Late onset lipid storage myopathy due to multiple acyl CoA dehydrogenase deficiency triggered by valproate.

Late onset Multiple Acyl CoA dehydrogenase (MAD) deficiency myopathy is a rare disorder. Only five cases have been reported. We report one case with MAD deficiency in which the clinical features appeared during valproic acid therapy. A 47-yr-old man taking valproic acid for 4 months presented nocturnal calf cramps, exercise intolerance, difficulty in climbing stairs and shortness of breath. Muscle biopsy revealed ragged red fibres and neutral lipid storage. Electron microscopy showed enlarged abnormal mitochondria with abnormal internal structure. The total and free muscle carnitine was decreased. The activities of all short, medium and long chain acyl CoA dehydrogenases were 40% of the normal. In this case a partial defect of MAD is noted, possibly triggered by valproic acid, causing the clinical manifestations of the pre-existing myopathy. After discontinuation of the drug a clinical improvement was observed while therapy with riboflavin resulted in a total relief of the symptoms.