Objective: To assess muscle strength in patients with idiopathic inflammatory myopathies (IIM) using neuromuscular scales and isokinetic testing.
Methods: Muscle function was evaluated in 27 IIM patients being followed at the Rheumatology Unit of the University of Pisa using: (i) a modified version of the grading system used to assess Duchenne dystrophy, (ii) the four-stage grading system of Henriksson and Sandstedt, (iii) an isokinetic muscle strength test (Kin Com, Chatanooga) and (iv) the Health Assessment Questionnaire (HAQ).
Results: The neuromuscular scales showed normal or only mildly impaired muscle strength in 60% (Duchenne scale) and 80% (Henriksson and Sandstedt scale) of the patients, respectively, whereas isokinetic testing detected moderate to severe reductions in muscle strength in almost 70% of the patients. No correlations were observed between muscle strength and disease activity, therapy, age at evaluation and disease duration. There was a correlation between the results of the HAQ and neuromuscular testing, but not the isokinetic test.
Conclusions: Although less easy and more expensive to administer, isokinetic testing appears to be a more sensitive instrument than the standard neuromuscular tests for assessing muscle function in IIM patients. In particular, it can detect small reductions in muscle strength.