Medical School · Year 3 · Pediatrics · includes a quiz and discussion video

Seminar 10: Pediatric Endocrine Disorders

Year 3: Pediatrics Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Evaluate and manage diabetes mellitus in children
2. Recognize thyroid disorders
3. Diagnose and treat growth disorders
4. Identify adrenal disorders including CAH
5. Recognize disorders of puberty
6. Describe bone and mineral metabolism disorders

Lecture Outline

I. Type 1 Diabetes Mellitus

Type 1 diabetes mellitus represents an autoimmune disease characterized by destruction of pancreatic beta cells leading to absolute insulin deficiency, accounting for the majority of diabetes cases in children and adolescents. The pathophysiology involves T-cell mediated destruction of beta cells in genetically susceptible individuals, with HLA-DR3 and HLA-DR4 conferring the greatest risk, triggered by environmental factors that remain incompletely understood. Autoantibodies including glutamic acid decarboxylase (GAD65), insulinoma-associated antigen 2 (IA-2), insulin autoantibodies, and zinc transporter 8 antibodies serve as markers of the autoimmune process and can be detected months to years before clinical presentation. Peak incidence occurs bimodally at ages 5-7 years and during puberty, with rates increasing worldwide for unclear reasons.

Clinical presentation of type 1 diabetes results from hyperglycemia and insulin deficiency, with the classic triad of polyuria, polydipsia, and weight loss despite polyphagia. Polyuria results from osmotic diuresis as glucose exceeds the renal threshold for reabsorption, leading to compensatory polydipsia to maintain hydration. Weight loss occurs because without insulin, the body cannot utilize glucose and begins breaking down fat and muscle for energy, leading to the characteristic weight loss despite increased appetite and food intake. Approximately 30-40% of children present in diabetic ketoacidosis at initial diagnosis, particularly younger children in whom symptoms may be attributed to other causes, making early recognition of diabetes symptoms critical.

Diagnosis of type 1 diabetes requires demonstration of hyperglycemia meeting established criteria. A random plasma glucose of 200 mg/dL or greater with classic symptoms (polyuria, polydipsia, weight loss) is diagnostic, requiring no confirmatory testing. Fasting plasma glucose of 126 mg/dL or greater, HbA1c of 6.5% or greater, or 2-hour plasma glucose of 200 mg/dL or greater during an oral glucose tolerance test also establish diagnosis, with confirmation on a separate day in asymptomatic patients. C-peptide levels, which reflect endogenous insulin production, are low or undetectable in type 1 diabetes and help distinguish it from type 2 diabetes in ambiguous presentations. Islet cell autoantibodies support the diagnosis of type 1 diabetes and predict beta cell destruction.

Insulin therapy is essential and lifelong, with regimens designed to mimic physiologic insulin secretion as closely as possible. Basal-bolus regimens use long-acting insulin (glargine, detemir, degludec) to provide background insulin coverage and rapid-acting insulin (lispro, aspart, glulisine) at meals to cover carbohydrate intake. Continuous subcutaneous insulin infusion (insulin pump therapy) delivers rapid-acting insulin continuously with additional boluses for meals and corrections, offering flexibility and improved glycemic control for many patients. Initial total daily insulin requirements are typically 0.5-1 unit/kg/day, adjusted based on glucose monitoring results. The honeymoon period, occurring in many patients after diagnosis, involves temporarily reduced insulin requirements as residual beta cell function recovers, but this remission is temporary and insulin requirements subsequently increase.

<image>Panel A: Type 1 diabetes pathophysiology showing autoimmune beta cell destruction, HLA associations, autoantibodies, and environmental triggers with timeline from genetic susceptibility to clinical presentation. Panel B: Classic symptoms triad of polyuria, polydipsia, and weight loss with pathophysiology of osmotic diuresis and catabolic state. Panel C: Diagnostic criteria comparison showing random glucose, fasting glucose, HbA1c, and OGTT thresholds with confirmatory testing requirements. Panel D: Insulin regimen comparison showing basal-bolus with long-acting and rapid-acting insulin versus continuous subcutaneous insulin infusion pump therapy with advantages and considerations for each.</image>

II. Diabetic Ketoacidosis

Diabetic ketoacidosis represents a life-threatening complication of diabetes characterized by the triad of hyperglycemia, metabolic acidosis, and ketosis, occurring in absolute or relative insulin deficiency states. The pathophysiology involves insufficient insulin action leading to unrestrained hepatic gluconeogenesis and glycogenolysis causing hyperglycemia, while accelerated lipolysis releases free fatty acids that are converted to ketone bodies in the liver. Ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) accumulate and cause high anion gap metabolic acidosis, while osmotic diuresis from hyperglycemia leads to dehydration and electrolyte losses. DKA may occur as the initial presentation of type 1 diabetes, as a consequence of insulin omission or inadequate dosing in known diabetics, or precipitated by illness or infection that increases insulin requirements.

