Early recognition of metabolic decompensation

Many inherited metabolic diseases are complicated by episodes of decompensation and encephalopathy. These may be precipitated by catabolism, such as that associated with infections but in some cases, no acute precipitant is apparent. The clinical signs vary from one child to another but generally include abnormal behaviour, drowsiness, and a glazed look. Prompt intervention is essential if long term neurological sequelae are to be avoided. In a previous article, we have outlined our strategy for the initial management of such episodes.1 Here we consider the relative value of clinical signs and biochemical tests for the detection of decompensation. In fatty acid oxidation defects, fasting can precipitate severe encephalopathy. The mechanism of this is not fully understood: high circulating non-esterified fatty acids, low glucose, and relatively low ketone concentrations all appear to contribute. Measurement of blood glucose concentrations is sometimes recommended during intercurrent illnesses as a guide to management. In our experience, unfortunately, it is of limited value and can even be dangerous. There are two reasons for this. Firstly, blood glucose monitoring at home can only be done with reagent sticks and reflectance meters. The sensitivity of these is poor in the lower part of their range, even when performed regularly by experienced staff. Occasional measurements by parents cannot …