Muscle function in rheumatic disease patients treated with corticosteroids.

Area of Science:

• Rheumatology
• Muscle Physiology
• Pharmacology

Background:

• Long-term corticosteroid therapy is known to cause muscle fiber atrophy, specifically affecting type 2 fibers.
• Rheumatic diseases often require prolonged corticosteroid treatment, potentially impacting muscle function.

Purpose of the Study:

• To characterize and quantify muscle function deficits in patients with rheumatic diseases on long-term corticosteroid therapy.
• To assess the impact of corticosteroids on quadriceps peak torque and power.

Main Methods:

• Utilized an isokinetic dynamometer (Cybex II) to measure quadriceps function (peak torque, power) in patients and controls.
• Performed measurements during four constant velocity movements to analyze power-velocity relationships.
• Included 19 patients with rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus) and 11 healthy controls.

Main Results:

• Patients on long-term corticosteroids demonstrated significantly lower muscle power across all tested speeds compared to controls.
• The deficit in power production increased at higher speeds, evidenced by differing power-velocity regression slopes.
• Peak torque measurements were not consistently effective in differentiating between patient and control groups.

Conclusions:

• Patients with rheumatic diseases undergoing long-term corticosteroid treatment exhibit a reduced capacity for muscle power generation.
• The described methodology enables the quantitative assessment of these muscle power deficits in a clinical context.
• Impaired muscle power is a significant functional consequence of corticosteroid therapy in this patient population.