P.18.3 Test–retest reliability of strength measurements of the long finger flexors (LFF) in patients with myotonic dystrophy type 1

Abstract

Patients with myotonic dystrophy (DM1) have distal upper extremity weakness which initially focuses on the long finger flexors. Grip strength using a Jamar dynamometer with the handle in the second position has provided reliable measurement of hand strength in patients with DM1. Grip strength however, is a measure of intrinsic and extrinsic hand muscle strength and does not isolate the LFF. The use of the Jamar dynamometer with the handle in the furthest position, contacting the distal phalanx, isolates the flexor digitorum profundus. Pinch also relies on long finger flexor strength. There are no established testing procedures in DM1 to specifically examine the LFF. To pursue this goal, this study investigates test–retest reliability of strength measurements of the LFF in patients with DM1. We measured strength of the LFF by manual muscle testing (MMT) and quantitative muscle testing (QMT) in 26 patients with DM1. MMT was performed bilaterally on the LLF of the thumb, first and second digits using standard MRC procedures and grading. QMT was performed using a Jamar hand dynamometer on the furthest setting and the palmar pinch was measured using a pinch gauge (B & L Engineering). These testing procedures were performed twice in a 24 h period (ranging from 18–24 h apart). The weighted kappa statistic for LFF’s using MMT were 0.84 (right) and 0.92 (left). The ICC for the LFF using the Jamar dynamometer was 0.95 (right) and 0.92 (left). The ICC for palmar pinch was 0.95 (right) and 0.96 (left). Strength testing of the LFF demonstrated excellent intra-rater reliability over a 24 h period. Tests of sensitivity to change over longer periods of time are necessary to establish the usefulness of these tests as outcome measures for clinical trials.