Diagnosis of DKA requires laboratory confirmation of hyperglycemia, acidosis, and ketosis. Diagnostic criteria include blood glucose greater than 200 mg/dL, venous pH less than 7.3 or bicarbonate less than 15 mEq/L, and the presence of ketonemia or ketonuria. Severity is classified by degree of acidosis: mild DKA has pH 7.2-7.3 and bicarbonate 10-15, moderate DKA has pH 7.1-7.2 and bicarbonate 5-10, and severe DKA has pH less than 7.1 and bicarbonate less than 5. The anion gap is elevated, calculated as sodium minus chloride plus bicarbonate, reflecting the presence of unmeasured ketoacid anions. Additional laboratory abnormalities include elevated serum potassium (despite total body potassium depletion from urinary losses), elevated BUN from dehydration, and potentially elevated white blood cell count even without infection.

Management of DKA follows a systematic approach addressing fluid resuscitation, insulin therapy, and electrolyte replacement. Initial fluid resuscitation uses isotonic saline at 10-20 mL/kg over 1-2 hours for patients with significant dehydration, followed by calculation of total fluid deficit to be replaced over 24-48 hours along with maintenance fluids. Insulin infusion begins after initial fluid resuscitation, typically at 0.05-0.1 units/kg/hour, with the goal of gradual glucose reduction at approximately 50-100 mg/dL per hour. Potassium replacement is added early since total body potassium is depleted despite potentially normal or elevated serum levels, and serum potassium falls rapidly with insulin therapy and acidosis correction. Dextrose is added to intravenous fluids when blood glucose reaches 250-300 mg/dL to prevent hypoglycemia while continuing insulin infusion until acidosis resolves.

Cerebral edema represents the most feared complication of DKA treatment, occurring in approximately 1% of DKA episodes but accounting for the majority of DKA-related deaths and neurological morbidity. Risk factors include younger age, new-onset diabetes, longer symptom duration, greater dehydration, and more severe acidosis at presentation. Clinical features include headache, altered mental status, bradycardia, hypertension, and subsequent neurological deterioration that may progress rapidly. Prevention focuses on gradual correction of hyperglycemia and dehydration, avoiding large boluses of hypotonic fluids, and maintaining serum sodium rise as glucose falls. Treatment of suspected cerebral edema includes immediate administration of mannitol or hypertonic saline, head elevation, fluid restriction, and preparation for possible intubation and intensive care, without waiting for imaging confirmation if clinical suspicion is high.

<image>Panel A: DKA pathophysiology flowchart showing insulin deficiency leading to hyperglycemia (gluconeogenesis, glycogenolysis), ketogenesis (lipolysis, fatty acid oxidation), and osmotic diuresis with dehydration. Panel B: DKA severity classification showing mild, moderate, and severe categories based on pH and bicarbonate levels with corresponding clinical features. Panel C: DKA management protocol showing stepwise approach with initial fluid resuscitation, insulin infusion timing and rate, potassium replacement, and dextrose addition with monitoring parameters. Panel D: Cerebral edema recognition and management showing risk factors, clinical features (headache, altered mental status, Cushing triad), and immediate treatment with mannitol/hypertonic saline.</image>

III. Type 2 Diabetes Mellitus

Type 2 diabetes mellitus in children has increased dramatically parallel to the obesity epidemic and now accounts for up to one-third of new diabetes diagnoses in adolescents. The pathophysiology involves insulin resistance in peripheral tissues combined with relative beta cell dysfunction, differing fundamentally from the autoimmune destruction of type 1 diabetes. Risk factors include obesity (particularly with BMI above the 95th percentile), family history of type 2 diabetes in first- or second-degree relatives, minority race/ethnicity with highest rates in Native American, African American, Hispanic, and Asian/Pacific Islander populations, and clinical signs of insulin resistance including acanthosis nigricans and polycystic ovary syndrome.

Clinical presentation of type 2 diabetes in youth is often insidious, with many patients identified through screening rather than symptomatic presentation. When symptoms occur, they include the classic polyuria and polydipsia but are typically less severe than in type 1 diabetes, and significant weight loss is uncommon given the underlying obesity. Physical examination often reveals obesity with central adiposity, acanthosis nigricans (hyperpigmented velvety skin in body folds indicating insulin resistance), and hypertension. Notably, up to one-third of youth with type 2 diabetes may present with ketosis or even diabetic ketoacidosis, making differentiation from type 1 diabetes challenging in the acute setting.

