Optimizing hand-function patient outcome measures for inclusion body myositis

Abstract

Inclusion body myositis is the most commonly acquired myopathy after the age of 45. The slowly progressive and heterogeneous disorder is a challenge for measuring clinical trial efficacy. One current method for measuring progression utilizes the Inclusion Body Myositis-Functional Rating Scale. We have found that the upper extremity domain scores in the Inclusion Body Myositis-Functional Rating Scale do not consistently change until there is extreme loss of grip and finger flexor strength. Therefore, we performed a cross-sectional observational study of 83 inclusion body myositis patients and 38 controls recruited at the 2019 Annual Patient Conference of The Myositis Association. We evaluated new Inclusion Body Myositis Patient-Reported Outcome measures for upper extremity function modified from the NIH Patient-Reported Outcomes Measurement Information System as well as pinch and grip strength. We found that Patient-Reported Outcome measures hand-function have a higher correlation with pinch and grip strength than the Inclusion Body Myositis-Functional Rating Scale.

Keywords: Functional rating scale; Grip strength; Inclusion body myositis; Outcome measures; Patient reported outcome; Pinch strength.

Fig. 1.

(A) Grip strength (non-normalized) averaged over three trials of control patients (blue circles) and patients with IBM (red squares). (B) Histogram of frequency by decile bins of grip strength normalized to age and sex of control patients (blue) and patients with IBM (red). (C) Mean pinch strength by CITEC dynamometer with the pinch grip applicator differentiated by age. As there is no normalized data, (D) presents histogram of frequency by one pound of pinch strength.

Fig. 2.

(A) Comparison of pinch strength (by CITEC dynamometer) versus finger flexor strength measured semi-quantitatively (r = 0.79) and grip strength measured by dynamometer (r = 0.77). Patients with IBM in squares and controls in circles. (B) Comparison of pinch versus hand grip strength among patients with IBM (square) and control (circle). Dotted lines denote median pinch and median hand grip strength of IBM cohort. Solid lines and shaded gray areas correspond to localized smoothed means and 95% confidence intervals of smoothed means, respectively. (C) Normalized grip strength can be calculated given published baseline for age and sex, but this is not available for pinch. Normalization more clearly shows that pinch and grip are independent measures.

Fig. 3.

Box plot of grip strength and patient’s rating of individual 12-item IBM-PRO Upper Extremity Function Scale.

Fig. 4.

Box plot of pinch strength and patient’s rating of individual 12- item IBM-PRO Upper Extremity Function Scale.

Fig. 5.

IBM-FRS hand item sum (A) and IBM Upper Extremity Function Scale sum (D) plotted against patient-reported disease duration. No clear decline with time is seen, which is consistent with the heterogeneity of the patients in a cross-sectional study. However, the IBM-PRO Upper Extremity Function Scale have a higher correlation with grip (E) and pinch (F) strength than FRS hand item sum (B and C, respectively).