Handheld dynamometry effective for muscle strength assessment in polymyositis
DESTIN, Fla. — Handheld dynamometry, a new, inexpensive and quantitative compact device, proved reliable and effective in evaluating muscle strength in a large cohort of patients with idiopathic inflammatory myopathies, and could serve as an objective alternative to manual muscle testing, according to a presenter at the 2019 North American Young Rheumatology Investigator Forum.
“Manual muscle testing is the method of choice for assessing muscle strength in more than 90% of clinical trials so far in myositis — it’s easily administered, it takes about 5 to 10 minutes to complete and everyone knows about it, and you don’t need any equipment,” Didem Saygin, MD, a resident in training at the University of Pittsburgh, told attendees. “However, there have been several studies showing bias with examiner strength, with gender and experience, as well as with the patient’s weight, motivation and the degree of muscle atrophy — it all affects the grading of muscle strength in manual muscle testing.”
“We strongly believe that we need more objective outcome measures, and specifically for muscle strength,” she added. “So, in search of an objective measure, we came across handheld dynamometry, a portable, small, battery-operated device, which had demonstrated reliability in previous studies among patients with neuromuscular diseases.”
To test the reliability, validity and responsiveness of handheld dynamometry as an objective outcome measure in patients with idiopathic inflammatory myopathies, Saygin and colleagues conducted a longitudinal, prospective study of 50 patients, including 11 with polymyositis, 28 with dermatomyositis, seven with necrotizing myopathy and four with anti-synthetase syndrome.
Participants were evaluated using the six validated core set measures for myositis — manual muscle testing, physician global disease activity, patient global disease activity, extra-muscular global disease activity, health assessment questionnaire and muscle enzymes — as well as three functional measures — 6-minute walk, timed up-and-go and sit-to-stand tests — at baseline and at 3 and 6 months. During each visit, the researchers also used handheld dynamometry to test participants’ strength on three consecutive attempts.
Saygin and colleagues evaluated test-retest reliability by calculating correlations between three measurements completed by a single examiner, who used Spearman correlation. The researchers compared handheld dynamometry manual muscle testing, as well as the other core set measures and functional tests. Outcome variables included physician-reported change, total improvement score and ACR/EULAR response groups to determine the device’s responsiveness.
According to Saygin, handheld dynamometry demonstrated strong test-retest reliability (Rho = 0.96) and excellent internal consistency (Cronbach- = 0.95) and correlated moderately with manual muscle testing scores (R = 0.44; P = .003). In addition, the device showed moderate to strong correlation with physician global disease activity (R = -0.4; P = .006) and the health assessment questionnaire (R = -0.5; P = .0005), as well as the sit-to-stand (R = 0.5; P = .0002) and 6-minute-walk (R = 0.4; P = .005) tests.
Saygin also stated that longitudinal change in handheld dynamometry strongly correlated with total improvement score at 6 months (R = -0.6; P = .01). In addition, scores on the device changed significantly among patients in physician-reported “moderately-better” and “a-little-better” groups (P = .01). According to Saygin, this demonstrated responsiveness to change. Meanwhile, the device’s results did not change longitudinally among patients with stable disease, demonstrating reliability, she said. Both manual testing and the device demonstrated similar correlations with the conventional core set measures.
However, the effect size and the standardized response mean of handheld dynamometry was higher than that of manual testing.
“Handheld dynamometry demonstrates strong internal consistency and reliability, construct validity and responsiveness in a large myositis cohort,” Saygin said. “Handheld dynamometry may serve as an objective alternative to manual muscle testing to quantify muscle strength, which can in turn optimize the evaluation of treatment response in clinical trials and routine practice.” – by Jason Laday
Saygin D. A new tool to assess muscle strength in polymyositis and dermatomyositis: Handheld dynamometry. Presented at: North American Young Rheumatology Investigator Forum; May 1, 2019; Destin, Fla.
Disclosure: Saygin reports no relevant financial disclosures.