Screening for type 2 diabetes is recommended for youth who are overweight or obese with additional risk factors. Current guidelines recommend screening beginning at age 10 or at onset of puberty (whichever comes first) in overweight children with body mass index at or above the 85th percentile who have at least one additional risk factor. Risk factors include family history of type 2 diabetes, high-risk race/ethnicity, signs of insulin resistance (acanthosis nigricans, hypertension, dyslipidemia, polycystic ovary syndrome), or maternal history of gestational diabetes. Screening is performed with fasting glucose, HbA1c, or oral glucose tolerance test, repeated every 3 years if initial results are normal.

Treatment of type 2 diabetes in youth begins with lifestyle modification addressing diet and physical activity, which remains the foundation of therapy regardless of pharmacological intervention. Dietary counseling emphasizes reduction of caloric intake, elimination of sugar-sweetened beverages, increased consumption of fruits, vegetables, and whole grains, and family involvement in dietary changes. Physical activity recommendations include at least 60 minutes of moderate-to-vigorous activity daily with reduction of sedentary screen time. Metformin is the first-line pharmacological agent, improving insulin sensitivity and reducing hepatic glucose production, with gastrointestinal side effects minimized by gradual dose titration. Insulin therapy is initiated if HbA1c is 8.5% or greater at diagnosis, if ketosis or acidosis is present, or if lifestyle and metformin fail to achieve glycemic targets.

<image>Panel A: Type 2 diabetes pathophysiology in youth showing insulin resistance in muscle, liver, and adipose tissue combined with beta cell dysfunction, contrasted with autoimmune pathophysiology of type 1. Panel B: Risk factors displayed on body diagram showing obesity with central adiposity, acanthosis nigricans on neck, and associated conditions including hypertension and PCOS. Panel C: Screening criteria flowchart showing age and BMI thresholds plus required additional risk factors with screening test options and interval. Panel D: Treatment algorithm showing lifestyle modification as foundation, metformin as first-line pharmacotherapy with dosing, and indications for insulin initiation.</image>

IV. Thyroid Disorders

Congenital hypothyroidism affects approximately 1 in 3,000 newborns and represents one of the most common preventable causes of intellectual disability, making newborn screening and early treatment essential. The most common etiology is thyroid dysgenesis, encompassing aplasia, hypoplasia, or ectopic thyroid tissue, accounting for approximately 85% of cases, with dyshormonogenesis (defects in thyroid hormone synthesis) causing most remaining cases. Newborn metabolic screening programs detect elevated TSH in affected infants, typically within the first few days of life, allowing diagnosis before clinical manifestations develop. Clinical features, when present, include prolonged physiologic jaundice, hypotonia, large fontanelles, feeding difficulties, constipation, and macroglossia, though many affected infants appear normal at birth.

Treatment of congenital hypothyroidism must begin promptly, ideally within the first two weeks of life, to optimize neurodevelopmental outcomes. Levothyroxine is the treatment of choice, initiated at 10-15 mcg/kg/day in neonates, with higher doses needed than at any other age due to the critical developmental requirement for thyroid hormone. Close monitoring with TSH and free T4 ensures adequate replacement, with the goal of normalizing TSH and maintaining free T4 in the upper half of the normal range. Prognosis with early diagnosis and treatment is excellent, with normal intellectual development expected, though there remains a slightly increased risk of subtle neurocognitive deficits compared to unaffected children.

Acquired hypothyroidism in children is most commonly caused by Hashimoto's (chronic lymphocytic) thyroiditis, an autoimmune condition characterized by anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies. Clinical features develop gradually and include fatigue, cold intolerance, constipation, weight gain, dry skin, hair loss, and goiter (which may be the presenting finding). Growth effects include decreased linear growth velocity and delayed skeletal maturation (bone age younger than chronological age), while pubertal effects vary with some patients experiencing delayed puberty and others paradoxically developing precocious puberty. Laboratory findings show elevated TSH with low free T4 in overt hypothyroidism or elevated TSH with normal free T4 in subclinical hypothyroidism, and treatment with levothyroxine is indicated for overt disease and considered for subclinical cases with significantly elevated TSH.

Hyperthyroidism in children is most commonly caused by Graves' disease, an autoimmune condition in which thyroid-stimulating immunoglobulins (TSI) activate the TSH receptor causing overproduction of thyroid hormone. Clinical features include weight loss despite increased appetite, heat intolerance, palpitations, tachycardia, tremor, emotional lability, and impaired concentration affecting school performance. Physical findings include goiter, proptosis (exophthalmos), eyelid lag, warm and moist skin, and potentially thyroid bruit. First-line treatment involves antithyroid medications, with methimazole preferred over propylthiouracil (PTU) in children due to PTU's association with severe liver injury, though PTU may be preferred in the first trimester of pregnancy or during thyroid storm. Beta-blockers provide symptomatic relief of tremor and tachycardia while awaiting antithyroid medication effect, and definitive treatment with radioactive iodine ablation or thyroidectomy is considered for refractory cases or severe disease.

