Cylindrical spirals in a familial neuromuscular disorder

Area of Science:

• Muscle Biology
• Cellular Ultrastructure
• Neuromuscular Disorders

Background:

• Cylindrical spirals, unique membranous structures, have been identified in skeletal muscle.
• These structures were observed in a mother and one of her two children, all exhibiting percussion myotonia.

Purpose of the Study:

• To investigate the nature and origin of cylindrical spirals in skeletal muscle.
• To correlate the presence of these structures with clinical symptoms of myotonia.

Main Methods:

• Electron microscopy was used to examine skeletal muscle biopsies.
• Clinical assessment of muscle function and symptoms was performed.

Main Results:

• Cylindrical spirals (8 μm long, 1 μm wide) composed of spiraling double-laminate membrane were detected.
• These structures originate from abnormal subsarcolemmal tubulovesicular formations, interpreted as pathological T-tubules.
• The disorder, characterized by percussion myotonia, muscle stiffness, and myotonic lid lag, progresses with age but shows no muscle weakness or atrophy.

Conclusions:

• Cylindrical spirals are a distinct pathological finding in skeletal muscle associated with myotonia.
• The structures appear to be derived from aberrant T-tubules.
• The clinical presentation is variable, ranging from asymptomatic in children to mildly incapacitating in adults, with symptoms worsening with age.