What are the key pathophysiologic processes characteristic of critical-illness myopathy (CIM)?

• A. Myosin loss and bioenergetic failure
• B. Increased mitochondrial biogenesis
• C. Muscle hypertrophy with increased strength
• D. Nerve conduction block without muscle pathology

Answer: (A)

Critical-illness myopathy involves direct muscle fiber pathology driven by loss of contractile proteins and impaired energy production. The best description is selective loss of myosin heavy chains along with other sarcomeric proteins, accompanied by bioenergetic failure from mitochondrial dysfunction. This combination reduces the muscle’s ability to generate force, leading to weakness even with preserved nerve input. It also reflects increased proteolysis and disrupted energy pathways that collectively diminish ATP availability for contraction.

In contrast, increased mitochondrial biogenesis would tend to enhance energy capacity rather than diminish it, which doesn’t fit CIM. Muscle hypertrophy with stronger strength is the opposite of the weakness seen in CIM. Nerve conduction block without muscle pathology points to a neuropathic process, not a primary muscle disease.