Determine the feasibility and utility of handheld neuromuscular ultrasound in the assessment of patients with sporadic inclusion body myositis (sIBM).

sIBM can be difficult to diagnose from other causes of painless weakness.  One of the hallmarks of the disease is weakness of the deep finger flexors that may be missed by those who do not routinely see sIBM.  In particular, comparison of echogenicity between the flexor digitorum profundus (FDP) and flexor carpi ulnaris (FCU) muscles with relative FCU sparing has been shown to provide diagnostic specificity for sIBM from other neuromuscular diseases.

15 patients with sIBM (mean age: 69.9 ± 7.2 years; 60% male; 11.2 ± 7.0 years since symptom onset; 80% with confirmed histopathological diagnosis) underwent ultrasound assessment with the handheld Butterfly iQ+ ultrasound. Pinch, and grip strength were measured quantitatively with dynamometry. Disability and physical function were measured using patient-reported outcomes.  The semi-quantitative Heckmatt grading scale was used to measure muscle echogenicity.

Heckmatt echogenicity for the FDP and FCU was found to moderately correlate with ipsilateral hand grip strength (FCU: rho = -0.68, p = 0.007; FDP: rho = -0.56, p = 0.036) as well as pinch strength. Increasing echogenicity of the FDP and FCU combined in the dominant forearm was also moderately correlated with decreasing hand function as reported by the patient-reported IBM Upper Extremity Function scale (rho = -0.64, p = 0.019). 67% of patients had increased FDP echogenicity compared to FCU.

Increased muscle echogenicity on the Heckmatt scale, reflecting fibrosis and fatty infiltration, is associated with decreasing muscular strength and patient reported outcomes in patients with sIBM. The Butterfly iQ+ is a low-cost, safe, and non-invasive tool for assessing muscle involvement in sIBM.