<image>Panel A: Congenital hypothyroidism showing etiologies (dysgenesis, dyshormonogenesis), newborn screening protocol, clinical features when present, and critical importance of early treatment for neurodevelopment. Panel B: Hashimoto's thyroiditis showing autoimmune pathophysiology with anti-TPO and anti-Tg antibodies, clinical features including goiter and growth effects, and laboratory findings with treatment approach. Panel C: Graves' disease pathophysiology showing TSI activation of TSH receptor, clinical features with exophthalmos and thyroid examination findings, and treatment options from antithyroid medications to definitive therapy. Panel D: Thyroid function test interpretation showing TSH and free T4 patterns in primary hypothyroidism, secondary hypothyroidism, and hyperthyroidism with clinical correlates.</image>

V. Growth Disorders

Normal growth follows predictable patterns that vary by age, with deviations from these patterns serving as important indicators of underlying disease. In the first year of life, infants grow approximately 25 cm in length, with growth most rapid in the first few months and then decelerating. During the second year, children grow approximately 12 cm, and from ages 2 to puberty, the growth rate stabilizes at approximately 5-6 cm per year. The pubertal growth spurt produces accelerated growth of 8-12 cm per year, occurring earlier in girls (at approximately 12 years) than boys (at approximately 14 years), with final height determined by genetic potential, hormonal factors, and overall health.

Short stature evaluation begins with accurate measurement and plotting on appropriate growth charts, distinguishing between normal variants and pathological causes. The most common causes of short stature are familial short stature (child is short but growing at a normal rate, with short parents and predicted adult height consistent with family) and constitutional growth delay (child is short with delayed bone age but normal growth rate, typically with family history of delayed puberty, who will eventually achieve normal adult height). Pathological causes include chronic diseases affecting growth (celiac disease, inflammatory bowel disease, chronic kidney disease, congenital heart disease), endocrine disorders (growth hormone deficiency, hypothyroidism, Cushing syndrome), and genetic syndromes (Turner syndrome in girls, Down syndrome, Noonan syndrome).

Evaluation of short stature involves careful history, physical examination, and targeted laboratory and radiologic testing. Growth chart review assesses growth velocity and pattern over time, with falling across percentile lines concerning for pathology. Bone age radiograph of the left hand provides skeletal maturity assessment, which is delayed in constitutional delay and hypothyroidism, normal in familial short stature, and advanced in precocious puberty. Screening laboratories include complete blood count, comprehensive metabolic panel, thyroid function tests, and celiac serologies, with additional testing based on clinical suspicion. In girls with short stature without other explanation, karyotype should be obtained to evaluate for Turner syndrome. IGF-1 and IGFBP-3 reflect growth hormone axis function, with low levels suggesting growth hormone deficiency that may warrant provocative testing.

Growth hormone deficiency may be congenital or acquired and presents with short stature, decreased growth velocity, and delayed bone age. Congenital causes include genetic mutations affecting the GH-IGF-1 axis, midline defects, and idiopathic GH deficiency, while acquired causes include tumors (particularly craniopharyngioma), cranial irradiation, and traumatic brain injury. Diagnosis requires demonstration of inadequate GH secretion on provocative testing (typically using insulin, arginine, clonidine, or glucagon stimulation) in the context of clinical features and low IGF-1. Treatment with recombinant growth hormone, administered as daily subcutaneous injections, increases growth velocity and improves final height, though response depends on timing of initiation, dose, and underlying diagnosis.

<image>Panel A: Normal growth velocity chart by age showing rapid infant growth, stable childhood rate of 5-6 cm/year, and pubertal growth spurt with gender differences in timing. Panel B: Short stature differential diagnosis divided into normal variants (familial, constitutional delay) and pathological causes (chronic disease, endocrine, genetic) with distinguishing features of each. Panel C: Short stature evaluation algorithm showing growth chart analysis, bone age assessment, screening laboratories, and indication for karyotype and GH axis testing. Panel D: Growth hormone deficiency features, provocative testing protocol, diagnostic criteria, and treatment with recombinant GH showing expected response and monitoring parameters.</image>

VI. Adrenal Disorders

Congenital adrenal hyperplasia encompasses a group of autosomal recessive disorders caused by enzyme deficiencies in the cortisol biosynthesis pathway, with 21-hydroxylase deficiency accounting for approximately 95% of cases. The enzyme deficiency blocks cortisol synthesis, leading to decreased negative feedback on the hypothalamic-pituitary axis and increased ACTH secretion, which drives adrenal hyperplasia and accumulation of precursor steroids. In 21-hydroxylase deficiency, accumulated precursors are shunted toward androgen synthesis, causing virilization, while the classic salt-wasting form also has impaired aldosterone synthesis causing renal salt loss. Newborn screening programs detect elevated 17-hydroxyprogesterone, allowing early diagnosis before clinical crisis in many cases.

