Sonographic Evaluation of Muscle Echogenicity for the Detection of Intensive Care Unit-Acquired Weakness: A Pilot Single-Center Prospective Cohort Study

Abstract

Qualitative assessment by the Heckmatt scale (HS) and quantitative greyscale analysis of muscle echogenicity were compared for their value in detecting intensive care unit-acquired weakness (ICU-AW). We performed muscle ultrasound (MUS) of eight skeletal muscles on day 3 and day 10 after ICU admission. We calculated the global mean greyscale score (MGS), the global mean z-score (MZS) and the global mean Heckmatt score (MHS). Longitudinal outcome was defined by the modified Rankin scale (mRS) and Barthel index (BI) after 100 days. In total, 652 ultrasound pictures from 38 critically ill patients (18 with and 20 without ICU-AW) and 10 controls were analyzed. Patients with ICU-AW had a higher MHS on day 10 compared to patients without ICU-AW (2.6 (0.4) vs. 2.2 (0.4), p = 0.006). The MHS was superior to ROC analysis (cut-off: 2.2, AUC: 0.79, p = 0.003, sensitivity 86%, specificity 60%) in detecting ICU-AW compared to MGS and MZS on day 10. The MHS correlated with the Medical Research Council sum score (MRC-SS) (r = -0.45, p = 0.004), the mRS (r = 0.45; p = 0.007) and BI (r = -0.38, p = 0.04) on day 100. Qualitative MUS analysis seems superior to quantitative greyscale analysis of muscle echogenicity for the detection of ICU-AW.

Keywords: ICU-AW; diagnostic ultrasound; muscle echogenicity; muscle weakness.

Figure 1

Flowchart of patient screening and study cohort inclusion. Feasibility of MRC-SS testing was checked by using standardized requests the patient had to follow: “Open and close your eyes”, “Look at me”, “Open your mouth and put out your tongue“, “Nod your head”, “Raise your eyebrows until I have counted to five”. ICU-AW was assumed with an MRC-SS < 48. ICU-AW+: patients with intensive care unit-acquired weakness. ICU-AW−: patients without intensive care unit-acquired weakness. ICU: intensive care unit. MRC-SS: Medical Research Council sum score. SOFA: Sequential Organ Failure Assessment score.

Figure 2

Longitudinal assessment of the MGS in ICU-AW+ patients, ICU-AW− patients and healthy controls on days 3 and 10. ICU-AW: intensive care unit-acquired weakness. ICU-AW+: patients with intensive care unit-acquired weakness. ICU-AW−: patients without intensive care unit-acquired weakness. ICU: intensive care unit. MGS: global mean greyscale score.

Figure 3

Longitudinal assessment of the MHS in ICU-AW+ patients, ICU-AW− patients and healthy controls on days 3 and 10. ICU-AW: intensive care unit-acquired weakness. ICU-AW+: patients with intensive care unit-acquired weakness. ICU-AW−: patients without intensive care unit-acquired weakness. ICU: intensive care unit. MHS: global mean Heckmatt score.

Figure 4

ROC curves of ultrasonographic parameters on study days 3 and 10. MGS: global mean greyscale score. MHS: global mean Heckmatt score. MZS: global mean z-score. ROC: receiver operating characteristics.

Figure 5

Correlation of the MHS with clinical outcome parameters. Correlation of the MHS on day 10 with the MRC-SS on day 10 (a), the BI (b) and the mRS on day 100 (c). BI: Barthel index. MHS: global mean Heckmatt score. MRC-SS: Medical Research Council sum score. mRS: Modified Rankin scale. r: correlation coefficient.

Figure 6

Differences in assessment of muscle echogenicity. (a1) Qualitative assessment of muscle echogenicity of the tibialis anterior muscle of an ICU-AW− patient with increased muscle echo intensity, but nearly fully visible cortical bone echo signal (white arrows), rated with the Heckmatt scale (HS). (a2) Quantitative assessment of muscle echogenicity of the same muscle depicted in a1 using ImageJ by selecting a region of interest (yellow marked; the acoustic shadow image artifact behind the central tibialis anterior aponeurosis has been excluded) within the affected muscle and consecutive greyscale analysis (GS) with the corresponding histogram (a3). (b1) Qualitative assessment of muscle echogenicity of the tibialis anterior muscle of an ICU-AW+ patient with increased muscle echo intensity and nearly vanished cortical bone echo signal, rated HS 3. (b2) Quantitative assessment of muscle echogenicity of the same muscle depicted in b1 using ImageJ by selecting a region of interest (yellow marked) within the affected muscle and consecutive GS with the corresponding histogram in (b3). The mean GS values of the quantitative assessments (a3,b3) are almost equal, so patients with ICU-AW cannot be distinguished from patients without ICU-AW. In contrast, in the qualitative assessments (a1,b1) using the HS, a clear difference in the visibility of the tibialis cortical bone echo signal between ICU-AW+ and ICU-AW- patients can be seen.