Effect of neck flexion on F wave, somatosensory evoked potentials, and magnetic resonance imaging in Hirayama disease

Abstract

Background: Flexion myelopathy is one of the suggested mechanism for Hirayama disease (HD) but simultaneous radiological and neurophysiological evaluation is lacking. This study therefore evaluates the effect of neck flexion in HD using somatosensory evoked potentials (SEPs), F waves, and magnetic resonance imaging (MRI). Method: Eight HD patients and seven matched controls were subjected to median and ulnar F wave (minimal latency, FM ratio, persistence, and chronodispersion), and SEPs evaluating N9, N13, and N20 potentials in neutral and neck flexion. Spinal MRI was carried out in neutral and neck flexion and evaluated for cord atrophy, signal changes, cord compression, posterior epidural tissue, and loss of dural attachment. Results: The patients were aged 19 to 30 years. Minimal F latency, FM ratio, persistence, and chronodispersion in neutral and neck flexion did not show any change nor was there any change in N13 latency and amplitude on median and ulnar SEPs. The difference in these parameters in neutral and neck flexion were also not significant in HD compared with controls. The change in N13 was also not related to loss of dural attachment and posterior epidural tissue. Conclusion: Neck flexion does not produce significant changes in N13 and F wave parameters and is not related to dynamic MRI changes. The other mechanisms for HD should therefore be explored.

Monomelic neurogenic syndromes: A prospective study

“…Although we noted this phenomenon in some of our patients it did not predict disease progression. In our population SEP's studies were normal, as has been reported in Asian patients, [12,51] although mild changes were described in one study [52]. EMG abnormalities beyond the territory of clinically affected muscles are often suggested as predictive of progression to clinical involvement of other limbs.…”

Nosology of Juvenile Muscular Atrophy of Distal Upper Extremity: From Monomelic Amyotrophy to Hirayama Disease—Indian Perspective

“…Because of chronic denervation there may be prolongation of latency, decline in persistence, and reduction in amplitude; however depending on reinnervation, the amplitudes may increase. In patients with severe wasting, the F wave may become unrecordable [36]. …”

A severe case of Hirayama disease successfully treated by anterior cervical fusion

“…EMG typically shows the presence of neurogenic lesions in all affected muscles with spontaneous potentials, a prolonged duration or augmentation of amplitude in motor unit potentials, or an incomplete pattern of recruitment. 5,[18][19][20]28 Electrophysiological studies performed during neck flexion failed to prove abnormalities related to neck posture, 20 although those studies were performed at the plateau phase of the disease, and there was no mention of how long flexion was maintained.…”