responses are evident and cause a variety of extra-articular manifestations .

Physical inactivity is one of the key mechanisms affecting skeletal muscle mass and body composition, leading to progressive muscle loss and abdominal fat gain . Muscle strength and endurance are determinants of muscle performance. Relatively little is known about how muscle performance relates to RA clinical variables; also muscle performance is not routinely assessed in clinical practice among patients with RA. Decreased muscle strength has negative outcomes in RA, associating with disease activity, radiological damage and disability .Rheumatoid cachexia, including loss of muscle mass and concomitant increase in fat mass with normal or increased body weight , is a common feature in patients with RA. Assessment of inflammation in RA with markers is important to detect long-term outcome. Parameters of hemogram, particularly those including immune system elements, are important in the assessment of different diseases and/or signs. Immune system elements involve the neutrophils, lymphocytes and platelets that have a role in the control of inflammation, while also undergoing changes secondary to inflammation .

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with chronic relapsing-remitting course and variable manifestations varying from mild mucocutaneous to severe, life-threatening illness .

It has been speculated that fatigue, a symptom frequently observed in approximately 80% of SLE patients , may contribute to a reduction in physical fitness (i.e.,muscle weakness and low cardiovascular capacity) which, in turn, leads to an impairment in the performance of activities of daily living and in the overall quality of life .

SLE patients experienced decreased physical function, low dynamic muscle strength capacity, and poor quality of life, suggesting that either "residual" fatigue or other factors (e.g., long-term medication or systemic inflammation) may have contributed to the poor health-related findings .