title: Whole-Body Muscle MRI in Patients with Hyperkalemic Periodic Paralysis Carrying the SCN4A Mutation T704M: Evidence for Chronic Progressive Myopathy with Selective Muscle Involvement.
abstract: OBJECTIVE
  Hyperkalemic periodic paralysis (hyperKPP) is a muscle sodium-ion channelopathy characterized by recurrent paralytic attacks. A proportion of affected individuals develop fixed or chronic progressive weakness that results in significant disability. However, little is known about the pathology of hyperKPP-induced fixed weakness, including the pattern of muscle involvement. The aim of this study was to characterize the patterns of muscle involvement in hyperKPP by whole-body magnetic resonance imaging (MRI).
  
  
  METHODS
  We performed whole-body muscle MRI in seven hyperKPP patients carrying the T704M mutation in the SCN4A skeletal sodium-channel gene. Muscle fat infiltration, suggestive of chronic progressive myopathy, was analyzed qualitatively using a grading system and was quantified by the two-point Dixon technique.
  
  
  RESULTS
  Whole-body muscle MRI analysis revealed muscle atrophy and fatty infiltration in hyperKPP patients, especially in older individuals. Muscle involvement followed a selective pattern, primarily affecting the posterior compartment of the lower leg and anterior thigh muscles. The muscle fat fraction increased with patient age in the anterior thigh (r=0.669, p=0.009), in the deep posterior compartment of the lower leg (r=0.617, p=0.019), and in the superficial posterior compartment of the lower leg (r=0.777, p=0.001).
  
  
  CONCLUSIONS
  Our whole-body muscle MRI findings provide evidence for chronic progressive myopathy in hyperKPP patients. The reported data suggest that a selective pattern of muscle involvement-affecting the posterior compartment of the lower leg and the anterior thigh-is characteristic of chronic progressive myopathy in hyperKPP.
authors.affiliation: Department of Radiology, Research Institute of Radiological Science, Medical Convergence Research Institute, Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Young Han
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Department of Neurology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Hyung Soo
authors.initials: HS
authors.lastname: Lee
authors.affiliation: Department of Neurology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Hyo Eun
authors.initials: HE
authors.lastname: Lee
authors.affiliation: Department of Radiology, Research Institute of Radiological Science, Medical Convergence Research Institute, Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Seok
authors.initials: S
authors.lastname: Hahn
authors.affiliation: Department of Neurology, Chonnam National University Medical School, Gwangju, Korea.
authors.forename: Tai Seung
authors.initials: TS
authors.lastname: Nam
authors.affiliation: Department of Neurology, Yonsei University College of Medicine, Seoul, Korea. hayshin@yuhs.ac.
authors.forename: Ha Young
authors.initials: HY
authors.lastname: Shin
authors.affiliation: Department of Neurology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Young Chul
authors.initials: YC
authors.lastname: Choi
authors.affiliation: Department of Neurology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Seung Min
authors.initials: SM
authors.lastname: Kim
keywords: chronic progressive myopathy; fat quantification; hyperkalemic periodic paralysis; muscle MRI; two-point Dixon technique