Transcranial Magnetic Stimulation-Induced Motor Evoked Potentials in Hirayama Disease: Systematic Review of the Literature.

Abstract

Hirayama disease (HD) is a rare motor disorder mainly affecting young men, characterized by atrophy and unilateral weakness of forearm and hand muscles corresponding to a C7-T1 myotome distribution. The progression is self-limited. The etiology of HD is unclear. The usefulness of motor evoked potentials (MEPs) in pyramidal tracts damage evaluation still appears to be somehow equivocal. We searched PubMed for original articles, evaluating the use of transcranial magnetic stimulation elicited MEPs in HD using keywords "motor evoked potentials Hirayama" and "transcranial magnetic stimulation Hirayama." We found seven articles using the above keywords that met inclusion criteria. The number of participants was small, and diagnostic procedures varied. There were also differences in methodology. Abnormal central motor conduction time was found in 17.1% of patients in one study, whereas it was normal in two other studies. Peripheral motor latency was evaluated in one study, which found abnormally increased peripheral motor latencies in at least one tested muscle in 16 of 41 HD patients (39.0%). Abnormal MEP parameters were found in three studies in 14.3% to 100% patients. In one study they were not evaluated, in three other studies they were normal, and in one they were normal also in standard and flexed neck position In one study, inconsistent results were found in MEP size after neck flexion in patients after treatment with neck collar. Although MEP parameters may be abnormal in some HD patients, these have not been thoroughly assessed. Further studies are indispensable to evaluate their usefulness in assessing pyramidal tract damage in HD.