title: A study of dynamic F-waves in juvenile spinal muscular atrophy of the distal upper extremity (Hirayama disease).
abstract: OBJECTIVE
  The study aimed to analyse changes in the upper limb F-waves during neck flexion in patients with Hirayama disease (HD).
  
  
  METHODS
  This study included 41 healthy subjects, 38 HD patients and 24 patients with amyotrophic lateral sclerosis (ALS). Bilateral F-waves were consecutively recorded 20 times with the neck both in the standard position and after persistent neck flexion for 30min. The persistence, minimal latencies, chronodispersion, F/M ratios and amplitudes of the F-waves and repeater F-waves were compared between the standard neck and neck flexion positions.
  
  
  RESULTS
  During neck flexion, repeater F-waves were found in more HD patients, the percentage of both the ulnar and median repeater F-waves increased significantly, and higher F/M ratios were observed on the symptomatic side (P<0.05). No differences in the F-waves were observed in the healthy subjects or the ALS patients during neck flexion (P>0.05).
  
  
  CONCLUSIONS
  HD might be more likely to present as a position-related dysfunction rather than a spinal cord-intrinsic disease. Thus, HD patients could be counselled to avoid neck flexion for long periods of time to prevent further damage, especially in the progressive stage of the disease.
authors.affiliation: Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai 200040, China.
authors.forename: Chaojun
authors.initials: C
authors.lastname: Zheng
authors.affiliation: Department of Physical Medicine and Rehabilitation, Upstate Medical University, State University of New York at Syracuse, Syracuse, NY 10212, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai 200040, China.
authors.forename: Shuo
authors.initials: S
authors.lastname: Yang
authors.affiliation: Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai 200040, China; Department of Orthopedics, The Fifth People's Hospital, Fudan University, Shanghai 200240, China.
authors.forename: Feizhou
authors.initials: F
authors.lastname: Lu
authors.affiliation: Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai 200040, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Jin
authors.affiliation: Department of Physical Medicine and Rehabilitation, Upstate Medical University, State University of New York at Syracuse, Syracuse, NY 10212, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Weber
authors.affiliation: Department of Orthopedics, Huashan Hospital, Fudan University, Shanghai 200040, China. Electronic address: jianyuanjiang05@126.com.
authors.forename: Jianyuan
authors.initials: J
authors.lastname: Jiang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004568:Electrodiagnosis; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging / Q000503:physiopathology*; D009334:Neck Muscles / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014897:Spinal Muscular Atrophies of Childhood / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D014459:Ulnar Nerve / Q000503:physiopathology; D014953:Wrist / Q000473:pathology / Q000503:physiopathology; D055815:Young Adult
keywords: Amyotrophic lateral sclerosis; F-wave; Hirayama disease; Neck flexion