Changing perspectives: from neurophysiology to nerve ultrasound

ABSTRACT BACKGROUND Neuromuscular disorders impose significant challenges on individuals, their caregivers, and the healthcare systems. These conditions frequently stem from genetic factors, involve progressive degeneration, and affect life quality. In the Neuromuscular Unit the diagnostic work-up mainly relies on clinical and neurophysiological assessment. In the last years, high-resolution ultrasound examination of the Peripheral Nervous System has increasingly gained recognition as a complementary method finding numerous applications. This technique is able to provide useful information for the diagnosis and treatment of neuromuscular diseases. AIM This study series aims primarily to define the utility of nerve ultrasound in specific neuromuscular diseases, determining its feasibility and field of application. Secondly, it aims to investigate the association between clinical, neurophysiological and neurosonological findings. RESULTS Study 1 - Predicting value for incomplete recovery in Bell’s palsy of facial nerve ultrasound versus nerve conduction study. We prospectively enrolled 34 patients with Bell's palsy. All patients underwent neurophysiological testing and High-resolution Ultrasound (HRUS) of the facial nerve at 10-15 days (T1), one month (T2), and three months (T3) after the onset of Bell's palsy. We have then compared the accuracy of HRUS with that of the facial nerve conduction study in predicting incomplete clinical recovery at three and six months. We found that in the first days after Bell’s palsy onset, the diameter of the affected facial nerve is increased compared with the normal side, thus potentially enhancing the diagnostic assessment. The negative predictive value of a facial nerve diameter asymmetry of 25 % was relatively high (i.e., 94.73 %). Accordingly, we may speculate that an asymmetry lower than this threshold might be sensitive in detecting patients with a high probability of complete recovery. However, facial nerve HRUS examination has a poorer prognostic value than facial nerve conduction study in patients with Bell’s palsy. Study 2 - Nerve Ultrasound in Friedreich’s Ataxia: enlarged nerves as a biomarker of disease severity. Ten patients diagnosed with Friedreich’s Ataxia underwent an extensive clinical evaluation (SARA, FARS, mFARS, INCAT, ADL 0-36, IADL). Furthermore, they underwent nerve conduction study and nerve ultrasound. The assessment of nerve cross-sectional area, performed at 24 nerve sites, was compared to data collected from 20 healthy volunteers. All the patients had a severe sensory axonal neuropathy. HRUS showed a significant enlargement of median and ulnar nerves at the axilla and arm. The cumulative count of affected nerve sites was directly associated with clinical disability scales. Nerve ultrasound can offer valuable insights in cases where nerve conduction studies yield limited information. Nerve ultrasound is a potential biomarker of disease severity in Friedreich’s ataxia. Study 3 – Muscle ultrasound in Inclusion Body Myositis. We compared echo intensity (quantitative muscle ultrasound) and visual score (Heckmatt score) of a set of muscles (first dorsal interosseous, flexor digitorum profundus, biceps brachii, vastus lateralis, rectus femoris, tibialis anterior, medial and lateral gastrocnemius) in patients with IBM (n=10) and healthy controls (n=20). Echo intensity was higher in most of the examined muscles (flexor digitorum profundus, biceps brachii, vastus lateralis, rectus femoris, tibialis anterior and medial gastrocnemius) in IBM compared to controls. Muscle ultrasound findings correlate with clinical measures (the higher the muscle echo intensity/Heckmatt score, the lower the MRC score of the explored muscle), thus supporting the use of muscle ultrasound in this rare condition. Muscle ultrasound is an easy to perform, inexpensive and reliable diagnostic tool in IBM. CONCLUSIONS Neuromuscular ultrasound is an noninvasive tool that provides useful information complementary to neurophysiological data, offering support in investigating peripheral nervous system diseases. It can provide prognostic information (Study 1), and give valuable insights correlating with clinically assessed disability (Study 2 and Study 3). The implementation of standardized scanning protocols is of paramount importance in order to improve patient care and support a greater applicability of this technique among neurophysiologists.