MSUD is disorder affecting the breakdown of branched chain amino acids (BCAA = Leucine, Isoleucine & Valine). In classical (severe) MSUD the only significant pathway for the removal of BCAA is via protein synthesis as there is very little renal excretion. The encephalopathy is the result of accumulation of the BCAA (particularly leucine), which are toxic at high concentrations. There may be no hypoglycaemia, hyperammonaemia or acidosis. Plasma amino acids can seldom be measured urgently, so management has to be based on the clinical state. Decompensation is often triggered by metabolic stress such as febrile illness, particularly gastroenteritis or fasting but an obvious cause is not always apparent. The early signs of decompensation may be subtle, lethargy or ataxia. Vomiting is common and should always be taken seriously. However the signs may be difficult to assess such as irritability or just ‘not right’.
Sections of this guideline include: background, admission, initial and ongoing management, oral and intravenous feeding, progress monitoring and discharge.