Pediatric emergency medicine trisk 2422 2422
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risk factors are nearly as likely to have metabolic disease as sepsis. Some IEM predispose infants to
sepsis. Escherichia coli sepsis in galactosemia is the classic example. Other IEMs with increased risk of
sepsis are the organic acidemias and glycogen storage disorders.
One of the most important clues to an IEM in the neonate is a history of deterioration after an initial
period of apparent good health. The most common time that symptoms are manifest is between 2 and 5
days, but can range from hours to weeks. For neonates with IEMs of protein metabolism and
carbohydrate intolerance disorders, the onset of symptoms occurs after there has been significant
accumulation of toxic metabolites following the initiation of feeding. Initial symptoms often are poor
feeding, vomiting, irritability, and lethargy. In the neonatal period, jaundice occurs most commonly with
tyrosinemia, galactosemia, and hereditary fructose intolerance. Progression to coma, multisystem organ
failure, and death is usually rapid. Neonates with tyrosinemia may present with intracranial or pulmonary
hemorrhage due to coagulopathy. Patients with organic acidemias may have recurrent or chronic subdural
hemorrhages, sometimes mistakenly attributed to child abuse. Fatty acid oxidation disorders, particularly
very long-chain acyl-CoA dehydrogenase deficiency, may present during the neonatal period. Many of
the peroxisomal disorders and some of the mitochondrial and lysosomal disorders also present in the
neonatal period; these infants are less likely to have coma as an early manifestation and are more likely to
have dysmorphic features, brain abnormalities, skeletal malformations, cardiopulmonary compromise,
organomegaly, hepatic dysfunction, myopathy, and/or severe generalized hypotonia, usually evident at
birth. Intractable seizures due to pyridoxine- or folic acid–responsive disorders usually begin within the
first few days of life.
Infant and young child (1 month to 5 years). Infants and young children with potentially acute lifethreatening IEMs (most commonly partial deficiency of the urea cycle enzyme ornithine
transcarbamylase, fatty acid oxidation defects, disorders of carbohydrate intolerance, and disorders of
gluconeogenesis and glycogenolysis) typically present during infancy with recurrent episodes of
vomiting and lethargy, ataxia, seizures, or coma. Amino and organic acidopathies also present during
infancy, usually with progressive neurologic deterioration. Lysosomal storage disorders, mitochondrial
disorders, and peroxisomal disorders also become apparent in infancy and early childhood, usually
presenting with dysmorphism or coarse features, organomegaly, myopathy, and/or neurodegeneration.
More subtle and/or progressive findings in infants and children with IEMs include failure to thrive,
chronic dermatoses, dilated or hypertrophic cardiomyopathy, liver dysfunction, hepatomegaly,
pancreatitis, musculoskeletal weakness, hypotonia and/or cramping, impairments of hearing and vision,
and developmental delay, sometimes with loss of milestones. With routine illnesses, children with IEMs
may be more symptomatic, develop symptoms more quickly, or take longer than unaffected children to
recover. Children with disorders of protein metabolism may present with dietary changes. Fructose
intolerance often manifests between 4 and 8 months of age when fruits are introduced. Disorders with
decreased tolerance for fasting, particularly fatty acid oxidation defects and defects of gluconeogenesis
and glycogenolysis, often manifest when children have poor intake due to illness or surgery and when
infants begin to have longer overnight fasts, commonly between 7 and 12 months of age. The length of
fasting that produces symptoms may be less than 3 hours for disorders of gluconeogenesis and
glycogenolysis, and 12 to 24 hours for fatty acid oxidation defects. When patients with these disorders
present with vomiting, the severity of illness, particularly lethargy, is usually out of proportion to the
duration of illness and the amount of vomiting. IEMs also explain sudden infant death syndrome (SIDS)
in approximately 5% to 10% of cases, most commonly fatty acid oxidation defects that cause cardiac
arrest due to arrhythmia and/or cardiomyopathy; the most common of these is medium-chain fatty acylCoA dehydrogenase deficiency. Other fatty acid oxidation defects, organic acidemias, and congenital
adrenal hyperplasia account for most of the remainder of SIDS cases attributable to genetic defects.
Child >5 years of age, adolescent, or adult. In the older child, adolescent, or adult, undiagnosed
metabolic disease should be considered in individuals with subtle neurologic or psychiatric abnormalities
which may present with a history waxing/waning symptoms that have been attributed to other causes.
