Peripheral and segmental spinal abnormalities of median and ulnar somatosensory evoked potentials in Hirayama's disease

Quantitative assessment of motor impairment and surgical outcome in Hirayama disease with proximal involvement using motor unit number index

OBJECTIVE

To assess the feasibility of motor unit number index (MUNIX) in quantitatively evaluating Hirayama disease (HD) with proximal involvement and to identify the effectiveness of anterior cervical fusion (ACF) in treating atypical HD with proximal involvement.

METHODS

This study included 28 atypical HD patients with proximal involvement (proximal-distal vs. distal-proximal groups: 5 vs. 23) and 41 healthy controls. All patients underwent pre- and postoperative 1-year MUNIX tests on abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB) and deltoid (Del). The disabilities of arm, shoulder and hand (DASH) and Medical Research Council (MRC) scales were also performed in these patients before and one year after operation.

RESULTS

Preoperatively, the patients in the distal-proximal group showed reduced compound muscle action potential (CMAP), decreased MUNIX and increased motor unit size index (MUSIX) in bilateral distal muscles and symptomatic-side proximal muscles (P < 0.05), and similar abnormalities were also observed in ADM, BB and Del on the symptomatic side in the proximal-distal groups (P < 0.05). Postoperative follow-up analysis identified increased MUNIX in the symptomatic-side proximal muscles with improved motor function in the proximal-distal groups (P < 0.05), and distal-proximal group patients showed an increase in both CMAP and MUSIX in the symptomatic-side proximal muscles (P < 0.05).

CONCLUSIONS

MUNIX may serve as an available supplementary test to quantitatively evaluate the motor dysfunction and treatment outcome in HD with proximal involvement. ACF procedures can effectively treat these atypical HD patients, especially for those whose symptoms started in proximal muscles.

The reversible effect of neck flexion on the somatosensory evoked potentials in patients with Hirayama disease: a preliminary study

The aim of this study was to examine and characterize the reversibility of the cervical somatosensory electrophysiological pathways during neutral and flexed neck positions. The parameters of somatosensory evoked potentials (SEPs) during neutral and flexed neck positions (N9, N13, and N20 SEP latencies; N9-N13 and N13-N20 inter-peak latencies; and the changes in N9-N13 and N13-N20 inter-peak latency during neutral and flexed neck positions) were measured in the patients with Hirayama disease (HD) and also in the healthy controls. In patients with HD, there was a significant difference in the mean value of N13-N20 inter-peak latency during the flexed neck position compared to that of the healthy controls (p < 0.05). In a multivariate logistic regression analysis, N13-N20 inter-peak latency during the flexed neck position significantly correlated with the presence of HD (p < 0.05). Collectively, in this cohort of patients with HD, the neck flexion of patients with HD showed a reversible effect on the SEP parameter, especially in N13-N20 inter-peak latency. Conventional diagnosis of HD is based on nerve conduction studies and electromyography along with a cervical flexion MRI, and our study suggests the possibility of an additional and cost-effective electrophysiological marker that may be helpful in the diagnosis of HD.

Hirayama disease is a pure spinal motor neuron disorder--a combined DTI and transcranial magnetic stimulation study

Hirayama disease (HirD) is a juvenile spinal muscular atrophy predominantly affecting young men with an initially progressive course followed by a stable plateau within several years. It is a matter of debate whether HirD is a widespread motor neuron or more focal cervical cord disease. Whether the supraspinal pathways of the corticospinal tract (CST) are also affected has not been studied systematically. We analyzed CST integrity in seven HirD patients and 11 controls of similar age and gender using diffusion tensor imaging at a 1.5-T scanner and central motor conduction time (CMCT) using transcranial magnetic stimulation. The apparent diffusion coefficient, fractional anisotropy, and axial and radial diffusivity coefficients were determined bilaterally at four representative CST levels and along the whole CST using a probabilistic fiber tracking approach. There were no differences between the initially affected and the contralateral side in HirD patients and no difference between HirD patients and controls for both the ROI-based and the whole CST analyses. Radial diffusivity of the CST was positively correlated with years of disease progression in HirD patients. CMCT was normal in HirD patients. Combined anatomical and functional measurements established normal integrity of the supraspinal CST in HirD patients lending support to the notion that HirD is a pure spinal motor neuron disorder.

Monomelic neurogenic syndromes: a prospective study

Monomelic neurogenic syndromes are rare. Their classification and prognostic features have not been addressed in the European population. A prospective study of 17 patients with monomelic neurogenic amyotrophy, of upper or lower limb onset, with progression limited to one limb for three or more years. Clinical and neurophysiological studies were performed in the subsequent 3 or more years. Fifteen patients were of European origin and two were Asian. Those presenting with proximal monomelic weakness or with involvement of the posterior compartment of the lower leg showed no further progression after the initial period of development of the syndrome. Brisk reflexes in wasted muscles did not predict progression. Electromyographic signs of denervation in the opposite limb at presentation did not predict later progression. Transcranial magnetic stimulation (TMS) features of corticospinal dysfunction were a useful predictor of subsequent progression (p=0.01). One patient with lower limb onset developed conduction block with weakness in an upper limb nine years after presentation, and this upper limb weakness responded to IVIg therapy. This adult-onset European group of patients is different as compared with juvenile-onset Asian cases. The clinical syndromes appear heterogeneous, but neurophysiological investigations, in particular TMS, can be helpful in determining prognosis. Multifocal motor neuropathy should be considered when there is progression, even years after onset.