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Lipid storage myopathy with normal carnitine levels
Insights
This study describes a lipid storage myopathy case with non-progressive muscle weakness. Muscle biopsies revealed abnormal fat spaces and slight mitochondrial changes, ruling out carnitine deficiency.
Area of Science:
- Neurology
- Muscle Physiology
- Biochemistry
Background:
- Lipid storage myopathies are rare neuromuscular disorders.
- They can present with muscle weakness and fatigue.
- Differential diagnosis includes various metabolic and genetic causes.
Purpose of the Study:
- To investigate the underlying mechanisms of a lipid storage myopathy in an adult patient.
- To characterize the muscle pathology and rule out specific biochemical defects.
Main Methods:
- Muscle biopsy and histopathological analysis (light and electron microscopy).
- Morphometric analysis of muscle fiber components.
- Biochemical assays for carnitine and carnitine palmityltransferase levels.
Main Results:
- Muscle biopsies showed abnormal lipid spaces in type I and type II fibers with type I fiber predominance.
- Electron microscopy revealed lipid excess and normal mitochondria on initial inspection, but morphometry indicated decreased mitochondrial size and sarcotubular membrane concentration in cross-sections.
- Serum and muscle carnitine and carnitine palmityltransferase levels were normal.
Conclusions:
- The patient presented with a lipid storage myopathy not caused by carnitine deficiency.
- Lipid storage myopathy is a syndrome with diverse etiologies, necessitating comprehensive biochemical investigation.
- Further research is needed to elucidate the specific biochemical defects in non-carnitine-deficient lipid storage myopathies.
Abstract:
A 28-year-old female, who showed a floppy baby syndrome during early infancy, had a non-progressive proximal muscle weakness with easy fatiguability since childhood. Two muscle specimens biopsied at the age of 28 years revealed myriads of 1-3-mum wide abnormal spaces containing neutral fat in type I and type II fibers. Both biopsies demonstrated a type I fiber preponderance. Electron microscopy demonstrated lipid excess and normal mitochondria by simple inspection. The mitochondrial area and sarcotubular membrane profile concentration in morphometry of longitudinal sections were also normal. Cross-sections, however, revealed a slight decrease of the individual mitochondrial size and of the sarcotubular membrane profile concentration . Serum and muscle carnitine levels and the muscle carnitine palmityltransferase level were all within normal range. Besides carnitine deficiency other biochemical defects can occur in lipid storage myopathy, which represents a syndrome rather than a unique disease entity.