Classic CAH presents differently in males and females due to the differential effects of prenatal androgen exposure. Affected females are born with ambiguous genitalia due to in utero virilization, ranging from mild clitoromegaly to severely virilized external genitalia that may be mistaken for male, though internal reproductive structures (ovaries, uterus, fallopian tubes) are normal. Males have normal genitalia at birth and may not be diagnosed until presenting with a salt-wasting crisis at 1-2 weeks of life, manifesting as poor feeding, vomiting, dehydration, and shock with hyponatremia and hyperkalemia. Non-classic (late-onset) CAH presents later in childhood or adolescence with signs of androgen excess including premature adrenarche, accelerated growth with advanced bone age, hirsutism, and menstrual irregularities.

Treatment of CAH requires lifelong hormone replacement to correct cortisol and aldosterone deficiency while suppressing excess ACTH and androgen production. Hydrocortisone is the glucocorticoid of choice in growing children, given in divided doses to provide cortisol replacement and suppress ACTH-driven androgen excess. Fludrocortisone provides mineralocorticoid replacement in salt-wasting forms, and sodium chloride supplementation may be needed in infants. Monitoring involves clinical assessment of growth, signs of androgen excess or glucocorticoid excess, and laboratory measurement of 17-hydroxyprogesterone, androgens, and renin. Stress dosing, typically tripling the hydrocortisone dose during moderate illness and using parenteral hydrocortisone during severe illness or surgery, is essential to prevent adrenal crisis.

Adrenal insufficiency beyond CAH may be primary (adrenal gland dysfunction), secondary (pituitary ACTH deficiency), or tertiary (hypothalamic CRH deficiency from chronic exogenous glucocorticoid use). Primary adrenal insufficiency causes include autoimmune adrenalitis (most common cause in developed countries after the neonatal period), infections, hemorrhage, and adrenoleukodystrophy. Tertiary adrenal insufficiency from chronic corticosteroid therapy causing hypothalamic-pituitary-adrenal axis suppression is increasingly recognized and important to prevent by using appropriate weaning protocols. Acute adrenal crisis presents with hypoglycemia, hypotension, shock, hyponatremia, and hyperkalemia, requiring emergent fluid resuscitation and hydrocortisone administration. Patients with known adrenal insufficiency require medic alert identification and emergency hydrocortisone for stress situations.

<image>Panel A: 21-hydroxylase deficiency pathway showing enzyme block, decreased cortisol and aldosterone, increased ACTH drive, and shunting to androgen pathway with elevated 17-OHP. Panel B: Classic CAH presentation comparing females (ambiguous genitalia, Prader staging) with males (normal at birth, salt-wasting crisis presentation with electrolyte abnormalities). Panel C: CAH treatment protocol showing hydrocortisone replacement dosing, fludrocortisone for salt-wasting, monitoring parameters, and stress dosing guidelines. Panel D: Adrenal insufficiency types showing primary (autoimmune, infection), secondary (pituitary), and tertiary (steroid suppression) with distinguishing laboratory patterns and adrenal crisis management.</image>

VII. Pubertal Disorders

Precocious puberty is defined as the development of secondary sexual characteristics before age 8 in girls and age 9 in boys, requiring evaluation to determine the underlying cause and appropriate management. Central precocious puberty results from premature activation of the hypothalamic-pituitary-gonadal axis and represents "true" puberty with the normal pubertal process occurring earlier than expected. Causes of central precocious puberty include idiopathic (most common in girls), central nervous system lesions (hypothalamic hamartoma, tumors, hydrocephalus), and prior CNS injury or irradiation, with boys being more likely to have an identifiable organic cause. Peripheral precocious puberty is GnRH-independent, caused by sex steroid exposure from gonadal or adrenal tumors, McCune-Albright syndrome, congenital adrenal hyperplasia, or exogenous hormone exposure.

Evaluation of precocious puberty involves careful assessment of pubertal staging, growth, and targeted laboratory and imaging studies. Tanner staging documents breast and pubic hair development in girls and genital and pubic hair development in boys, with progression over time providing important information about rapidity of pubertal advance. Bone age is typically advanced in true precocious puberty due to the effect of sex steroids on skeletal maturation. Laboratory evaluation includes LH, FSH, estradiol (girls) or testosterone (boys), with pubertal LH levels and an LH-predominant LH:FSH ratio suggesting central precocious puberty. GnRH (or GnRH agonist) stimulation testing confirms central activation by demonstrating pubertal LH response. MRI of the brain with attention to the hypothalamic-pituitary region is indicated in all boys with central precocious puberty and in girls with early onset, rapid progression, or neurological symptoms.

