Electrophoretic determination of the myosin/actin ratio in the diagnosis of critical illness myopathy

Objective. To develop a rapid method to quantify myosin in muscle biopsy specimens from patients with critical illness myopathy (CIM). Design. Percutaneous muscle biopsy specimens at different stages of CIM were examined by light microscopy and transmission electron microscopy (TEM) and by horizontal pore gradient SDS electrophoresis (SDS-PAGE). The myosin/actin ratio was calculated densitometrically. Neurophysiological examinations were performed at various times during the course of CIM. Setting. All patients were treated in intensive care units at Karolinska Hospital. Patients and participants. We studied 11 patients with CIM, 5 patients with axonal neuropathies, and 42 control individuals. Measurements and results. The histopathological changes included in all cases muscle fiber atrophy, degeneration, regeneration, nuclear changes, and reduction in myofibrillar ATPase activity in both type I and II fibers. In severely affected muscles fiber type differentiation was lost. On TEM preferential loss of thick filaments was the dominant finding. In some patients changes were present only in parts of the specimen. The neurophysiological examinations indicated myopathy in five patients and combined myopathy and neuropathy in five and suggested neuropathy in one. The SDS-pore PAGE used showed a technical variation of 4-5%. Quantitative results were obtained within 1 day and night. The mean value of the myosin/actin ratio in controls was 1.37+/-0.21 and in CIM patients 0.37+/-0.17, without overlapping with the control values. Conclusions. Considering the diagnostic difficulty using morphological and neurophysiological methods, especially in early stages of CIM, we suggest including SDS-pore PAGE to determine the myosin/actin ratio for rapid diagnosis of CIM.