Background/Purpose: The Heckmatt grading scale has been widely used as a semiquantitative assessment method for grading muscle echo intensity (EI) on ultrasound; however, this was originally developed for muscular dystrophies in the 1980s. Concerns have been raised regarding poor agreement among assessors and inadequate capture of changes seen with acute myositis. In this study, we test the reliability and construct validity of a new 4-point, semiquantitative grading scale developed for myositis, which defines increases in muscle EI relative to surrounding structures and incorporates changes in muscle architecture that occur with inflammation and damage.

Methods: Ultrasound images of deltoid, biceps brachii, and rectus femoris muscles of myositis patients and controls, obtained from 2015 to 2018 were included in this study. Two experienced raters and one less experienced rater, who had received a two-hour lecture and one training session before the assessment, independently assessed the images. We defined the Hopkins myositis grading scale as follows;Grade 1: Normal – muscle EI equal to or lower than the overlying fat, with clear contrast to perimysial septation and fasciaGrade 2: Mildly Abnormal – muscle EI is slightly increased, may be higher than that of overlying fat layer but lower than that of fascia, but perimysial septations remain well-definedGrade 3: Moderately Abnormal – muscle EI is high but is still less echogenic than fascia, with loss or blurring of contrast to perimysial septationGrade 4: Severely Abnormal – muscle EI is very high, equal to or nearly equal to fascia, potentially accompanied by acoustic shadowsConstruct validity was evaluated using Spearman’s correlation between each grading system and muscle strength, as well as quantitative muscle EI. Interrater and intrarater reliability were evaluated using Cohen’s kappa. Cohen’s kappa was interpreted as substantial for 0.60-0.80 and almost perfect for 0.80-1.00.

Results: A total of 349 images from 61 myositis patients (26 inclusion body myositis (IBM) and 35 non-IBM myositis), and 222 images from 37 healthy controls were included. The Hopkins myositis grading scale demonstrated good correlations with both muscle strength and EI, ranging between rho 0.55 – 0.62, better than the Heckmatt scale (Table). In myositis patients, interrater reliability of the Hopkins myositis grading scale demonstrated substantial agreement (Cohen’s kappa 0.62 – 0.65) while the Heckmatt scale had fair agreement (Cohen’s kappa 0.28 – 0.36). Similarly, intrarater reliability of the Hopkins myositis grading scale was almost perfect and better than the Heckmatt scale (0.78-0.85 vs 0.67).

Conclusion: In myositis patients, the Hopkins myositis grading scale which incorporates more specific parameters to aid in assessing changes in muscle EI and architecture, showed excellent validity and reliability and showed improvements over the original Heckmatt scale. Notably, the less experienced rater demonstrated interrater reliabilities comparable to those of the experienced raters, suggesting that appropriate training can be sufficient for accurate assessment.

Figure 1. The Hopkins myositis grading scale in healthy controls (A-C) and myositis patients (D-F: immune mediated necrotizing myopathy, G-I: Anti-synthetase syndrome, J-L: inclusion body myositis). A, D, G, J: deltoid. B, E, H, K: biceps brachii. C, F, I, L: rectus femoris. Abbreviation: Hp: the Hopkins myositis grading scale, He: the Heckmatt grading scale.

Table 1. Validity and reliability of the Hopkins myositis grading scale and the Heckmatt grading scale.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validity-and-reliability-of-a-new-ultrasound-based-semiquantitative-echogenicity-grading-scale-for-myositis/