Treatment of central precocious puberty with GnRH agonists effectively halts and may reverse pubertal progression by desensitizing pituitary gonadotropes after initial stimulation. Indications for treatment include rapidly progressive puberty, significant bone age advancement predicting compromised adult height, and psychological distress related to early puberty. GnRH agonists (leuprolide, histrelin) are administered as monthly or 3-monthly injections or as implants, with monitoring of growth, pubertal progression, and suppressed gonadotropins confirming therapeutic effect. Treatment is typically continued until an appropriate age for puberty (usually 11-12 years in girls), at which point therapy is discontinued and puberty resumes.

Delayed puberty is defined as absence of breast development by age 13 in girls or testicular enlargement by age 14 in boys, requiring evaluation when present. Constitutional delay of growth and puberty is the most common cause, representing the opposite end of normal variation, with affected individuals having delayed but ultimately normal puberty and family history often revealing similar patterns. Hypogonadotropic hypogonadism involves low FSH and LH due to hypothalamic or pituitary dysfunction, caused by Kallmann syndrome (with anosmia), other genetic conditions, tumors, or functional causes including eating disorders, excessive exercise, and chronic illness. Hypergonadotropic hypogonadism involves elevated FSH and LH due to gonadal failure, with Turner syndrome (45,X) in girls and Klinefelter syndrome (47,XXY) in boys being common causes. Treatment depends on underlying etiology and typically involves hormone replacement therapy.

<image>Panel A: Precocious puberty classification showing central (GnRH-dependent) versus peripheral (GnRH-independent) pathophysiology with causes and distinguishing laboratory features for each. Panel B: Precocious puberty evaluation algorithm showing Tanner staging, bone age assessment, laboratory testing with GnRH stimulation, and MRI indications. Panel C: GnRH agonist treatment mechanism showing initial stimulation then desensitization, indications for treatment, monitoring parameters, and duration of therapy. Panel D: Delayed puberty differential diagnosis showing constitutional delay, hypogonadotropic hypogonadism (Kallmann, functional), and hypergonadotropic hypogonadism (Turner, Klinefelter) with evaluation and treatment approach.</image>

VIII. Bone and Mineral Disorders

Rickets represents defective mineralization of growing bone, most commonly caused by vitamin D deficiency but also resulting from calcium deficiency, phosphorus deficiency, or inherited disorders of vitamin D or phosphate metabolism. Vitamin D deficiency rickets remains common, particularly in breastfed infants without vitamin D supplementation, children with dark skin pigmentation, those with limited sun exposure, and individuals with malabsorption. The pathophysiology involves inadequate calcium absorption due to insufficient active vitamin D, leading to hypocalcemia that triggers secondary hyperparathyroidism, which maintains serum calcium at the expense of bone mineralization. Clinical features include frontal bossing, craniotabes (soft skull bones), rachitic rosary (enlarged costochondral junctions), widened wrists and ankles, and bowing of weight-bearing limbs.

Laboratory and radiographic findings in rickets reflect the underlying mineral disturbance and secondary hyperparathyroidism. Serum calcium is low or low-normal, phosphorus is low (in vitamin D deficiency) or may be the primary abnormality (in hypophosphatemic rickets), and alkaline phosphatase is markedly elevated reflecting increased osteoblast activity. 25-hydroxyvitamin D level is low in vitamin D deficiency rickets, and parathyroid hormone is elevated as a compensatory response. Radiographs of the wrists and knees show characteristic findings including metaphyseal fraying and cupping, widened physes, and osteopenia. Treatment of nutritional rickets involves vitamin D supplementation at higher doses than prophylactic amounts (typically 2,000-5,000 IU daily or higher doses weekly) along with calcium supplementation, with radiographic healing expected within 2-3 months.

Calcium homeostasis disorders include both hypocalcemia and hypercalcemia, with causes and manifestations differing from those in adults. Hypocalcemia causes neuromuscular irritability manifesting as tetany, muscle cramps, paresthesias, Chvostek sign (facial twitching with tapping over facial nerve), Trousseau sign (carpal spasm with blood pressure cuff inflation), and in severe cases seizures and laryngospasm. Causes include hypoparathyroidism (often autoimmune or post-surgical), vitamin D deficiency, pseudohypoparathyroidism (PTH resistance), and neonatal hypocalcemia. Hypercalcemia causes constipation, polyuria, abdominal pain, weakness, and altered mental status, with causes including hyperparathyroidism, malignancy, immobilization, granulomatous diseases, and Williams syndrome.

Vitamin D supplementation is recommended for all breastfed infants and many children to ensure adequate status for bone health. Current recommendations include 400 IU daily for all infants from birth regardless of feeding type, as formula-fed infants may not receive adequate amounts until consuming large volumes. Children and adolescents require 600 IU daily, which may be obtained through diet (fortified milk, fatty fish) or supplementation. Populations at higher risk for deficiency, including those with dark skin, limited sun exposure, obesity, or malabsorption, may require higher supplementation. Monitoring of vitamin D status with 25-hydroxyvitamin D levels is indicated in high-risk populations and those with clinical suspicion of deficiency, with levels above 30 ng/mL considered sufficient.

