Lipid storage myopathy associated with recurrent Reye syndrome-like attacks, but with a normal carnitine level

A case of Fukuyama-type congenital muscular dystrophy with acute carnitine deficiency triggered by fever, vomiting, and gastrointestinal bleeding

BACKGROUND

Carnitine is essential for transporting long-chain fatty acids into mitochondria and promotes energy metabolism via β-oxidation of long-chain fatty acids. Although carnitine is also present in the peripheral blood, 98% of total carnitine is stored in muscle tissue. Neuromuscular diseases accompanied by muscle atrophy are likely to lead to secondary carnitine deficiency, owing to the reduced amount of total carnitine stored in the body.

CASE PRESENTATION

An 8-y-old Japanese boy with Fukuyama-type congenital muscular dystrophy accompanied by severe psychomotor retardation had been constantly bedridden, suffered from dysphagia, and had been fed through a gastrostomy tube since the age of 1 y. Regular oral carnitine supplementation (5 mg/kg/d of levocarnitine) was initiated at the age of 7 y, which increased serum carnitine value to within the normal range (serum total carnitine concentration, 58.5-60.9 μmol/L; acylcarnitine concentration, 45.8-55.0 μmol/L; free carnitine concentration, 5.9-12.7 μmol/L). He developed a fever, vomiting, and gastrointestinal bleeding at the age of 8 y. He fell into a coma and visited an emergency room 12 h later. Hypoglycemia and hypocarnitinemia (serum total carnitine concentration, 3.7 μmol/L; acylcarnitine concentration, 2.9 μmol/L; free carnitine concentration, 0.8 μmol/L; acyl-to-free carnitine ratio, 3.6) were observed, and he was found to be negative for urinary ketone bodies.

CONCLUSIONS

Neuromuscular diseases accompanied by muscle atrophy may lead to acute carnitine deficiency, even if the serum carnitine concentration is within the normal range before onset. During sick days, it may be necessary to modify a patient's treatment, such as increasing both oral supplementation and intravenous administration of carnitine.

Update Review about Metabolic Myopathies

The aim of this review is to summarize and discuss recent findings and new insights in the etiology and phenotype of metabolic myopathies. The review relies on a systematic literature review of recent publications. Metabolic myopathies are a heterogeneous group of disorders characterized by mostly inherited defects of enzymatic pathways involved in muscle cell metabolism. Metabolic myopathies present with either permanent (fixed) or episodic abnormalities, such as weakness, wasting, exercise-intolerance, myalgia, or an increase of muscle breakdown products (creatine-kinase, myoglobin) during exercise. Though limb and respiratory muscles are most frequently affected, facial, extra-ocular, and axial muscles may be occasionally also involved. Age at onset and prognosis vary considerably. There are multiple disease mechanisms and the pathophysiology is complex. Genes most recently related to metabolic myopathy include PGM1, GYG1, RBCK1, VMA21, MTO1, KARS, and ISCA2. The number of metabolic myopathies is steadily increasing. There is limited evidence from the literature that could guide diagnosis and treatment of metabolic myopathies. Treatment is limited to mainly non-invasive or invasive symptomatic measures. In conclusion, the field of metabolic myopathies is evolving with the more widespread availability and application of next generation sequencing technologies worldwide. This will broaden the knowledge about pathophysiology and putative therapeutic strategies for this group of neuromuscular disorders.