P-NU004. Nerve ultrasound in multifocal motor neuropathy: Correlation with electrophysiology and functional disability

Abstract

Introduction . Increased nerve cross-sectional area (CSA) on ultrasound is associated with conduction block in multifocal motor neuropathy (MMN). We investigated the ultrasound features of peripheral nerves in MMN and their correlation with electrophysiology and functional disability. Methods . MMN patients fulfilling the EFNS/PNS criteria were recruited from University Malaya Medical Centre, Kuala Lumpur, Malaysia. All patients underwent neurological assessment with MRC sumscore, grip strength, INCAT disability score, and had nerve conduction studies. Each patient also underwent nerve ultrasound study using a standardized protocol. Age- and gender-matched healthy controls were recruited for comparison. Results . Three MMN patients (2 men) aged 46.3±10.6 years and three normal controls were included. Mean disease duration was 4.3±2.5 years (ranged 1.5-6.0). CSF protein ranged 0.25-0.50 g/L with a mean 0.40±0.13 g/L. One patient was positive for anti-GM1 IgM. Mean MRC was 55.0±5.3 (range 49-59), handgrip (right: 13.2±8.1 kg; left: 21.7±11.9 kg) and INCAT 3.7±1.1 (range 3-5). Nerve CSAs were significantly larger in MMN patients than normal controls in median (forearm: p=0.043), ulnar (forearm: p=0.047), tibial (knee: p=0.002), radial (p=0.002) and sural (p<0.001) nerves. The side-to-side difference ratio of intranerve CSA variability (ICSAV) for ulnar nerve (p=0.046) was significantly larger in MMN patients. The nerve CSAs were significantly correlated with MRC [median midarm/forearm ratio (p=0.004); ulnar ICSAV (p=0.037)] and INCAT [median: elbow (p=0.029), midarm (p=0.030) and midarm/forearm ratio (p=0.007); ulnar ICSAV (p=0.029)]. Correlation analysis with electrophysiology found increased nerve CSAs significantly correlated with distal motor latency [median: wrist (p=0.042), ICSAV (p=0.005)]; and inversely correlated with motor conduction velocity [median ICSAV (p=0.042)] and proximal/distal CMAP ratio [tibial knee (p=0.005)]. Conclusion . In MMN, nerve enlargement was focal, at non-entrapment sites, asymmetrical and can involve the sensory nerve. Nerve ultrasound significantly correlates with functional disability and electrophysiological parameters suggesting that it may be useful as an additional diagnostic biomarker in MMN.