Andrew Norris, MD PhD
Director, Pediatric Endocrinology & Diabetes
University of Iowa Stead Family Children’s Hospital
In pediatrics and medicine we are taught various rules that help us interrogate a person’s health . However, there are a variety of endocrine disorders that alter normal physiology such that the usual rules no longer apply. Failure to recognize this can lead to erroneous interpretation of a person’s condition, sometimes with even fatal results
“Good urine output indicates that a child is well hydrated”
This is a stalwart rule in pediatrics. When a child is making plenty of urine, this proves that the child is well hydrated. In general this is sage advice, but there are important endocrine exceptions:.
- Hyperglycemia / diabetes mellitus: When a child’s blood sugar is elevated, this produces an obligate osmotic diuresis. As a result, urine output remains brisk even when the child has become significantly dehydrated. To further exacerbate this, hyperglycemia leads to an osmotic fluid shift from the interstitium to the intravascular compartment, further increasing renal fluid output at the expense of worsening whole body hydration status. For these reasons, the child presenting with severe hyperglycemia is typically more dehydrated than the history and physical examination would suggest. There are cases where clinicians have been falsely reassured by a vomiting child’s brisk urine output, concluding that everything is fine when the child truly has severe hyperglycemia, with sometimes fatal consequences. Pediatricians in training are advised to become practiced and adept at asking children and families about any changes in thirst and urination, as this can be a fairly effective screening tool to assess for out-of-control undiagnosed severe diabetes.
- Diabetes insipidus: In the child who has diabetes insipidus, urine output is not a reliable indicator of hydration status. When diabetes insipidus is not treated, brisk urine output occurs even in the face of dehydration. When diabetes insipidus is treated with vasopressin or DDAVP, urine output diminishes when the medication is active, even when hydration status is excellent.
“Children and adolescents can tolerate the physical stress of fever or vomiting.”
Typically, children can tolerate common physiological stressors such as significant febrile illness or vomiting / fasting during gastroenteritis. However, often children with underlying medical conditions do not tolerate such physiological stressors as well. Included in such underlying illnesses are several important and relatively common endocrine conditions
- Adrenal insufficiency: An important component of the response to physiologic stress is increased secretion of adrenal hormones, especially cortisol. Children who are unable to secrete adequate amounts of cortisol can experience hypoglycemia, hyponatremia, and sometimes even cardiovascular collapse in response to physiologic stressors that ordinarily a child could tolerate without difficulty. Conditions in which cortisol secretion in response to stress can be impaired include panhypopituitarism, central adrenal insufficiency, congenital adrenal hyperplasia, Addison’s disease, iatrogenic adrenal suppression, and any form of hypoadrenalism. Children who have impaired mineralocorticoid secretion are at even greater risk for electrolyte imbalance, specifically hyponatremia and hyperkalemia, and cardiovascular collapse. common causes of mineralocorticoid deficiency include congenital adrenal hyperplasia and Addison’s disease. Fortunately stress dose hydrocortisone is an effective means to treat children with these conditions and enable them to better tolerate physiologic stressors.
- Diabetes mellitus: Pediatric patients with diabetes require special attention to blood glucose and Insulin management during times of physiological stress. During such times, especially in patients with type 1 diabetes, there will be an increased risk of dysglycemia, ketones, dehydration, and diabetic ketoacidosis.
- Hyperthyroidism: Patients who have active hyperthyroidism can experience significant deterioration during physiological stress and illness. In some cases, illness can precipitate thyroid storm, which can include life-threatening hyperthermia, confusion, diarrhea, tachycardia, arrhythmia, cardiovascular collapse, and coma.
“Children and adolescents tolerate exercise well”
In general children and adolescents can exercise seemingly ad infinitum. however there are a number of medical exceptions to this, including situations in which it is not entirely safe for a child to exercise vigorously. Several endocrine conditions are included among these exceptions to this common rule.
- Hyperthyroidism: Children and adolescents with active hyperthyroidism typically experience a degree of exercise intolerance. If the hyperthyroidism is significant, some patients will even experience cardiovascular decompensation and/or hyperthermia triggered by vigorous exercise.
- Ketonemia: children with diabetes can benefit greatly from exercise. however, when diabetes and ketones are present, exercise can exacerbate the degree of ketonemia, and in extreme cases can contribute to the development of diabetic ketoacidosis. standard advice during ketonemia in pediatric patients with diabetes is to administer supplemental insulin, optimize hydration, and delay a vigorous exercise until after the ketones have been cleared.
“Children do not experience electrolyte problems as long as renal function is normal and fluid / electrolyte intake is adequate.”
Although adequate fluid and electrolyte intake coupled with normal renal function is typically sufficient to maintain normal electrolyte balance, there are important exceptions to this rule especially in the endocrine system.
- Diabetes insipidus: Patients with untreated diabetes insipidus generally develop hypernatremia during normal intakes of fluid and electrolytes. provision of greater than normal amounts of free water and or medical treatment of the diabetes insipidus is required to prevent hypernatremia.
- SIADH (syndrome of inappropriate ADH secretion): Patients with SIADH have a tendency towards hyponatremia when provided normal amounts of fluid and electrolyte. Fluid restriction is commonly used to prevent hyponatremia in such patients.
- Mineralocorticoid deficiency: Patients with untreated mineralocorticoid deficiency are prone to hyponatremia and hyperkalemia despite normal fluid and electrolyte intake. Common pediatric causes of mineralocorticoid deficiency include congenital adrenal hyperplasia and Addison’s disease.
“Failure of an infant to gain weight is a feeding issue.”
Many times, when an infant is not adequately gaining weight this can indicate various feeding issues. However, there are many medical diseases which can cause poor weight gain during infancy for reasons other than poor nutritional intake. There are several important to endocrine diseases among these conditions. Congenital adrenal hyperplasia typically causes poor weight gain and failure to thrive beginning towards the end of the first week of life. Neonatal Graves disease, when severe, presents with failure of a newborn to gain weight typically in the first week or two of life. Neonatal diabetes mellitus can present at various times in the first six months of life and can lead to poor weight gain.