Diagnosis of critical illness myopathy by muscle biopsy can be difficult, especially early in the disease course. Stibler et al used the ratio of myosin to actin to identify patients with this disorder. The authors are from the Karolinska Institute in Stockholm, Sweden.



(1) Muscle biopsy tissue is homogenized and processed to prepare a supernatant containing actin and myosin.

(2) Actin and myosin are separated using SDS polyacrylamide gel electrophoresis (PAGE).

(3) The bands are scanned using a linear densitometer.

(4) The background optical density is used to establish the base of each peak and then the peak area in square mm is determined.


ratio of myosin to actin =

= (area under myosin peak in square mm) / (area under the actin peak in square mm)



• Patients without myopathy had a ratio > 1.0, with most > 1.2.

• Patients with myopathy had a ratio < 0.4.

• Patients in recovery had an increase in the ratio to 0.6 to 0.8 range.

• Patients with axonal neuropathy had a ratio in the normal range (> 1.0).


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