Objectives: A rapid and early loss of skeletal muscle mass underlies the physical disability common amongst survivors of critical illness. However, skeletal muscle function depends not only on its quantity but its quality, which may be adversely affected. We set out to characterise the changes in macroscopic muscle echogenicity and fascial characteristics that occur early in critical illness, and to relate these to microscopic histologically defined myofibre necrosis and fascial pathology.
Design and setting: Prospective two center observational study.
Patients: Thirty subjects comprising a subgroup of patients recruited to the Musculoskeletal Ultrasound in Critical Illness: Longitudinal Evaluation (MUSCLE) study.
Measurements and main results: Comparisons were made between sequential Vastus Lateralis histological specimens and ultrasound assessment of Rectus Femoris echogenicity. Change in muscle echogenicity was greater in patients who developed muscle necrosis (n = 15) than in those who did not (8.2% [95% CI, -5.3 to 21.7] vs -15.0% [95% CI, -28.9 to -1.09]; p = 0.016). The area under receiver operator curve for ultrasound echogenicity's prediction of myofiber necrosis was 0.74 (95% CI, 0.565 to 0.919; p = 0.024) increasing to 0.85 (95% CI, 0.703 to -0.995; p = 0.003) with the removal of those with potential iatrogenic muscle damage. Fasciitis was observed in 18 of 30 biopsies (60%).
Conclusions: Myofiber necrosis and fascial inflammation can be detected noninvasively using ultrasound in the critically ill. Fasciitis precedes and frequently accompanies muscle necrosis. These findings may have functional implications for survivors of critical illness.