<image>Panel A: Rickets pathophysiology showing vitamin D deficiency leading to decreased calcium absorption, secondary hyperparathyroidism, and impaired bone mineralization with clinical features including bowed legs and rachitic rosary. Panel B: Laboratory findings in rickets showing low calcium, low phosphorus, elevated alkaline phosphatase, low 25-OH vitamin D, and elevated PTH with radiographic findings of metaphyseal fraying and cupping. Panel C: Calcium disorder manifestations comparing hypocalcemia (tetany, Chvostek, Trousseau, seizures) with hypercalcemia (constipation, polyuria, weakness) and causes of each. Panel D: Vitamin D supplementation recommendations by age showing 400 IU for infants, 600 IU for children/adolescents, higher-risk populations, and monitoring indications.</image>

IX. Hypoglycemia

Hypoglycemia in children represents a medical emergency requiring prompt recognition and treatment, with the definition varying somewhat by age and clinical context. Neonatal hypoglycemia is generally defined as blood glucose below 45-50 mg/dL, while in infants and children, glucose below 60-70 mg/dL is considered abnormal. Symptoms of hypoglycemia fall into two categories: adrenergic (sympathetic) symptoms including tremor, sweating, pallor, tachycardia, and hunger, and neuroglycopenic symptoms including irritability, lethargy, confusion, seizures, and coma. The clinical threshold for symptoms varies among individuals, with patients experiencing recurrent hypoglycemia potentially developing hypoglycemia unawareness with attenuated adrenergic responses.

Causes of hypoglycemia vary by age, making age-based categorization clinically useful. Neonatal hypoglycemia occurs in infants of diabetic mothers (due to fetal hyperinsulinemia), small-for-gestational-age infants (limited glycogen stores), premature infants, and infants with perinatal stress. In infants and toddlers, ketotic hypoglycemia is the most common cause, while congenital hyperinsulinism, fatty acid oxidation defects, and glycogen storage diseases require consideration. In older children, accidental ingestion of oral hypoglycemic agents or insulin, adrenal insufficiency, and reactive hypoglycemia may occur. The presence or absence of ketones during hypoglycemia provides important diagnostic information, with absent ketones suggesting hyperinsulinism or fatty acid oxidation defects where ketogenesis is suppressed.

Ketotic hypoglycemia is the most common cause of hypoglycemia in children aged 18 months to 5 years, representing a benign condition of exaggerated normal fasting intolerance. Affected children have limited glycogen stores and gluconeogenic capacity, becoming hypoglycemic during prolonged fasting or intercurrent illness when nutritional intake is reduced. Presentation typically occurs in the morning after an overnight fast or during gastrointestinal illness with poor oral intake. Laboratory findings during hypoglycemia show appropriately suppressed insulin with positive ketones (distinguishing from hyperinsulinism). Management involves avoidance of prolonged fasting, frequent snacks, and bedtime carbohydrate-rich snacks, with more aggressive intervention including intravenous dextrose during illness. The condition typically resolves by age 8-9 years as the child grows and develops larger glycogen reserves.

Congenital hyperinsulinism represents the most common cause of persistent hypoglycemia in neonates and infants, caused by genetic defects leading to inappropriate insulin secretion despite low blood glucose. Multiple genetic causes exist, with mutations in KATP channel genes (ABCC8, KCNJ11) being most common and causing either focal or diffuse disease. Clinical features include severe, recurrent hypoglycemia often requiring high glucose infusion rates to maintain euglycemia, with absent ketones and inappropriately detectable or elevated insulin during hypoglycemia. Initial management involves frequent feeds and continuous dextrose infusion, followed by medical therapy with diazoxide (which opens KATP channels to suppress insulin release) or octreotide. Surgical pancreatectomy may be required for medically unresponsive cases, with focal disease being curable by limited resection if localized with 18F-DOPA PET scanning.

<image>Panel A: Hypoglycemia symptoms divided into adrenergic (tremor, sweating, pallor, tachycardia) and neuroglycopenic (confusion, seizures, coma) categories with glucose thresholds and clinical significance. Panel B: Age-based differential diagnosis showing neonatal causes (IDM, SGA, prematurity), infant/toddler causes (ketotic hypoglycemia, hyperinsulinism, metabolic), and older child causes with ketone status as diagnostic clue. Panel C: Ketotic hypoglycemia features showing typical age range, fasting intolerance mechanism, laboratory findings with positive ketones, management with fasting avoidance, and natural resolution by age 8-9. Panel D: Congenital hyperinsulinism showing genetic causes, clinical features of severe hypoglycemia with absent ketones, medical management with diazoxide/octreotide, and surgical options for focal versus diffuse disease.</image>

