Muscle pain, fatigue and night hypothermia in association with mitochondrial dysfunction

In case of non-specific and relatively mild muscle symptoms, the diagnosis of an inborn error of metabolism could be easily missed. Muscle pain can be the first sign of a mitochondrial disorder, especially in combination with motor developmental delay or associated organ dysfunction. Here we report on six children with a distinctive pattern of symptoms in association with variable, suboptimal mitochondrial dysfunction. This pattern exists of early onset exercise intolerance, fatigue, feeding difficulties and concentration problems associated with recurrent episodes of nocturnal hypothermia, muscle pain and mild motor retardation. No endocrine, cardiac, immunologic, neurodegenerative or psychiatric causes were found to explain these complaints. Based on the presence of muscle pain, multisystem involvement and mild lactic acidemia a mitochondrial disorder was suspected. We found decreased oxidation capacity in muscle, confirming a suboptimal mitochondrial function in our patients. Four out of five patients benefited from high dose riboflavin therapy. We think pediatricians should be aware of the possibility of a mitochondrial dysfunction in children presenting with a combination of diverse but relatively mild, "aspecific" symptoms. We advise to use the Mitochondrial Disease Criteria to evaluate the possibility of mitochondrial disease in these children.