Emergency management of inherited metabolic diseases

Inherited metabolic diseases with acute severe manifestations can be divided into five categories: (1) disorders of the intoxication type, (2) disorders with reduced fasting tolerance, (3) disorders with disturbed energy metabolism, (4) disorders of neurotransmission and (5) disorders in which no specific emergency treatment is available. Diagnostic emergency laboratory evaluation should cover all differential diagnoses that are therapeutically relevant and should always include ammonia, glucose, lactate and acid-base status as well as testing the urine for ketones. These are indispensable for planning and conducting the first steps of metabolic emergency treatment and should be available within 30 min. According to the clinical situation and biochemical derangement, special metabolic investigations must be initiated in parallel. These include acylcarnitine profiling with tandem mass spectrometry (in plasma or dried blood spots) and analysis of amino acids in plasma and of organic acids in urine. The results of all laboratory investigations relevant to the diagnosis of metabolic disorders for which specific emergency therapy exists should be available within 24 h. There is general agreement with regard to some therapeutic strategies that are clearly explained by pathophysiology: in disorders with endogenous intoxication, anabolism must be promoted and specific detoxification measures initiated. In disorders with reduced fasting tolerance, administration of glucose at the rate of hepatic glucose production forms the basis of treatment. Correction of acidosis is a major goal in disorders with disturbed mitochondrial energy metabolism, while glucose supply may have to be limited. Many current therapeutic strategies are based on case reports and personal experiences at different metabolic centres. The aim of devising the 'best' management is often hampered by the lack of objective evidence of efficacy.