X. Disorders of Sexual Development

Disorders of sex development encompass conditions with atypical development of chromosomal, gonadal, or anatomic sex, requiring multidisciplinary evaluation and management. The classification system divides DSD into sex chromosome DSD (including 45,X Turner syndrome, 47,XXY Klinefelter syndrome, and sex chromosome mosaicism), 46,XY DSD (including disorders of testicular development, disorders of androgen synthesis or action, and other causes), and 46,XX DSD (including disorders of ovarian development and androgen excess, most commonly CAH). The clinical presentation of DSD ranges from ambiguous genitalia at birth requiring urgent evaluation to milder phenotypes discovered incidentally or during evaluation for infertility.

Ambiguous genitalia at birth constitutes a medical and social urgency, requiring prompt yet thoughtful evaluation. The clinical assessment includes examination of the genital anatomy (phallic size, position of urethral meatus, presence of palpable gonads, labioscrotal appearance), assessment for signs of salt-wasting CAH (which is a medical emergency), and evaluation for other congenital anomalies suggesting syndromic conditions. Initial laboratory evaluation includes karyotype, 17-hydroxyprogesterone (to evaluate for CAH), electrolytes (for salt-wasting), and additional hormone studies including testosterone, DHT, androstenedione, and gonadotropins. Imaging with pelvic ultrasound evaluates for the presence of a uterus and helps assess gonadal structure. Gender assignment should involve the multidisciplinary team and family, considering diagnosis, genital anatomy, surgical options, hormone function, fertility potential, and family values.

Congenital adrenal hyperplasia is the most common cause of ambiguous genitalia, accounting for the majority of 46,XX DSD cases. As discussed previously, 21-hydroxylase deficiency leads to impaired cortisol and aldosterone synthesis with shunting of precursors toward androgen production, causing virilization of female fetuses with resulting ambiguous genitalia at birth. Urgent evaluation for salt-wasting, which typically presents in the first few weeks of life, is essential in any infant with ambiguous genitalia. Treatment involves hormone replacement with hydrocortisone and fludrocortisone as well as consideration of genital surgery, with timing and extent of surgery being areas of ongoing discussion.

46,XY DSD includes conditions in which individuals with male chromosomes have incomplete masculinization. Androgen insensitivity syndrome results from mutations in the androgen receptor, with complete androgen insensitivity presenting as a phenotypically female infant with inguinal or abdominal testes discovered at puberty when primary amenorrhea is evaluated. 5-alpha reductase deficiency impairs conversion of testosterone to the more potent dihydrotestosterone, causing undervirilization of external genitalia at birth with potential virilization at puberty. Disorders of testicular development include complete and partial gonadal dysgenesis. Management of these conditions requires individualized approach to gender assignment, hormone therapy, gonadal management (including cancer surveillance and timing of gonadectomy when indicated), and psychological support for patients and families.

<image>Panel A: DSD classification showing sex chromosome DSD (Turner, Klinefelter), 46,XY DSD (testicular development, androgen synthesis/action), and 46,XX DSD (ovarian development, androgen excess) with common conditions in each category. Panel B: Ambiguous genitalia evaluation algorithm showing urgent assessment, initial laboratory panel (karyotype, 17-OHP, electrolytes, hormones), imaging, and multidisciplinary team involvement. Panel C: CAH as DSD cause showing mechanism of 46,XX virilization, spectrum of genital findings, urgent evaluation for salt-wasting, and treatment considerations. Panel D: Androgen insensitivity syndrome showing complete and partial forms, clinical presentation, management including gonadal cancer surveillance, and psychosocial support framework.</image>

Summary

• Type 1 diabetes: autoimmune beta cell destruction; presents with polyuria, polydipsia, weight loss; 30-40% present in DKA
• DKA management: fluids first, then insulin infusion; replace potassium early; monitor for cerebral edema
• Type 2 diabetes: increasing in youth with obesity; screen overweight children with risk factors starting at age 10
• Congenital hypothyroidism: detected by newborn screen; treat immediately with levothyroxine for normal development
• Graves' disease: most common cause of hyperthyroidism; TSI antibodies; methimazole first-line treatment
• Short stature: familial and constitutional delay are most common; evaluate with bone age and screening labs
• CAH: 21-hydroxylase deficiency; ambiguous genitalia in females; salt-wasting crisis in males; hydrocortisone + fludrocortisone
• Precocious puberty: girls less than 8, boys less than 9; central vs peripheral; treat central with GnRH agonists
• Rickets: vitamin D deficiency causes elevated ALP, PTH; supplement all breastfed infants with 400 IU vitamin D daily
• Ketotic hypoglycemia: most common cause in toddlers; fasting intolerance; positive ketones; prevent with frequent feeds

Key Terms

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