Fasciculation distribution in a healthy population assessed with diffusion tensor imaging

Fasciculations, a hallmark of motor neuron diseases, also occur in healthy individuals, highlighting the need to understand fasciculation intensity and distribution. Motor unit MRI (MUMRI) can assess fasciculations in large volumes but is not widely applied. We hypothesize that a more common MRI technique, diffusion tensor imaging (DTI), can also detect fasciculation when correcting for low signal-to-noise ratios and signal variability. We first systematically compared MUMRI and DTI in upper leg muscles of healthy subjects (n = 5). Secondly, we retrospectively determined fasciculation intensity and distribution in lower extremity muscles of 30 healthy subjects using DTI (n = 30). DTI and MUMRI had comparable sensitivity (75%) and precision (80%) to expert reviews. In our healthy cohort, fasciculations were more prevalent in the lower legs than upper legs (13.9 ± 11.5% vs. 9.8 ± 6.3%, p = 0.011), particularly in the soleus (9.3 ± 8.1%). This effect persisted after normalizing for muscle volume (7.2 ± 5.1%/dm³ vs. 2.9 ± 1.8%/dm³, p < 0.001). Lower leg fasciculations were larger compared to upper leg fasciculations (0.81 ± 0.31 cm³ vs. 0.54 ± 0.15 cm³, p < 0.001). Longitudinal analysis showed consistent fasciculation distribution over 8 months (n = 13, ICC = 0.803). In conclusion, muscle DTI detects fasciculations in all lower extremity muscles, enabling retrospective analysis of existing datasets and reducing the need for prospective MUMRI studies if muscle DTI is already acquired.