Infantile reversible cytochrome c oxidase (COX) deficiency myopathy is a mitochondrial rare disease with onset age of first day to three months with symptoms of generalized muscle weakness and severe hypotonia. Despite its initial serious conditions, the symptoms may improve spontaneously later in their life, with the so-called "benign" myopathy accordingly. This benign mitochondrial myopathy might be improved in their later life, which is different from most mitochondrial myopathies with progression by age. Therefore, we depicted the rare case of her clinical course during our medical practice, anticipating to provide more information of this rare disease.
