ICU-Acquired Weakness: Diagnostic Yield of a Clinical Diagnosis with Additional Quantification of Myosin Loss in Adult Critically Ill Patients.

Background/Objectives: Intensive care unit acquired weakness (ICUAW) is common in critically ill patients. However, ICUAW is an umbrella term for multiple neuromuscular pathologies, including critical illness myopathy (CIM). This study aimed to evaluate the diagnostic yield of the clinical diagnosis of ICUAW compared with that of preferential myosin loss, i.e., the hallmark of CIM. Methods: Critically ill patients were enrolled within 24 h of intubation. Primary outcome was the frequency of ICUAW on day 10 after ICU admission, defined by a Medical Research Council (MRC) sum score of <48. Secondary outcomes were the myosin-to-actin (M:A) ratio, strength progression and six month mortality. Results: A total of 46 out of 63 patients (73%) were diagnosed with ICUAW. Myosin loss correlated with muscle weakness and longer duration of mechanical ventilation. Overall, 29% had an M:A ratio ≤ 1.5 and 51% ≤ 1.7. In total, 58% of patients with an M:A ratio > 1.5 at day 10 reached the MRC sum score threshold at day 17 compared to 21% with an M:A ratio ≤ 1.5. Patients with ICUAW had a higher six-month mortality rate (24%) than patients without (0%). Conclusions: Absence of ICUAW at day 10 after ICU admission was related with a favourable outcome. Myosin loss with an M:A ratio ≤ 1.5 was associated with a slower recovery of muscle function.